Animal The Definitive Visual Guide

CATFISHES AND RELATIVES 499

Gasteropelecus sternicla Hoplias macrophthalmus Electrophorus electricus one of the largest freshwater fishes in
South America. It has a continuous fin
River hatchetfish Giant trahira Electric eel that runs along its underside, but no
fins on its back; its tail tapers to a
Length 21⁄2 in Length Up to 31⁄4 ft Length Up to 81⁄4 ft sharp, finless point. Electric eels
(6.5 cm) (1 m) (2.5 m) have poor eyesight, and find their way
Weight Not recorded Weight Up to 41⁄2 lb Weight Up to 44 lb by using weak pulses of electricity.
Sex Male/Female (2 kg) (20 kg) However, using modified muscles, or
Status Not evaluated Sex Male/Female Sex Male/Female electric organs, that run the entire
Status Not evaluated Status Least concern length of their bodies, they can also
Location N. to C. South Location Trinidad, Central Location N. South produce sudden jolts of up to 600
America America to C. South America volts—powerful enough to
America kill other fishes and
potentially lethal
upturned mouth The giant trahira has a thick, stocky body Despite its name, this fish is not a true to humans.
with a blunt snout, very large eyes, and a eel, but a giant member of the knifefish
tiny somewhat rounded stomach. It has 2 or order with an eellike body. When fully tapering,
pelvic fins grown, it can be as thick as a finless tail
3 canines in its upper jaw, in addition human thigh, and is
The river hatchetfish gets its name from to a series of conical teeth. This fish continuous fin
its narrow shape, and deep, bladelike can tolerate low oxygen conditions the Dnieper River in southern Russia, on underside
keel. The most unusual feature of this and has been known to move across was over 15 ft (4.5 m) long, and weighed
silver-gray fish is its highly enlarged land at night between bodies of over 660 lb (300 kg). However, it is
pectoral fins. When threatened, or water. An important food fish, it is unlikely that any wels catfish of a similar
when chasing prey, the river hatchetfish raised in aquaculture. size exist today because they have been
uses these fins to gain speed in the heavily fished in most parts of their
water and even to take off into the air. Silurus glanis range. The wels catfish is a solitary fish, FOOD SENSORS
Marine hatchetfishes belong to a lurking at the bottom of rivers and large
different group of fishes, and have Wels catfish lakes. It moves around mainly at night,
a different lifestyle. camouflaged by its greenish gray
Location C. Europe to Length Up to 16 ft markings that conceal it against riverbed FISHES
Gymnotus carapo C. Asia (5 m) mud. Like most catfishes, it is a
Weight Up to 660 lb voracious predator, eating waterfowl and
Banded knifefish (300 kg) aquatic mammals, besides crustaceans
Sex Male/Female and smaller fishes. Females lay their
Status Least concern eggs when the water temperature rises
above 68° F (20° C). The male initially
This huge, bottom-dwelling catfish is guards both the eggs and the young. The wels catfish has 2 very long
one of the largest freshwater fishes in barbels attached to its upper jaw,
the world. The biggest specimen on and 4 smaller ones below its mouth,
record, caught in the 19th century in which help it find food.

Length 231⁄2 in large, flat HIDDEN GIANT
(60 cm) head Renowned for its extraordinary size, this well-
Weight Not recorded camouflaged fish has a large, flat head and a
Sex Male/Female
Status Not evaluated long fin that extends over half the length
of its underside.

Location Central America
to C. South America

A close relative of the electric eel long anal fin
(see above right), this freshwater fish
has a similar cylindrical body tapering Kryptopterus bicirrhis the eyes, and the region behind the region behind its head and merges with
toward its finless, rod-shaped tail. The head that contains its digestive and the base of its tail. This fish inhabits
banded knifefish is a bottom-dwelling Glass catfish reproductive organs. Its transparency lowland flood plains and large rivers
species that inhabits murky, still water. is the result of thin skin, and of body with turbid waters. Individuals gather
It produces weak electric currents Length 6 in tissues that are suffused by oils, which in small groups at an oblique angle to
with which it senses its environment. (15 cm) make its flesh translucent. The glass the water surface. Several other groups
Produced by specially adapted muscle Weight Not recorded catfish’s body is flattened from side of fishes contain species that have
tissue close to the tail, the electric Sex Male/Female to side, and its dorsal fin is reduced to transparent or nearly transparent bodies.
currents are also used to communicate Status Least concern one or 2 rays, or is missing altogether. For example, the Indian glassfish, which
with one another and for males to As in many other catfishes, it has a very actually comes from Southeast Asia, is
attract mates. It moves by rippling the Location S.E. Asia long anal fin, which stretches from the often kept in aquariums.
long fin on its underside, but it is not
a strong swimmer. deeply forked tail transparent body

dark and pale Many catfishes are camouflaged extremely long anal fin
stripes by their dark markings,
but this slender species is
long
anal fin protected by being almost
transparent. The only clearly visible
parts of its body are the backbone,

500 BONY FISHES

Ancistrus dolichopterus Farlowella acus Clarias batrachus This long-bodied catfish has the ability
to crawl overland, using its pectoral
Bushymouth catfish Whiptail catfish Philippine catfish fins to gain purchase. While on land, it
breathes through its specially modified
Length Up to 5 in Length Up to 6 in Length Up to 16 in gills, which have strengthened filaments,
(13 cm) (15 cm) (40 cm) preventing them from collapsing when
Weight Not recorded Weight Not recorded Weight Not recorded exposed to air. The Philippine catfish
Sex Male/Female Sex Male/Female Sex Male/Female lives in slow-moving water, walking
Status Least concern Status Not evaluated Status Least concern overland to reach suitable habitats. It
is a popular aquarium species; the
Location N. South America Location N.W. South Location S. and S.E. Asia piebald variety shown here is one of
America several kinds that have been bred.

The bushymouth catfish and its close long snout long dorsal barbels
relatives get their name from the fin
distinctive fleshy tentacles on the bony scutes A tiny catfish with a slender, almost
upperside of their snouts. The males cover body Vandellia cirrhosa transparent body, the candiru has an
have more tentacles than the females, unusual way of life. Instead of feeding in
giving rise to an as yet unproven theory Although they are almost all Candiru open water, it swims into the gill cavities
that they are linked to their fitness bottom dwellers, catfishes exhibit a of larger fishes—particularly larger
to breed. When threatened, the remarkable diversity of body form. Length Up to 1 in catfishes and characins—using the large,
bushymouth catfish erects its pectoral The whiptail catfish is unusually long (2.5 cm) hooked spines of its own gill cover to
and slender, with a pointed snout, and Weight Not recorded lodge itself in the gill tissue of its host. It
and dorsal fin spines, as well as the is camouflaged to resemble a piece of Sex Male/Female then bites off pieces of gill with its fine,
spines on the sides of its head. sunken wood. It lives in slow-flowing Status Not evaluated comblike teeth, and feeds on the released
rivers, and feeds mainly on river-bed blood. Candirus are notorious for
branched algae after dark. During the day, it relies Location N. South swimming up the urethras of mammals,
tentacles on its cryptic color and shape to America even humans, urinating in rivers. It is
protect it from attack. Females lay thought that, in these instances, the
FISHES armored their eggs on the river bed, and the thin, tapering body candiru mistakes the flow of urine for the
plates males guard them until they hatch.
on body stream of water expelled from the
gills of larger fishes.

Synodontis contractus Bagre marinus salinity levels. Its head has a hard, bony pectoral spines when threatened.
shield, but its most conspicuous features This fish is a bottom-feeder, eating
Upside-down catfish Gafftopsail sea catfish are the very long, flattened barbels crustaceans and other fishes. During
attached to the sides of its mouth, and the breeding season (between May and
Length 33⁄4 in Length Up to 31⁄4 ft the long spines that arch outward from its August), the male gafftopsail sea catfish
(9.5 cm) (1 m) dorsal and pectoral fins. These serrated fertilizes the female’s eggs and broods
Weight Not recorded Weight Up to 83⁄4 lb spines are also venomous and can inflict them in his mouth until they hatch.
Sex Male/Female (4 kg) painful wounds. The gafftopsail sea
Status Least concern Sex Male/Female catfish erects its dorsal and
Status Least concern
Location C. Africa Location W. Central venomous,
Atlantic, Gulf of Mexico, serrated spines
Caribbean spine has long, deeply
fleshy tendril forked tail

This African catfish swims upside-down Commercially exploited as a food
near the surface of rivers and streams, source, this Atlantic catfish is mainly
particularly when taking food from the marine, but sometimes swims into
surface or feeding from the undersides estuaries that have relatively high
of broad leaves and rocks. Its diet
includes plant material, aquatic Ameiurus nebulosus It has a scaleless body, venom glands are a formidable weapon
invertebrates, and insect larvae. The and a large mouth surrounded by against predators. Both parents guard
upside-down catfish is entirely brown or Brown bullhead 4 pairs of fleshy barbels, which it the eggs in the nest, fanning to increase
brown-violet, with a series of small spots uses to find food. Its jagged, dagger- the air flow around them, and herd the
scattered across its body. Most fishes Length Up to 201⁄2 in like pectoral spines with attached young in tight schools until they reach
are dark above and light beneath—a (52 cm) a length of about 2 in (5 cm).
pattern called countershading that Weight 51⁄2 – 73⁄4 lb mottled body
serves as a means of camouflage. In this (2.5 – 3.5 kg) fleshy
fish, the arrangement is often reversed, Location E. North America Sex Male/Female barbels
with the underside being darker than the Status Least concern
back. Also known as the bugeye
squeaker, it makes sounds, which are
possibly used to communicate with
others of its species.

This common catfish
belongs to a large family
of freshwater fishes found in
North America. Like other
members of the family, it
is valued as a food fish.

SALMON AND RELATIVES 501

Salmon and relatives

PHYLUM Chordata During their lifetime, many species Most galaxiids are small fishes, less that varies from a few months to several
CLASS Osteichthyes of salmon and trout make impressive than 10 in (25 cm) long, with a tubular, years, the fishes mature into adults and
journeys from the oceans (where they live scaleless body. They have a square return to freshwater to spawn, usually
SUBCLASS Actinopterygii as adults) to freshwater rivers (where they tail and, unlike most other fishes in this to the stream where they hatched. To
SUPERORDER Protacanthopterygii spawn). Salmon are well known for their group, no adipose fin. complete the journey, which may be
spectacular leaps up waterfalls as they several thousand miles long, they often
ORDERS 3 make their way upriver. Freshwater pikes Some of the marine fishes in this have to negotiate fast currents or rough
FAMILIES 16 are close relatives of salmon. Salmon, group have unusual adaptations for terrain, requiring them to leap clear
SPECIES 538 life in deep water. The argentinoids, of the water to progress upstream.
for example, include some species Breeding adults usually cease feeding
trout, and pike are native to North with large, tubular eyes that point before beginning their migration. Having
forward or upward (giving good used all their energy on the journey,
America, Europe, and Asia, although the former two have been binocular vision). Other argentinoids they usually die soon after spawning.
have light-emitting organs. How they find their way to their hatching
widely introduced elsewhere. Three other groups of fish are also site is not entirely understood, but the
Life cycle sense of smell and perhaps celestial
considered relatives: freshwater galaxiids, marine smelts or navigation are thought to be important.
Some species in this group complete Not all salmon and trout follow this
argentinoids (which include tubeshoulders and spookfish), and their entire life in either the sea or in type of life cycle: those belonging to
freshwater. However, other species, landlocked populations spend all their
freshwater smelts or osmeriforms (such as capelin and eulachon). including many salmon and trout, life in freshwater.
spend most of their life in the ocean
However, recent work now suggests these 3 groups may be more but move to freshwater to breed, a Some species of galaxiids are also
life cycle described as anadromous. anadromous. The tiny larvae hatch in
closely related to dragonfish and in future may be placed with Males and females spawn in freshwater freshwater and are swept out to sea.
rivers. When the young hatch, they After a few months, they return as
them in a new superorder called Osmeromorpha. grow for a short time in freshwater and juveniles to freshwater, where they
then move out to sea. After a period mature into adults.
Anatomy of prey, most species have a large
mouth studded with many sharp teeth. FISHES
Salmon and their relatives have a The highly predatory pikes have long
slim, tapering body, usually with teeth for seizing prey and an especially
well-developed swimming muscles. large mouth that allows them to
The fins are relatively small, except for swallow prey almost half their own size.
the tail fin, which is usually large and Salmon, trout, and pikes often ambush
powerful, enabling the fishes to swim prey or attack with a burst of speed
and maneuver quickly. Most species over a short distance.
have a small, fleshy fin, known as an
adipose fin, near the base of the tail,
and pelvic fins that are located far back
on the body. Scales in these fishes are
either small or entirely absent. As
carnivores that feed on a wide variety

BREEDING MALES

During the migration to their breeding grounds, the males
of many species of salmon undergo drastic physical
changes. These include the appearance of new colors
and markings. Some species also develop a hump
on their back and elongated hooked jaws. These pink
salmon from the Pacific Ocean are swimming up a
stream in Alaska.

502 BONY FISHES

Esox lucius This powerfully built predator is one spawn as a pair, but either the male or SILENT AMBUSH
of only a few freshwater fish to have the female may take on a new partner
Northern pike a circumpolar distribution across the later. While courting, the male prods the The well-camouflaged northern
whole of the northern hemisphere. The female on her head and pectoral fins pike hunts by lying in wait among
Location North America, Length Up to 41⁄4 ft northern pike is superbly camouflaged with his snout. Female northern pikes waterweeds, bursting out of cover
Europe, Asia (1.3 m) with light markings on its body. Like its grow faster and larger than the males. the instant its prey comes within
Weight Up to 75 lb close relative, the muskellunge (see range. It feeds mainly on other
(34 kg) below), it has a long head with a STEALTHY HUNTER
Sex Male/Female shovel-like snout, a large, slightly forked The single dorsal fin of the northern pike, fishes, but also eats
Status Least concern tail, and a single dorsal fin. Pike generally set well back near its tail, allows it to approach insects, frogs, and
spawn during the day, in early spring prey on the surface of lakes without making crayfishes, as well as
after the ice has melted. They initially any warning ripples. animals swimming on the
surface, such as water voles
dorsal fin and young waterfowl.

head 25 percent
of body length

shovel-like
snout

underslung lower jaw light markings
on dark body

Esox masquinongy putting up a ferocious fight when has melted. A female may pair with Dallia pectoralis
hooked. In common with other pikes, more than one male and can lay more
Muskellunge it has a very large mouth armed with than 250,000 eggs in a single season. Alaska blackfish
sharp teeth, a sloping forehead and This fish is found in heavily vegetated
FISHES Location E. North America Length Up to 6 ft beaklike jaws, and a torpedo-shaped lakes and rivers, generally in warmer Location N.E. Asia, N.W. Length Up to 13 in
(1.8 m) body, which can accelerate very rapidly waters than those inhabited by northern North America (33 cm)
Weight Up to 99 lb with a sudden flick of the tail. It can pikes (see above), although the 2 fishes Weight Up to 13 oz
(45 kg) be identified by the lack of scales may be found in the same habitat and (375 g)
Sex Male/Female on the lower cheeks and gill covers will occasionally even interbreed. The Sex Male/Female
Status Least concern (opercula). A lie-in-wait predator, it resulting hybrids are a robust breed Status Least concern
ambushes and feeds on animals as with strongly barred markings. The
The muskellunge, or “musky,” is the large as muskrats, catching its prey male hybrid is sterile but females are The Alaska blackfish belongs to the
largest member of the pike family, sideways in its mouth, before turning often fertile. The muskellunge is more mudminnow family—a group of fishes
and is notorious among anglers for them around and swallowing them sensitive to habitat changes than that can survive in very cold and
head-first. Muskellunges spawn over the northern pike, so its numbers stagnant water by gulping mouthfuls of
vegetation in mid-spring, after the ice decline first should any change occur. air. They can even survive being partly
frozen in the ice for periods of several
dark markings on light body long head weeks. This species has a slender
body with rounded fins, a blunt head,
large anal fin and a large mouth with a protruding
lower jaw. It is dark green or mottled
brown, and the males develop a red
outline to their fins during the breeding
season. This slow-moving fish feeds on
insect larvae, snails, and smaller fishes,
which it ambushes and hunts with a
darting movement.

Stenodus nelma in 2 different ways: some—for example spring. They remain there until or fourth year. She lays between
in Canada’s Great Slave Lake—are autumn, when they spawn. The female 130,000 and 400,000 eggs. Although it
Sheefish permanent freshwater fishes, which is accompanied by one or 2 males is valued as a sport fish, the sheefish is
remain in their home range to breed, during spawning bouts, which take more important in commercial fisheries
Length At least 5 ft but most overwinter in brackish water place between dusk and nighttime, in Canada, Alaska, and Siberia, where
(1.5 m) or estuaries, and move upriver in and probably occur only every third it is commonly found.
Weight 62 – 88 lb
Location North Pacific, (28 – 40 kg) long, high, pointed
N.W. North America, Sex Male/Female shallow head dorsal fin
E. Europe to N.E. Asia Status Least concern

This large member of the salmon family large mouth anal fin
has a long, broad, and shallow head
and a large mouth with very fine teeth.
As an adult, it feeds mainly on other
fishes, but its young eat insect larvae
and planktonic animals. Sheefishes live

SALMON AND RELATIVES 503

Salmo salar life of between 1 and 4 years, they arrive at their spawning grounds, the
begin their downstream migration to females are plump with eggs, and the
Atlantic salmon the sea. On entering saltwater, they lose males have developed distinctively
their dark color and develop a silvery hooked jaws. The females are known
Location N.E. North Length Up to 5 ft sheen, and for up to 4 years they roam to use their tails to excavate hollows
America, W. and N. (1.5 m) widely throughout the North Atlantic, in gravel, and the males lie alongside
Europe, North Atlantic Weight Up to 99 lb preying on other fishes. At the end of while the females lay eggs. Adult
(45 kg) this period, they begin to become Atlantic salmon may die after spawning
Sex Male/Female sexually mature, and make their way but, unlike other salmon, a large
Status Least concern back to the rivers and streams where number of the adults often survive.
they originally hatched. Like other Emaciated and exhausted, these
The Atlantic salmon is one of the world’s salmon, they are powerful swimmers, fishes make their way back to the EARLY DAYS
most highly prized sport fishes, as well able to leap over almost all obstacles sea, where they feed and recover. At the age of a few months, young Atlantic
as being widely farmed as a source in their way. They rarely feed on their They return to breed again at intervals salmon are known as parr. At this stage, they are
of food. Wild fishes start their lives as upstream journey, and by the time they of one or 2 years. about 6 in (15 cm) long and have distinctive dark
tiny fry—known as alevins—that markings, or “fingerprints,” along their backs.
hatch out among black spots blue-black back
streambed on the side READY TO BREED
gravel. The When they reenter rivers,
fry feed on silvery sheen Atlantic salmon are silvery,
a diet of on body with blue-black backs and
insect larvae black spots along their sides.
and other Their powerful tails enable
small animals, them to leap up waterfalls
and after a freshwater and weirs on their way to
their breeding grounds.

Oncorhynchus gorbuscha Of all salmon, this species spends the least Salvelinus alpinus The Arctic char is the most northerly
time in fresh water and as soon as they of all freshwater fishes. It is found in
Pink salmon hatch, the fry swim downstream and into Arctic char lakes in the Arctic tundra, where it
coastal waters. Spawning adults may spawns during autumn, as well as
Length Up to 30 in breed in coastal streams up to 620 miles Length Up to 38 in in mountains farther south, where FISHES
(76 cm) (1,000km) from the place they were born. (96 cm) spawning takes place in winter. Its color
Location N.E. Asia, North Weight Up to 14 lb Normally metallic blue, with the approach Location N. North Weight Up to 26 lb varies according to its breeding habits:
Pacific, W. North America (6.5 kg) of the breeding season, it becomes America, N. Europe, (12 kg) adults that migrate toward the sea
Sex Male/Female olive-green or yellow, with a distinct red or N. Asia, Arctic Ocean Sex Male/Female become brightly colored during the
Status Not evaluated pink tinge along the sides. The male also Status Least concern breeding season, but landlocked
develops a high humped back and a hook specimens, usually found in lakes, often
large, oval black at the end of the upper jaw. The pink light spots on have bright undersides all year round.
spots on back salmon has a lifespan of 2 years, which dark background The Arctic char is a popular sport fish
means that fishes born in even years and
those in odd years hardly ever interbreed. among anglers in Canada and
Scandinavia.

Oncorhynchus mykiss rainbow trout is a predator, feeding on TROUT FARMING
insects, snails, and crustaceans,
Rainbow trout and—when adult—on other fishes. It In many parts of the temperate
takes most of its food from the bottom, world, rainbow trout are raised
Location N.E. Asia, North Length Up to 4 ft but also rises to the surface for flying in captivity. Some trout “farms”
Pacific, North America (1.2 m) insects—a habit exploited by anglers supply fishes for food but an
Weight Up to 52 lb using artificial flies. Introduced rainbow increasing number raise this
(24 kg) trout often spend their entire lives in fresh trout—a popular sport fish—
Sex Male/Female water, but in their natural habitat, some for angling, using them to stock
Status Not evaluated adults spend part of their time at sea, lakes where they can be caught
returning to rivers to spawn. Compared by line. Farmed trout are fed on
to freshwater rainbow trout, these protein-rich pelleted food, and
migratory adults—called “steelheads” in grow much more rapidly than
North America—grow faster, live longer, they would in the wild.
and are more productive.
This black-spotted member of the
salmon family is one of the world’s tail fin slightly indented hooked snout on male
most widely introduced freshwater
fishes. Originally from rivers and lakes RAINBOW COLORS red band on
west of the Rocky Mountains, it has Freshwater forms of rainbow spawning male
been spread eastward in North trout range from bluish green
America, and to countries as far apart to brown on the back and sides,
as the British Isles and New Zealand, and are white or yellowish on
wherever well-oxygenated, cool water the belly. Spawning males
can be found. Like all its relatives, the develop a vivid red or pink
band on the sides.

504 BONY FISHES

Oncorhynchus nerka their natal spawning rivers, their heads SPAWNING
turn bottle-green and their bodies bright
Sockeye salmon red. Of all Pacific salmon, the sockeye When they reach about 4 years old, all adult sockeye salmon eventually return
salmon is unique because while in some to their native streams to spawn and then die—a final journey that
Length Up to 33 in populations the fry migrate straight down can involve traveling up to 930 miles (1,500 km).
(84 cm) to the sea, most spend their first 1-2
Location N.E. Asia, Weight Up to 15 lb years in lakes within their river’s watershed.
North Pacific, N.W. and (7 kg) The lake-locked form of sockeye
W. North America Sex Male/Female salmon—the kokanee—is typically
Status Least concern one-sixth the weight of its sea-going kin.

Also known as the “blueback” and the JUMPING THE RAPIDS SMALL FRY
“red” salmon, the sockeye salmon The sockeye salmon’s determination to reach its When sockeye salmon fry emerge from the
undergoes a remarkable physical native spawning ground is demonstrated by the gravel, they embark on their first journey
transformation at the time of spawning. dramatic way it launches itself over rapids. to a nearby lake. They will stay there for
Before spawning, sockeye salmon of at least a year before heading out to sea.
both sexes have steel-blue heads and humped
backs and silvery sides. However, back NEW LIFE
between June and September or so, Having reached its spawning ground, the
when they leave the ocean and enter female sockeye salmon digs a nest in the
gravel river bed and lays up to 4,300 bright
spotless dorsal fin pink eggs, which are fertilized by the male.
RIVER GRAVEYARD
After spawning, all sockeye salmon die, their
bodies littering the same stretch of river in
which they themselves were spawned.

FISHES DISTINGUISHING FEATURES bright crimson RETURNING SOCKEYE SALMON
The sockeye salmon has a streamlined body spawning coloration The sockeye salmon is anadromous—living
and a blunt, conical snout. It is distinguished in the sea but entering freshwater systems to
from other salmon species by its fins, which spawn. As the salmon return to their spawning
usually lack definite spots, and its dramatic rivers, the bodies of both males and females
color change at spawning. turn red and their heads turn green; the
male also develops a humped back
and a hooked nose.

CRIMSON TIDE
The spectacular annual run of the sockeye
salmon—sometimes comprising millions of
fishes—is a popular attraction, with viewing
platforms being built across spawning rivers.

505 FISHES

506 BONY FISHES

Coregonus artedi than the females and, during the Thymallus thymallus streams, but is also found in some
breeding season, the males develop cool lakes. Males especially have
Cisco small bumps (pearl organs) that European grayling an unusually long and tall dorsal fin,
function to stimulate the female to lay which they hold erect during spawning
Location N. North America Length Up to 221⁄2 in her eggs. The young feed on algae and Location W., C., and N. Length Up to 231⁄2 in displays to attract females. Grayling
(57 cm) plankton, whereas adults are more Europe (60 cm) feed on a wide variety of swimming
Weight Up to 73⁄4 lb predatory and also feed on insects Weight Up to 14 lb and bottom-living invertebrates, but
(3.5 kg) and small crustaceans. The cisco (6.5 kg) also take insects from the surface;
Sex Male/Female differs from other Coregonus species Sex Male/Female their sporting qualities are appreciated
Status Least concern in having upper and lower jaws of the Status Least concern by fly fishermen. Graylings’ edible
same length and more gill rakers. A flesh smells of the herb thyme. The
Essentially a freshwater fish, the cisco, major threat to this species is the This graceful salmonid, sometimes grayling is a useful indicator of water
or lake herring, may also be found in introduction to lakes of the alewife and called the “lady of the stream”, is a quality because it cannot tolerate
brackish water and very occasionally lamprey. However, it is also sensitive to denizen of fast-flowing rivers and organic pollution nor temperatures
in salt water. It is usually found in large pollution and the recent rapid decline above 68° F (20° C). This means it has
shoals in mid-water, the depth varying of Diporeia, a tiny crustacean that is a disappeared from suitable stretches
with the season. Basically a plankton- major food source to lake fishes. of river in some regions.
feeder, it will also consume a wide
variety of other foods. Spawning OPEN-WATER FISH
occurs in autumn and is dependent This slender, silvery fish has the characterstic
on the temperature of water. dark upper and light lower body of an open-
Males are usually smaller water schooling fish. It also has the fleshy
adipose fin that is typical of the salmon family.

steel-blue back adipose fin

FISHES Opisthoproctus soleatus Bathylagus niger

Barrel-eye Deep-sea smelt

Salmo trutta migrate down into coastal waters Length Up to 41⁄4 in Length 51⁄2 in
after 2 to 3 years as silvery “smolts,” (10.5 cm) (14 cm)
Brown trout later returning to fresh water to Weight Not recorded Weight Not recorded
breed. Populations of brown trout Sex Male/Female Sex Male/Female
are highly variable in their background Status Least concern Status Not evaluated
color and in the number and size
Length Up to 41⁄2 ft of their characteristic spots. Large Location Tropical and Location Southern Ocean
(1.4 m) red and black spots, haloed with subtropical waters
Weight Up to 33 lb white, are common in adults, which worldwide
(15 kg) have a large mouth extending well
Location Northern Europe; Sex Male/Female beyond the eye. Barrel-eyes are relatively small fishes Found between depths of 656 – 5,118 ft
introduced worldwide Status Least concern named for their tubular, upward-facing (200 – 1560 m), this deep-sea smelt was
and underslung lower jaw, but is blue eyes, an adaptation that probably discovered in the Scotia Sea between
Thanks to widespread introductions, to blue-brown above. Adult eulachons helps them hunt other fishes from South America and Antarctica. Its
the brown trout can be found in live at sea, where they feed on below. They belong to the same family habits are little known but it probably
clean, cool, freshwater rivers, streams, plankton, filtering their food from the as the spookfish (see right) and, like feeds on krill—which makes up nearly
lakes, and stocked ponds worldwide, water. However, they travel upstream in them, have most of their fins—apart 50 percent of the food eaten by related
but it is native to northern Europe and medium- to large-sized rivers to spawn. from the pectoral pair—set close to Antarctic species. All Bathylagus smelts
western Asia. While most individuals Few survive spawning, which limits the tail. This fish is dark above and are small fishes of polar waters.
spend their whole lives in fresh water, the fish’s lifespan to between 2 and 4 silvery below, and has a luminescent
some populations, known as sea trout, years. Eulachons are both a sport and a organ on its rectum that contains Dolichopteryx parini
subsistence resource, and when caught light-producing bacteria. The light
in the mouth of rivers are so oily that shines through a lens, and is reflected Winged spookfish
they can be used as wicks for by the fish’s flattened underside, or
Thaleichthys pacificus candles; hence their common “sole,” which spreads along the length Length 81⁄2 in
name “candlefish.” Their oil of its body. This diffused light matches (22cm)
Eulachon used to be traded by native the dim light from the surface, making Weight Not recorded
North Americans; the trade the barrel-eye practically invisible Sex Male/Female
routes were often called from below. Barrel-eyes are found Status Not evaluated
“grease trails.” in tropical waters, at depths between
Length Up to 113⁄4 in about 984–2,650 ft (300–800 m). Location North Pacific
(30 cm)
Location E. North Pacific, Weight Up to 21⁄8 oz barrel-shaped large Belonging to a family of remarkable
W. North America (60 g) eyes dorsal fin “barrel-eyed” fish, this fish was described
Sex Male/Female in 2001 on the basis of a single specimen
Status Least concern from the waters of the North Pacific and
is named for its winglike fins. Since then
This is a member of the smelt family— other specimens have been caught,
a group of slender, silvery fishes that but—like other members of the genus—it
also includes the capelin (see opposite). remains rare. It feeds on invertebrate
Like the capelin, it has a long body planktonic animals, such as free-
swimming crustaceans.

SALMON AND RELATIVES 507

Dolichopteroides binocularis highly unusual anatomy of its eyes. appearing as a bump on the side. Plecoglossus altivelis
Tubular in shape, they point obliquely These diverticular eyes give a 4-eyed
Spookfish upward, like a pair of binoculars. This appearance to the fish. Like many Ayu
would make light directed at the side of deep-sea fishes, the spookfish is
Length Up to 91⁄4 in the eyes hard to detect but each eye is very fragile, and prone to damage Length Up to 28 in
(24 cm) divided into two halves, the second half if recovered from great depths. (70 cm)
Weight Not recorded Weight Not recorded
Sex Male/Female filamentlike Sex Male/Female
Status Least concern pectoral fins Status Data deficient
Location W. North Pacific,
Location Tropical and E. Asia
subtropical waters
worldwide, W. North Atlantic

This bizarrely shaped, slow- transparent large, dark spots The ayu is flattened from side to side,
growing fish is one of white body and has one large and one small dorsal
about 19 species in the fin and a forked tail. A vegetarian, it
spookfish family. It is feeds on river algae with its modified
distinguished from its teeth and digests food with the help of
relatives by its long, an extra-long gut. The ayu’s specialized
filamentlike pectoral fins, which are over kidneys enable it to move between sea
half as long as the rest of its body. and freshwater without being affected
However, its most striking feature is the by the changes in salinity.

Argentina silus silvery sides that have a golden luster. Mallotus villosus it is olive green on the back, merging with
Argentines swim just above the seabed silver on its sides and underside, and has
Greater argentine in deep water, below 492 ft (150 m), Capelin a large adipose fin—one of the
and feed on planktonic (drifting) characteristic features of salmon and
Length Up to 231⁄2 in invertebrates, such as crustaceans, Length Up to 8 in their relatives. Capelin feed on small
(60 cm) squid, and comb jellies, as well as small (20 cm) planktonic crustaceans, pelagic worms,
Weight Over 16 oz fish. Large eyes help the fish spot and and small fish. During the breeding
(450 g) ambush prey in the dim conditions that Weight Up to 17⁄16 oz season, males can be identified by the
Sex Male/Female prevail several hundred meters below (40 g) swollen base of their anal fin and by a
Status Not evaluated the ocean surface. While little is known velvety band of modified scales (villi)
of its natural behavior, the greater Sex Male/Female along the sides of their body. When
argentine is thought to live in shoals courting, the male stimulates the female
Location North Altantic, near the seabed, which would provide Location North Pacific, Status Not evaluated by caressing her with his villi, which FISHES
Arctic Ocean some protection from the many larger induces her to spawn. Capelin migrate
fish that are likely to prey on it. The eggs North Atlantic, Arctic Ocean inshore to spawn on beaches, where the
laid by the female and the fry that hatch female lays up to 60,000 eggs at high
Argentines are marine smelts and are from them, float in mid-water currents The capelin lives and breeds at sea, tide. These are buried in the sand and
also known as herring smelts because between 1,313–1,640 ft (400–500 m). forming large schools that are an subsequently exposed by the action of
they have large silvery scales with tiny The greater argentine is fished for food important source of food for seabirds, the waves. This fish is a major food
spines and superficially resemble in Europe and Russia. seals, dolphins, and whales; in years source for the indigenous populations
herring. The greater argentine has an when capelin numbers are low, seabird of Alaska and Canada.
olive-colored back, white belly, and olive back forked tail fin with rookeries may entirely fail to reproduce.
pointed tips Slender and with a protruding lower jaw, olive green back
sharply
pointed head adipose fin

white belly protruding lower jaw

Lepidogalaxias salamandroides black and acidic, and dries up entirely Galaxias maculatus tail. It has a high tolerance for sudden
in the summer months. Dwarf salinity changes, linked to its life cycle,
Dwarf pencilfish pencilfishes survive during summer by Inanga which is divided between freshwater
burrowing up to 231⁄2 in (60 cm) deep. and the sea. The eggs are laid on
Length Up to 21⁄4 in To facilitate this, they have unusually Length Up to 8 in estuarine plants and hatch when the
(6 cm) flexible backbones that allow them (20 cm) next high tide occurs. The larvae spend
Weight Up to 7⁄8 oz to wriggle through the damp sand. Weight Not recorded up to 7 months at sea, before returning
(25 g) They remain dormant for up to Sex Male/Female to mature in freshwater.
Sex Male/Female 5 months, breathing through their Status Least concern
Location S.W. Australia Status Near threatened skin. Dwarf pencilfishes cannot move Location S. Australia, New
their eyes, because they lack external Zealand, South Pacific, S.
Discovered in 1961, this tiny silver- eye muscles, but they can bend their Atlantic, S. South America
brown fish is a remarkable example of “neck” to look around. At the onset
adaptation to a highly localized habitat. of the breeding season, males mate Also known as whitebait, this
It is found only in the southwest corner with females, and the eggs are fertilized widespread fish of the Southern
of Western Australia, where it lives in inside the female’s body. Each female Hemisphere has a small, slender, almost
small pools of water that lie over peaty lays up to 100 eggs, and the complete cylindrical body, clear olive gray to
sand. Although the water is fresh, it is lifespan of the species is often just one amber above, with a blunt head, and
year. Dwarf pencilfishes feed mainly on dorsal and anal fins set back close to its
the larvae of aquatic insects.

508 BONY FISHES

Dragonfishes and relatives

PHYLUM Chordata Dragonfishes and their relatives are deep- this group have a generally scaleless a nerve. Light is reflected through a
CLASS Osteichthyes sea predators with unusual adaptations for body that is colored black or brown silvery backing and focused through
catching prey, including large, flexible jaws, to match the darkened waters. a lenslike thickening of the overlying
SUBCLASS Actinopterygii sharp teeth, and light-emitting lures. They also However, some species are silvery scale. They either shine constantly, or
SUPERORDER Stenopterygii have luminous organs on their body known or even transparent. flash on and off. Species that live in
shallower water—at depths to about
ORDERS 2 as photophores. This group also includes Many species have light-producing 1,000 ft (300 m)—generally have fewer
organs called photophores. They and weaker photophores, and the
FAMILIES 5 bristlemouths, viperfishes, slackjaws, and share this feature with the lanternfishes light output seems to vary according
(see opposite), although in the to the amount of light received from
SPECIES About 430 snaggletooths. Their names may reflect their dragonfishes the photophores are above. Thus, photophores may hide
generally larger and more numerous. the fishes from predators below
ferocity, but these are relatively small fishes They are usually located along the them by matching the background
illumination from above. Almost all
whose prey consists of other deep-sea fishes and invertebrates. sides and underparts of the species in this group have a light
body or near the eyes. organ at the end of a chin barbel
Some recent analysis suggests that Each is studlike in or a specialized fin ray. This is
shape and used as a lure to attract prey within
dragonfish may belong to a new linked to striking distance.

superorder group, called FEEDING
Dragonfishes, such as this
Osmeromorpha (see p.501). black dragonfish, are impressive
predators. Many species feed
FISHES Anatomy near the surface at night and
move to deeper water to rest
Most of the fishes in this group have during the day. The body is
an elongated body and a relatively illuminated by photophores.
large head. The head usually contains
modified jaws with a very wide gape.
For example, slackjaws have no floor
to their mouth. Viperfishes have an
extra joint in the head that increases
their gape; as the jaw opens, organs
such as the heart and gills are pushed
backward and downward, out of the
way of incoming food. The jaws are
usually armed with numerous
needlelike teeth that are used to seize
prey or to prevent food from escaping.
Apart from viperfishes, the fishes in

Chauliodus sloani This deep-sea fish has a bluish black, the fish also has photophores along its arching ray
elongated body, a large mouth, and body and around its mouth, which help on dorsal fin
Sloane’s viperfish exceptionally long, transparent fangs. entice prey toward its jaws. It spawns all
The largest fangs are slightly barbed, year round. It is one of 9 species in this
Length Up to 14 in and are too big to fit into the mouth— genus of viperfishes, found at great head deeper barbed
(35 cm) instead they protrude outside it when depths in oceans all over the world. than body fangs
Weight Up to 11⁄16 oz the jaws are closed. The dorsal fin has a
(30 g) long, arching ray that acts as a lure, and
Sex Male/Female
Location Tropical, Status Least concern
subtropical, and temperate
waters worldwide

photophores
line both sides

Idiacanthus antrostomus This bizarre, deep-water marine fish has Malacosteus niger The Northern stoplight loosejaw is
a black, snakelike body and extremely unique in having no membranes joining
Pacific blackdragon large teeth that must be rotated to allow Northern stoplight its jaws and tongue—a feature that
the mouth to open and close. Females loosejaw may help it make a rapid strike at prey.
Location E. Pacific Length Female up to are about 40 times larger than males. The head can pivot and the jaws are
15 in (38 cm) To attract prey, the Pacific blackdragon Length Up to 91⁄2 in protractile, which allows it to draw in
Weight Up to 2 oz uses a movable light-producing organ (24 cm) prey—fishes and crustaceans—much
(55 g) located at the end of a barbel that Weight Not recorded larger than itself. While many species
Sex Male/Female protrudes from the front of the lower Sex Male/Female in this family have light-producing
Status Not evaluated jaw. Other photophores run along the Status Least concern organs (photophores) arranged in rows
belly. Blackdragons feed by night, Location Tropical, along the body, the Northern stoplight
mov ing nearer the surface to prey subtropical, and temperate loosejaw has them only around its
waters worldwide mouth and is the only fish to produce
on small fishes and red bioluminescence.
crustaceans. The short, blunt snout
larvae are remarkable scaleless skin
in having eyes set

on long stalks and
intestines that extend
beyond the tail.

movable light-producing organ

LANTERNFISHES AND RELATIVES 509

Lanternfishes and relatives

PHYLUM Chordata Lanternfishes share with dragonfishes (see or blue. Each species has a unique patterns in dark water. The other
CLASS Osteichthyes opposite) the ability to emit light from organs pattern of photophores, which helps fishes in this group are quite different
called photophores on their head and body. groups maintain cohesion in darkly lit from lanternfishes in anatomy and
SUBCLASS Actinopterygii They are sometimes regarded as the deep- waters. Lanternfishes often make behavior. Most have no photophores.
vertical migrations from deep water to Lancetfishes are slender deep-water
SUPERORDER Scolepomorpha, water equivalent of herrings because they are surface waters at night to feed on fishes. They have a large mouth
Cyclosquamata small, swim in large, dense schools, and form plankton, returning to deep water as containing sharp, pointed teeth and
a vital element of deep-water the sun rises. They have large eyes feed on other deep-water organisms.
ORDERS 2 ecosystems by providing and good vision that help them detect These include lanternfishes, and the
FAMILIES 18 lancetfishes make similar daily
changes in light intensity and migrations as they follow their prey
SPECIES About 520 food for many other recognize photophore between deep water and the surface.
Lizardfishes are bottom-living
fishes, and marine predators that hunt by ambush in
tropical and temperate coastal areas.
mammals. Lanternfishes are found in They have many sharp teeth and are
camouflaged to match the color and
great numbers in the middle layers of
texture of the seafloor. Tripodfishes
deep waters off the continental stand on the tips of 3 elongated
fins. They are found on
shelves. Their relatives include the bottoms of deep
ocean basins.
lancetfish and tripodfish, which

live in deep water, as well as

coastal lizardfish, which use

their fins to rest propped up

on the ocean floor.

Anatomy LIGHT PRODUCTION FISHES

All the fishes in this group have thin A lanternfish’s photophores resemble small,
scales—some silvery and others darkly bright studs (a white-spotted lanternfish is
pigmented—that often fall off when shown here). The males and females of
they are caught. Lanternfishes have some species have photophores arranged
bioluminescent photophores on their in different patterns, which helps them
flanks, undersides, and heads, which recognize one another in dark water.
emit light in shades of green, yellow,

Bathypterois grallator Synodus variegatus Myctophum asperum

Tripodfish Variegated lizardfish Prickly lanternfish

Length Up to14 in Facing into the Length 10 – 133⁄4 in Length Up to 23⁄4 in
(36 cm) current, it feeds on (25 – 35 cm) (7 cm)
Weight Not recorded small crustaceans. Weight Not recorded Weight Not recorded
Sex Hermaphrodite Its eyes are very small, Sex Male/Female Sex Male/Female
Status Least concern and its mouth has a Status Least concern Status Least concern

Location Atlantic, large gape, the tip of the Location Pacific, Indian Location North and South
Mediterranean, Indian upper jaw extending back Ocean Pacific, W. and E. Atlantic,
Ocean, W. Pacific beyond the orbit. The Indian Ocean
pectoral fins have an
This fish perches over the seabed With its pointed snout and large mouth, light-producing
by forming a tripod with elongated elaborate nerve supply, this fish’s head looks very much like a organs on body
rays from its pelvic and tail fins. suggesting that they have lizard’s, when viewed from the side.
a sensory function. It often sits on the seafloor, propped
Alepisaurus ferox on its pelvic fins, with its head
deeply forked tail, and a long dorsal fin raised in a very lizardlike fashion. It
Long-snouted that stretches for about two-thirds of its may also bury itself in the sand
lancetfish length, and is held upright like a sail. with only its snout and eyes visible,
The function of this fin is unknown. The and lunge at small fishes passing
Length Up to 91⁄4 ft large mouth has big, pointed teeth for by. The variegated lizardfish has a One of the most numerous of the
(2.8 m) snagging slippery prey. This fish is a slender, tubular body and its brown, deep-sea fishes and an important link
Weight 10 lb useful source of deep-sea specimens orange, or reddish coloration effectively in ocean food chains, lanternfishes eat
(4.5 kg) for scientists, because the fish in its camouflages it against the sea floor. mainly planktonic crustaceans, and are
Sex Hermaphrodite stomach are usually intact. in turn eaten by seabirds, seals, and
Status Least concern larger fishes such as tuna. They derive
elongated dorsal rays their name from the light-emitting organs
on the head and body. The arrangement
Location Pacific, North of these light organs is an important
Atlantic, Mediterranean feature for the identification of the 250
or so species. Differing arrangements of
sail-like larger light organs near the tail indicate
dorsal fin whether the fish is male or female.

This large and distinctive deep-sea
fish has a spindle-shaped,
iridescent body, a

510 BONY FISHES

Codfishes and relatives

PHYLUM Chordata Codfish, or cods, are a large and Grenadiers have a disproportionally fin in some species. Most have a large
CLASS Osteichthyes important group of mainly predatory fish, large head and a body that tapers to mouth that can be extended to suck
which are also vital prey for many larger a thin, pointed, ratlike tail, which gives in prey. They live in the deep sea.
SUBCLASS Actinopterygii species, such as sharks. As well as cod them their alternate names of rattails
SUPERORDER Paracanthopterygii itself, true codfish—from the order or ratfish. They spend most of their Life cycle
Gadiformes—include haddock, hake, time near the seabed, hunting and
ORDERS 5 pollack, and many other commercially scavenging, and are very unfussy A fully mature Atlantic cod can
FAMILIES 24 important species, as well as the feeders. There are several hundred spawn as many as 10 million eggs in
SPECIES About 667 different species around the world a single season and many other large
and they are among the most species of codfish are similarly prolific
widespread deep-water grenadiers. Other successful of all deep-water fish. egg layers. While a few bottom-living
The confusingly named trout-perches codfish species, such as rocklings,
distant relatives in the same superorder include freshwater are found in fresh water in the US. lay their eggs in hidden crevices in the
They are so called because the sea bed, most simply broadcast them
trout-perches and dories. Apart from them, the majority are two true species (in the family into the water. Losses of eggs and
Percopsidae) have a dorsal fin fry to predators are therefore huge.
marine fish with a small number found in fresh or brackish with spines at the front, like that
of perches, and a small adipose fin Establishing exactly where codfish
water. The largest variety is found in the Atlantic, where many on the back near the tail, as trout species spawn is difficult, but it is
do. Grouped with them in the same known that cod and other codfish do
species live and feed just above the sea bed, often in very order (Percopsiformes) are the migrate to local spawning grounds.
specialized cavefishes, which only These are often in the vicinity of
large shoals. Grenadiers are found at depths of least 20,000 ft have vestigial eyes and tiny pelvic shallow, sheltered nursery sites,
fins, or none at all. such as estuaries, where juveniles
(6,000 m) and have been filmed around hydrothermal vents. can grow in relative safety. Cod
Dories (in the order Zeiformes) do and many other codfish are heavily
FISHES Anatomy of the cod family (Gadidae) always not resemble codfish but there is exploited and many stocks have
have 3. Many have a single sensory molecular evidence that shows they been badly overfished, leading to
True codfish typically have a long, barbel on the lower jaw, which helps are related to codfish. They have deep the collapse of some. Little is known
narrow body, with spineless fins that bottom-feeding species detect hidden but thin bodies, which is obvious from about the life cycle of grenadiers.
are supported by soft rays. The paired invertebrate prey. Species such as the side but not easy to see head-on. They produce in the order of 100,000
pelvic fins are positioned well forward hake that feed in mid-water do not The front part of the dorsal fin has tiny, buoyant eggs, which are thought
on the underside, behind the head have a barbel, but have a protruding strong spines, as does the anal (belly) to float up and develop in mid-water.
and right below or forward of the lower jaw and large teeth suitable for
pectoral fins. They have 1, 2, or 3 catching slippery fish and squid.
dorsal fins on their back but members

FRESHWATER RELATIVES

The only exclusively freshwater member of the
Gadiformes order, the burbot is commonly found
in cold rivers and lakes in the northern hemisphere.
It prefers cold water, staying beneath the thermocline.

CODFISHES AND RELATIVES 511

Amblyopsis spelaea Like most cave-dwelling fishes, the Zeus faber approaching its prey head-on and very
northern cavefish has pale skin, is slowly. In this position its ultra-thin body
Northern cavefish completely blind—in this case only John Dory is nearly invisible, and once within striking
vestigial eye tissues remaining under range it shoots its tubelike jaws forward
Length Up to 41⁄4 in the skin—and has a very localized Location E. Atlantic, Length Up to 30 in and sucks in small fish and crustaceans.
(10.5 cm) distribution. It is restricted to the Mediterranean, Indian (90 cm) Rather like freshwater pikes (p.501), it can
Weight Not recorded limestone caves straddling the state Ocean, W., S.W. Pacific Weight Up to 18 lb hang almost motionless in the water but
Sex Male/Female line between Kentucky and Indiana, (8 kg) can dart away at speed if threatened by
Status Near threatened an area of less than 40 square miles Sex Male/Female predators, such as sharks and other large
(100 sq km). It feeds on tiny, cave- Status Data deficient fish. During spawning, females scatter
Location USA (Kentucky, their eggs in batches onto the seabed,
Indiana) dwelling invertebrates, detecting them where they are fertilized by the males.
with the sensory papillae on its head When they hatch, the tiny larvae swim
and body. and drift as they develop in the plankton.
John Dory can live for up to 15 or so
Coryphaenoides acrolepis Also known as rattails or whiptails, With its dinner-plate shape; tall, spiny
grenadiers are the dominant fishes dorsal fin; and black “thumbprint” mark years if they are not caught. Perhaps
Pacific grenadier on the sloping edges of the world’s on each flank, it would be hard to surprisingly, the species makes
continental shelves. Like its 400 or so mistake a John Dory for any other excellent eating and is fished
relatives, the Pacific grenadier has a fish. This solitary species lives by bottom trawling. It is
large, bulbous head, a sharp snout, and near the seabed, hugging the targeted in large numbers
a body that tapers rapidly into a narrow coastline down to around off Africa, but catches are
tail. Its eyes are large, enabling it to see 1,300 ft (400 m) depth. It is now declining indicating
prey on the seabed. The males make a stealth hunter, over-exploitation.
surprisingly loud sounds with the
Length Up to 39 in muscles in their swim bladder. large eyes
(1 m)
Location North Pacific Weight Up to 22 lb
(10 kg)
Sex Male/Female
Status Not evaluated

very large
eyes

long, filamentous, distinctive FISHES
scaly tail thumbprint mark

Merluccius productus Closely related to the Atlantic cod (see Lota lota This long, slender fish is the only cod to
below), the Pacific hake has a similar spend the whole of its life in freshwater. It is
Pacific hake shape, with an elongated body, large Burbot usually a dull, dirty green to brown above,
head, and projecting lower jaw. It is bluish with dark mottling, and yellowish to creamy
Location North Pacific Length Up to 35 in gray on its back, and silvery on its sides. Location N. North Length Up to 4 ft below. The fish hides under tree roots or in
(90 cm) Much like the Atlantic cod, it forms large America, Europe, N. Asia (1.2 m) crevices by day, and is most active at dawn
Weight Up to 11 lb schools and spawns in early spring, when Weight Up to 75 lb and dusk, when it hunts for insect larvae,
(5 kg) the females lay millions of eggs. These (34 kg) crustaceans, and other fishes. It spawns in
Sex Male/Female drift near the surface and are widely Sex Male/Female winter, and does so—unlike most other
Status Least concern distributed by ocean currents. Eaten by Status Least concern fishes—in the middle of the night, and often
marine animals such as porpoises, seals, under the ice.
and swordfishes, the Pacific hake has
been and is still heavily fished by humans.

pointed snout deep notch in fin

Gadus morhua shelf, and usually feeds at 100–250ft CONSERVATION
(30–80m) above areas of flat mud or sand
Atlantic cod and catches prey both from the seabed The Atlantic cod has been heavily
and in mid-water. Other fishes, especially harvested for many years. In the 19th
Location North Atlantic, Length Up to 41⁄2 ft herrings, sprats, and capelin, form its main century, specimens of up to 200 lb
Arctic Ocean (1.4 m) prey. It usually breeds in early spring, with (90 kg) were sometimes caught, but
Weight Up to 55 lb females releasing millions of eggs into the with today’s sophisticated fishing
(25 kg) water. Adult cod migrate extensively and techniques, stocks have shrunk
Sex Male/Female keep together, making them relatively dramatically; fishes weighing
Status Vulnerable easy to catch. over 33 lb (15 kg) are rare.

This large, school-forming fish is one of FULL-BODIED
the world’s most commercially important A long-bodied fish, the Atlantic cod has a bluntly
species. It lives in water over the continental pointed snout, with one barbel hanging from its lower
jaw. Coloration ranges from greenish to sandy brown.

512 BONY FISHES

Spiny-rayed fishes

PHYLUM Chordata Spiny-rayed fishes form the largest Most spiny-rayed fish have angular
CLASS Osteichthyes superorder of fish (Acanthopterygii) ctenoid scales (see p.468), which
accounting for nearly half of all species. Not have a spiny outer edge. However,
SUBCLASS Actinopterygii surprisingly, the fish within this huge group in boxfish the scales are joined
SUPERORDER Acanthopterygii have a remarkable range of shapes, colors, together to form bony, protective
plates, and in pufferfish they are
ORDERS 34 behavior, and specialized adaptations. They extended as stout spines. Other
species, such as Anguilla eels and
FAMILIES 284 vary in size, from tiny gobies 3⁄8 in (1 cm) long, blennies, have lost all or some of
their scales. The most evolutionarily
SPECIES About 14,800 to huge Mola sunfish up to 13 ft (4 m) long and advanced group of spiny-rayed fish
is the perches (or perciforms), which
weighing up to 2.2 tons (2 tonnes) . Spiny- form the largest order of all
vertebrates (with about 2,500
rayed fish are found in almost every body of fresh water, from species). As well as perch,
this group contains many
small desert pools to huge lakes and rivers as well as throughout familiar fish, such as
bass, snappers,
the oceans, from the surface to the deepest depths. mackerel, and
butterfly fish.
Anatomy fin spines and the two superorders
together are also known as spiny-
Spiny-rayed fish have evolved a rayed fish, or Acanthomorpha. Fin
remarkable range of body shapes spines can be modified as weapons
for varying lifestyles. Tuna are of defense and attack. In lionfish and
torpedo-shaped for maximum stonefish, the spines are armed with
swimming efficiency, anglerfish venom glands, and triggerfish use
are flattened top to bottom, and them as wedges in crevices. The
flatfish from side to side, to suit fishing lure of anglerfish is a
a life spent on the seabed. In spite modified fin spine.
of this variability, they share certain
FISHES anatomical features. The most
obvious is that while the fins of all
bony or ray-finned fish (see p.486)
are supported by soft, flexible rays,
spiny-rayed fish also have a variable
number of stiff, sharp spines in
the dorsal fin, and in the anal and
pelvic fins. Some members of the
superorder to which codfish belong
(Paracanthopterygii) may also have

FIN ADAPTATION

These schooling mullet snappers belong to the largest
group of spiny-rayed fishes, the perchlike fishes. These
fishes share the fin structure of other spiny-rayed fishes,
but in many the pelvic fins are positioned level with
the pectoral fins, increasing mobility and improving
their ability to catch prey.

Regalecus glesne extraordinary length protects it against dorsal fin extends crest of long
most predators and has made it the along body length rays on head
Oarfish subject of stories involving sea pelvic fins with
serpents and marine “monsters.” oblique bars oarlike extensions
Length Up to 26 ft This fish has a silvery body with
(8 m) oblique dusky bars, a short,
Weight Not recorded bluish head, and deep red fins.
Sex Male/Female Its dorsal fin runs along almost the
Status Least concern full length of its body, and has long
Location Tropical, rays forming a crest over the fish’s
subtropical, and temperate head. The pelvic fins are attached
waters worldwide just behind its gill cover, and each
consists of a long, single ray,
Although it lives worldwide in tropical with an expanded tip that looks
and temperate seas, this huge, long, like the blade of an oar, which is
ribbonlike deep-sea fish is rarely how the oarfish gets its name.
captured, or even seen alive. Hence Oarfish, along with opahs, may
little is known about its behavior. Its belong in their own superorder of
spiny-rayed fish, called Lamprimorpha.

SPINY-RAYED FISHES 513

Lampris guttatus contrasting, deep red fins. Unlike Trachipterus trachypterus body that tapers rapidly towards its tail,
most fishes, which swim using their tail, ending in a tiny, upturned, fanlike fin.
Opah the opah swims with its pectoral fins, Mediterranean It usually has a pattern of 1 – 4 widely
beating them up and down like a pair dealfish spaced dark blotches on the upper
Length Up to 6 ft of wings. The fins are long and stiff, with body and one or 2 blotches on the
Location Tropical, (1.8 m) a narrow profile that minimizes drag as Length Up to 93⁄4 ft underside; it has no scales. As in the
subtropical, and temperate Weight 160 lb they slice through the water. Despite (3 m) oarfish, its dorsal fin is deep red in
waters worldwide (73 kg) its toothless mouth and large size—the Weight Not recorded color. This carnivore feeds on mid-water
Sex Male/Female maximum recorded weight of a specimen Sex Male/Female fishes and squid, and depends on
Status Least concern is 160 lb (73 kg)—the opah is well known Status Least concern its large size for protection against
as a very efficient predator, energetically predators. Its eggs and larvae are often
pursuing small fishes and squid. It is Location Mediterranean, found in Mediterranean waters but there
found throughout the world but is most E. Atlantic, Indian Ocean, is little information on its reproductive
common in the North Atlantic and C. and W. Pacific behavior. The Mediterranean dealfish
North Pacific oceans. An inhabitant of family contains 11 species; all are rare,
Also known as the moonfish, this large mid-water levels, the opah is taken on A close relative of the oarfish (see and their biology is poorly known.
fish is an oceanic predator. The opah long lines and with gill nets, and is a p.515), this widespread species differs
has large eyes, a silvery blue body— valuable food fish in Hawaii and on the from it not only in being smaller, dorsal fin extends
which is oval and disklike in west coast of the USA. but also in having a full body length
shape—with strongly
long, narrow, pectoral fins
used to “fly” through water

large eyes

dark blotches fanlike
on upperside tail fin
tapering,
silvery body

moderately FISHES
forked tail fin

narrow pelvic fins on belly Myripristis murdjan

Pinecone soldierfish

Cleidopus gloriamaris species has a bioluminescent organ Length Up to 12 in
on the lower jaw—orange during (30 cm)
Pineapplefish the day, glowing blue-green at night— Weight Not recorded
covered by the upper jaw when the Sex Male/Female
mouth is closed. Because this mainly Status Least concern
solitary fish ventures out at night
Length 11 in from the depths of dark caves, curious Location Pacific,
(28 cm) small fishes, crustaceans, and other Indian Ocean
Weight 18 oz invertebrates are attracted by the
Location Indo-Pacific (500 g) glowing organ on its lower jaw, and The pinecone soldierfish lives on rocky many nocturnal fishes, it has large eyes.
Sex Male/Female are caught and eaten. There is and coral reefs, hiding in crevices during The body scales are large, sharp, and
Status Not evaluated only one other genus in this family, the day and coming out at night to feed very rough, and the spines on the fins
the pinecone fish, which has its on plankton, such as crustacean larvae. and gill covers help deter predators.
The pineapplefish gets its name from its bioluminescent organ on the upper It swims with quick, jerky movements, Its red fins are edged with white. The
shape, and from its large, black-edged instead of the lower jaw. The bizarre propelled by a deeply forked tail. Like pinecone soldierfish is capable of
scales, which look like the segments of appearance of the pineapplefish producing a chattering noise, but why
pineapple skin. It belongs to a family makes it extremely popular in the it does this is not known.
of fishes that are protected by bony aquarium trade. However, only a
armor, and by sharp spines on their skilled aquarist is capable of keeping Anoplogaster cornuta as big as itself. This cruising predator
dorsal and pelvic fins. This particular it alive and well in captivity. uses its large teeth to impale its prey,
Common fangtooth which it traps with rapid, lunging
movements. Young common fangtooths
Length 7 in look very different from their parents,
(18 cm) and at one time were mistakenly
Weight Not recorded classified as a separate species. Adults
Sex Male/Female have a brown to black body, head, and
Status Least concern fins, while juveniles are silvery. Adult
Location Tropical, common fangtooths inhabit greater
subtropical, and temperate depths than the young.
waters worldwide
lateral line
Like many deep-sea fishes, the on body
common fangtooth has a small
body and a disproportionately
large head—an adaptation for
eating prey that can be almost

514 BONY FISHES

Hoplostethus atlanticus roughy has an upturned mouth, and Barbourisia rufa skin of the velvet whalefish is also slightly
small teeth arranged in bands. Its body prickly—a characteristic produced by its
Orange roughy is orange-red, although it appears dark Velvet whalefish scales, each of which has a tiny, central
at great depths, which gives it protection spine. Its fins are placed far back along
Length 20 – 231⁄2 in from predators. It is known to have the Length Up to 151⁄2 in its body, suggesting that the fish is an
(50 – 60 cm) longest lifespan among fish, and can live (39 cm) ambush predator that attacks with
Weight Not recorded up to 150 years. Like its close relative, Weight Not recorded a rapid, headlong rush. The fact that
Sex Male/Female Hoplostethus mediterraneus, the orange Sex Male/Female only individual specimens have been
Status Not evaluated roughy is often caught as a food fish, Status Least concern collected suggests a solitary lifestyle.
and is very vulnerable to overfishing. Location Tropical, This species has not been well studied,
Location Atlantic, subtropical, and temperate as few specimens have been collected,
Indian Ocean, W. Pacific waters worldwide but their size suggests that, like many
deep-sea fishes, the velvet whalefish
Mainly found at the This rarely sighted, deep-sea fish has a is found at different depths at varying
edges of continental large mouth, the jaws having many small, stages of its life. Small young fishes have
shelves, or on the of depressible teeth. It is reddish orange, been found in middle depths, whereas
the open ocean appearing black in deep waters, and its older fishes have been brought up from
floor, the orange elongated body has a flabby feel. The the seabed, indicating that this is
where they spend their adult lives.

Photoblepharon palpebratum Thermichthys hollisi Ophidion scrippsae 330 ft (100 m), but some specimens have
been found at over 26,400 ft (8,000 m)—
Flashlight fish Ventfish Basketweave cusk-eel the greatest depth for any fish. Like other
cusk-eels, this North American species
Length Up to 43⁄4 in Length Up to 12 in Length Over 11 in has a blunt head, large mouth, and an
(12 cm) (30 cm) (28 cm) elongated body that tapers almost to
Weight Not recorded Weight Not recorded Weight Not recorded a point. The scales on its body are
Sex Male/Female Sex Male/Female Sex Male/Female arranged in a crisscross pattern, which
Status Not evaluated Status Not evaluated Status Least concern give the species its name. Basketweave
cusk-eels are active only at night; during
Location W. Pacific Location Galapagos Location E. North Pacific the day, they bury themselves in sand
Islands with only the tip of their snout showing.
At dusk, they partly emerge from
FISHES First identified in 1990, this rare fish Cusk-eels are not true eels, but relatives the sand, waiting for small fishes or
is found only around hydrothermal of pearlfishes (see left) and brotulas invertebrates to pass by. These fishes
vents on the deep-sea bed. It has a (see ventfishes, left). The basketweave may also swim along the ocean floor in
short, stout body and a sizable mouth, cusk-eel normally lives at depths of up to search of their food.
but small, poorly developed eyes.
This small, blunt-nosed fish is one of the Like other vent animals, it depends Amphiprion frenatus while other species may have many
best examples of bioluminescence—or for its survival on the bacteria that hosts. It protects itself from the
light production—in the animal world. thrive in the hot, mineral-laden water Tomato clownfish anemone’s stings by the mucus covering
One of only 8 known species of flashlight that gushes out of vents. It is not its body. If the tomato clownfish leaves
fishes, it remains relatively inactive in known whether it feeds on the bacteria Location W. Pacific Length 3 – 51⁄2 in the anemone, it must, on its return,
caves and deeper waters during the directly or on other animals that use (7.5 – 14 cm) reestablish its immunity through a series
day, and moves to shallower areas them for food. The ventfish belongs Weight Not recorded of brief contacts with the anemone, after
over reefs at night, where it feeds on to a family of more than 200 species, Sex Sequential which it can again immerse itself among
small planktonic animals. Individuals known as live-bearing brotulas, which hermaphrodite the stinging tentacles without harm. It
defend small territories on the reef. live both in deep-sea habitats and Status Not evaluated receives shelter from the anemone, and
Symbiotic bacteria, contained in an around shallow reefs. All give birth feeds on plankton floating by and algae
organ under the eye, produce this to live young. growing around the anemone. A family
fish’s bluish-lime light. The light unit usually occupies a single sea
helps it to find prey, startle This small fish, like other anemone. The largest 2 fishes on an
predators, and communicate with anemonefishes, lives with anemone are the male and female that do
other individuals. Using a movable sea anemones in a symbiotic all the spawning; the rest are males, one
black membrane to cover and relationship. It lives only with of which, when the female dies, changes
expose the bacteria, the fish can sex and takes her place. Anemonefishes
signal to others in a shoal. the bulb tip anemone are members of the damselfish family,
(Entacmaea quadricolor)
one of the most colorful
Carapus acus cucumbers. Attracted to them by their groups of fish on
shape and the chemicals that they coral reefs.
Pearlfish release, the pearlfish enters its host,
tail first, through the animal’s anus, and
Length Up to 8 in takes up residence in the body cavity.
(20 cm) After dark, it goes out to feed on other
Weight Not recorded animals, but it may also feed parasitically
Sex Male/Female on its host’s internal organs.
Status Not evaluated

Location E. Atlantic,
Mediterranean

Like most of the other species in its
family, this slim, scaleless, silvery white
fish spends its adult life inside sea

SPINY-RAYED FISHES 515

Sphaeramia nematoptera Opistognathus aurifrons Periophthalmus barbarus animals on the mud surface, and spends
most of its time out of the water. It can
Pajama cardinalfish Yellowhead jawfish Atlantic mudskipper breathe through its skin, which it has to
keep moist. It can crawl on its pectoral
Length Up to 31⁄4 in Length 4 in Length Up to 10 in fins, and also skip and jump across the
(8 cm) (10 cm) (25 cm) mud by quick, flexing movements
Weight Not recorded Weight Not recorded Weight Not recorded
Sex Male/Female Sex Not recorded Sex Male/Female of its body.
Status Not evaluated Status Least concern Status Least concern

Location Indo-Pacific Location Caribbean to Location E. Atlantic
N. South America

red eyes translucent body Mudskippers have tapering bodies, large
heads, and protruding eyes. Like other
mudskippers, this species feeds on small

scattered
spots

yellow Lopholatilus chamaeleonticeps This large, blunt-headed fish belongs
head to a family of over 40 species, all
Great northern tilefish notable for building mounds or
This finger-sized, shallow-water fish tunneling into the seabed. The tilefish
rounded dark waistband lives on the seabed, usually in coral Length Up to 4 ft creates funnel-shaped tunnels that can
tail fin sand and rubble. Found in clear, (1.2 m) be up to 16 ft (5 m) across and 93⁄4 ft
lobes coastal waters, largely in the tropics, Weight Up to 66 lb (3 m) deep. It uses these as a refuge,
it has a bright yellow head, but its (30 kg) and also to attract prey, such as
This strikingly marked tropical fish most notable characteristic—shared Location W. Central Sex Male/Female crustaceans and small fishes. Each
belongs to a family of over 350 species, by other jawfish—is its habit of Atlantic Status Endangered tilefish makes an individual burrow,
almost all of which inhabit coral reefs creating burrows. This fish usually which it enters head-first, and from
or lagoons. Both sexes have a yellow hovers outside the burrow, looking yellow spots on fins which it emerges tail-first.
head, a dark “waistband,” and for prey; it mates inside. The male
scattered spots toward the tail, but incubates the eggs in his mouth, blue-olive
the female is more brightly colored. spitting them out into the burrow back
Males of this species incubate the before feeding.
eggs in their mouths, protecting them FISHES
until they hatch.

Chelon labrosus the surface scum, using its gill rakers Melanotaenia boesemani Peninsula, New Guinea. The color
to filter the more indigestible material. pattern of the males of this species is
Thicklip gray mullet The muscular stomach and long Boeseman’s completely different from most other
intestines make digestion more efficient. rainbowfish rainbowfishes. The head and front
Length Up to 30 in Found in schools in relatively shallow portion are a brilliant bluish gray, while
(75 cm) sea water and estuaries, the thicklip Length Up to 4 in the fins and the posterior are bright
Weight Not recorded gray mullet is popular both as a sport (10 cm) orange-red. There are alternating light
Sex Male/Female fish and a commercial species. It belongs Weight Not recorded and dark vertical bars in between these
Status Least concern to a family of about 80 species and Sex Male/Female 2 areas. Females are less brightly
Location E. North Atlantic, was once considered to be a relative Status Endangered colored and have a shorter dorsal
Mediterranean, W. Black of the barracuda because of similarities fin ray. They lay 100 – 200 eggs.
Sea in the arrangement of the fins. Location N.W. New
Guinea bluish gray
The common name of this front body
fish is derived from its
prominent, thick upper lip. Boeseman’s rainbowfish is only
It feeds on algal material found in the Ajamaru Lakes region
found on the seabed or in the center of the Vogelkop

Leuresthes tenuis shore in large schools. It displays catch the stranded fishes, using only MATING
remarkable breeding behavior: during their hands. The California grunion is
California grunion spring and early summer, schools of thought to feed on plankton and other California grunion beach themselves
grunion strand themselves en masse on microorganisms, possibly capturing between waves of surf and mate on
Location E. North Pacific Length Up to 71⁄2 in the moist sand of beaches to mate—an these tiny organisms by quickly the moist sand. The female creates
(19 cm) extraordinary sight that attracts many projecting its mouth. a shallow depression for the eggs,
Weight Up to 35⁄8 oz spectators. Spawning takes place at and the male wraps himself around
(100 g) night for 2 – 6 days after a full moon, at SINGLE STRIPE the female, fertilizing the eggs as
Sex Male/Female high tide (see panel, right). The hunting A small, slender fish, the California grunion has they are laid.
Status Not evaluated of spawning grunion is a popular sport a silvery blue stripe running the length of its
in southern California. However, only green body, and is silver-white below. It has no
licensed fishermen are permitted to teeth, and its mouth is tubelike when projected.

The California grunion
is one of over 100 species in
the American silverside
family, and like most of its
relatives, lives close to the

516 BONY FISHES

Tylosurus acus beaklike jaws and slender body. It is dark Cypselurus heterurus Anableps anableps
blue or green above and silvery below,
Needlefish and its jaws contain an impressive array Atlantic flyingfish Largescale foureyes
of sharp teeth. To escape predators, this
Length 35 in (90 cm), agile fish may jump clear of the water. Length Up to 16 in Length Up to 121⁄2 in
max 5 ft (1.5 m) While leaping, it may inadvertently spear (40 cm) (32 cm)
Weight Up to 73⁄4 lb boats or even boaters, causing severe Weight Not recorded Weight Not recorded
(3.5 kg) injury due to its size and strength. The Sex Male/Female Sex Male/Female
Sex Male/Female young may defend themselves by floating Status Not evaluated Status Not evaluated
Status Least concern motionlessly on the surface in an attempt
Location W. Atlantic to mimic seagrass and escape detection. Location Atlantic, Location N. South
E. Indian Ocean, Pacific America

The largest member Also known as the four-wing flyingfish,
of the needlefish this coastal species lives in the surface
family, this species waters and feeds on plankton and small
gets its name fishes. Unlike other flyingfishes, both the
from its pectoral and pelvic fins are modified for
“flight.” By opening out these fins, the
Exocoetus volitans FISH OUT OF WATER four-wing flyingfish can glide over long This long-bodied fish has protruding,
distances—up to 655 ft (200 m)—to froglike eyes that are each divided
Tropical two-wing To achieve liftoff, flyingfishes beat escape predators. In order to propel horizontally, allowing it to see above
flyingfish their tails rapidly beneath the itself clear of the water surface, it may the water and below it at the same
water for the initial thrust, then reach speeds of 37 mph (60 kph). The time. This enables the fish to hunt
Length Up to 12 in extend their pectoral fins to lift them eggs have long, adhesive filaments by equally effectively for aquatic insects
(30 cm) clear of the surface. The lower tail which they attach themselves to underwater or flying insects that have
Weight Not recorded lobe continues to oscillate. At full seaweed to avoid sinking. fallen onto the water’s surface. It
Sex Male/Female speed, the fish can glide for up to swims rapidly to escape predators like
Status Least concern 12 seconds. kingfishers and wading birds, and may
jump clear of the water to escape
Location Tropical and predators such as dolphins, billfishes, predatory fishes. Female largescale
subtropical waters and tuna, and may achieve speeds of up foureyes fish can store sperm and so
worldwide to 40 mph (65 kph) in the air. can lay multiple clutches of eggs.

FISHES Despite its name, this fish does not DISTINCTIVE FINS guppy is very variable in color, often
actually fly; instead, it glides over the The tropical two-wing having blotches of blue, red, orange,
water on specially enlarged and stiffened flyingfish is dark blue Poecilia reticulata yellow, and green pigments, as well as
fins (see panel, right). Some species above and silver below. occasional spots, bands, or stripes of
of flyingfishes have 2 pairs of “wings,” Its distinctive, enlarged Guppy black. Such variation is greater in the
consisting of enlarged pectoral and pectoral fins and asymmetrical aquarium fish. Very fertile, females may
pelvic fins (see Atlantic flyingfish, above tail are evident only in adults. Location Caribbean, Length 21⁄4 – 23⁄4 in have over 100 young at a time, although
right) but this species glides on its 2 N. South America (6 – 7 cm) the typical brood is 20 – 40. Adept at
pectoral fins alone. Flyingfishes Weight Under 3⁄16 oz feeding on mosquito larvae, the guppy
use this technique to escape (5 g) has been widely introduced as an agent
Sex Male/Female of mosquito control.
winglike Status Not evaluated
pectoral fins subdued color of
female
protruding
lower jaw

large, evenly A popular aquarium fish, the
curved scales guppy belongs to a family of
more than 300 species that
are notable for bearing live
young. In the wild, the male

Cyprinodon diabolis area of about 215 square ft (20 sq m). Poecilia latipinna almost the entire length of the body.
Water pollution and fluctuations in A close relative of the guppy (see above),
Devils Hole pupfish the water table threaten its survival. Sailfin molly this fish is also a popular aquarium
The smallest of all pupfishes, it lacks species. Although it is generally olive
Length Up to 1 in pelvic fins and the vertical barring Length 1⁄2 – 2 in green, many different color forms have
(2.5 cm) seen in most of its relatives. It breeds (1.5 – 5 cm) been developed. The back, sides, and
Weight Not recorded throughout the year, but rarely lives Weight Not recorded dorsal fin have rows of spots, which may
Sex Male/Female for more than 12 months. Sex Male/Female merge to look like stripes.
Status Critically Status Least concern
Location S.E. USA (Nevada) endangered sail-like
Location S.E. North dorsal fin
America

Found only in a single desert spring The sailfin molly derives
in Nevada, this tiny fish has one of the its name from the
most restricted ranges of any vertebrate. large dorsal fin that
The entire population numbers fewer stands up along
than 500 individuals and occupies an

SPINY-RAYED FISHES 517

Fundulopanchax amieti its very limited range. It is found in Caranx hippos narrow-based, deeply forked tail. The
the stoneless, slow-moving, swampy largest of all jack fishes, it can tolerate a
Amiet’s lyretail parts of rivers in the rain forests of Crevalle jack broad range of salinities. Juveniles, which
Cameroon. The female lays her eggs congregate in large schools, tend to
Length Up to 23⁄4 in on the muddy riverbed toward the end Length Up to 4 ft favour brackish water, while older fishes
(7 cm) of the rainy season. Adult fishes die (1.2 m) are found in deeper water, often cruising
Weight Not recorded after only one year, leaving the eggs Weight Up to 71 lb in pairs. It is an active predator of small
Sex Male/Female dormant until the next rainy season. (32 kg) fishes: when it attacks a school of
Status Endangered The onset of rains stimulates the eggs Sex Male/Female baitfishes at the surface, the commotion
to develop and hatch. The fishes Status Least concern caused can be seen from a distance.
Location W. Cameroon mature in only one month and quickly Location E. and
(lower Sanaga system) repopulate the river. W. Atlantic narrow tail
base
Amiet’s lyretail, or Amiet’s pattern and coloration gives the fish its This fish can be
killifish, remained undescribed common name. Normally a peaceful recognized by its large, The pilotfish is a small or medium-sized
until 1976, perhaps because of eater of algae, the male becomes blunt head, the black fish with a silvery body marked with 6 or
aggressive during courtship and when spot near the edge of 7 black vertical bands. It gets its name
Jordanella floridae guarding eggs. He attracts a female by the gill cover, and the from its habit of swimming just in front of
flashing his red, unpaired fins. After the much larger fishes, such as sharks and
American-flag fish female has laid her eggs, he drives her Naucrates ductor rays. This arrangement seems to benefit
away and guards the eggs until they are both the pilotfish and its host. The
Length Up to 3 in ready to hatch after about a week. Pilotfish pilotfish feeds on scraps and parasites
(7.5 cm) on sharks and, in turn, benefits from the
Weight Not recorded green and orange Length Up to 70 cm protection it gets from the larger fish it
Sex Male/Female mottled body (28 in) “pilots;” it also becomes less visible to
Status Not evaluated Weight Not recorded the smaller fishes on which it preys.
Location S.E. USA (Florida) Sex Male/Female
Status Least concern black bands
This fish belongs to the pupfish Location Tropical,
family—a group of small freshwater subtropical, and temperate
fishes that are particularly waters worldwide
common in the Americas. Like
most pupfishes, the sexes differ FISHES
in color, and the male’s distinctive

Remora remora Shark suckers, or remoras, are easily Coryphaena hippurus FEEDING
identified by the sucking disk above
Shark sucker their head, which they use to fasten Dolphinfish
themselves onto whales, dolphins, and
Location Tropical, Length Up to 34 in large fish. This species is most often Length Up to 7 ft
subtropical, and temperate (86 cm) found attached to sharks. The disk (2.1 m)
waters worldwide Weight Up to 21⁄4 lb enables it to save energy by using the Weight Up to 88 lb
(1.1 kg) swimming power of its host for (40 kg)
Sex Male/Female locomotion and gill ventilation. The host Sex Male/Female
Status Least concern protects it from predators, and provides Status Least concern
food scraps; in return, the shark sucker
gleans parasitic crustaceans from the Location Tropical,
host’s skin and gill cavity. subtropical, and temperate
waters worldwide
spineless
sucking disk dorsal fin

Nomeus gronovii Remarkably, it possesses only limited Also known as the dorado, this The dolphinfish eats mainly fishes,
immunity to its host’s toxins, and blunt-headed fish has a single dorsal but also crustaceans and squid
Man-of-war fish relies on its own swimming agility to fin stretching along almost the whole associated with floating objects. It
avoid being stung. It is known to feed length of its elongated body. It also follows ships and may form small
Length Up to 10 in on the tentacles, so it is arguably a possesses a large, deeply forked tail— groups below floating sargassum
(25 cm) parasite of its host. Adults are believed a characteristic feature of an oceanic and other seaweed.
Weight Not recorded to abandon the relative safety of their species that relies on speed to catch
Sex Male/Female hosts for deep waters. food and avoid being eaten. It has reach speeds of 37 mph (60 kph). This
Status Least concern unusual coloration: a back that is a prized food fish is generally restricted
brilliant metallic blue or green, silvery to waters warmer than 68º F (20º C)
Location Tropical waters sides with a golden sheen, and irregular and breeds in the open ocean.
worldwide rows of dark or golden spots. An Spawning occurs at different times
exceptionally rapid swimmer, it can depending on location.

CAMOUFLAGE COLORATION dark spots
The countershading on its body helps this fish on body
blend both into the dark depths and the well-lit
During its early life, this blue-spotted open sea above,
fish often lives among the stinging making it invisible
tentacles of the Portuguese man-of-war to predators
(see p.540)—a habit that keeps it approaching from
beyond the reach of most predators. above or below.

518 BONY FISHES

Xiphias gladius billfish) have been known to slash into Sphyraena barracuda SOCIAL JUVENILES
and even sink small boats, probably
Broadbill swordfish accidentally. Its chief predators are Great barracuda Adult great barracudas are, by and
sharks, especially the mako and blue, large, solitary cruisers, found
Location Tropical, Length Up to 15 ft and it is sometimes attacked by parasitic Location Tropical and Length Up to 61⁄2 ft typically at or near the surface of
subtropical, and temperate (4.5 m) lampreys. Swordfish spawn in warm subtropical waters (2 m) open tropical and subtropical seas,
waters worldwide Weight Up to 1,300 lb waters throughout most of the year, worldwide Weight Up to 110 lb in warm and shallow waters. They
(590 kg) the months depending on the area. (50 kg) have been caught occasionally at
Sex Male/Female Sex Male/Female depths of 330 ft (100 m). The young,
Status Least concern SOLITARY HUNTER Status Least concern however, sometimes swim in small
groups inshore, in shallow, sheltered
A popular food and game fish, this Adult swordfishes usually hunt alone. The great barracuda is a formidable, reefs and mangrove swamps. This
fast-swimming predator gets its name Like tuna and marlin, they have fast-moving predator, with few natural allows them to hunt in groups and
from its long, flat, swordlike snout similar proportions of the 2 distinct enemies apart from large sharks. Its also provides them with some
(bill). These fish are extremely difficult kinds of swimming muscles: dark large head and powerful jaws conceal protection from predators.
to study in the wild, but fish in the red muscles are used for steady knifelike teeth. This fish remains
stomachs of dead swordfish have cruising, while faster-acting white relatively motionless, then lunges potentially fatal condition caused by
obviously been slashed and the victims muscles are used for short bursts forward quickly to grab its prey. It has toxins that barracudas ingest with
or bits of them swallowed whole as of speed. been known to attack swimmers, often their food.
adults have no teeth. The broadbill causing serious injury. However, these LONG BODY
swordfish is one of a handful of tiny second mishaps have usually occurred in The fish has an elongated
ray-finned fish that can maintain their anal fin murky waters where a human limb or body with a long snout. Its body length and
brain and eyes at temperatures up to shiny jewelry can be mistaken for other associated musculature are specially adapted
59° F (15° C) higher than the surrounding fishes. Attacks have also been reported to produce short, rapid bursts of speed.
water. This means they can stay alert in clear waters when the fish has been
and hunt efficiently even in cold, deep provoked with a spear. It is curious and dark bars
water. Swordfish (or perhaps other will swim up close to divers. The great on upper sides
barracuda is a popular game fish and is
large eyes sometimes eaten, but large individuals
close to can cause ciguatera poisoning—a
mouth
first dorsal fin set far
FISHES broad, flat “sword” projecting from second one
lower jaw

HIGH-FINNED inky blotches
Gray-blue above and almost white below, on lower body
the body of the swordfish tapers to a narrow
tail base. The dorsal and anal fins are
narrow and high, enabling fast turning.

Makaira nigricans CONSERVATION

Blue marlin Game fishing can locally affect
the numbers of this fish, but there
Location Atlantic Length Up to 14 ft EGGS AND LARVAE is a much more serious threat
(4.3 m) A single spawning produces millions of eggs, each in commercial fishing. A number
Weight Over 1,985 lb 1⁄32 in (1 mm) in diameter. These possibly hatch of developing countries, whose
(900 kg) within a week. Eggs and larvae are planktonic. offshore waters abound with this
Sex Male/Female species, exploit the blue marlin as
Status Vulnerable a popular source of food. Due to
their size, adult marlin are generally
The blue marlin is renowned among safe from predators other than
anglers for the way it fights when humans, but juveniles fall prey
caught. Hooked blue marlin breach to other sea fishes such as tuna,
the water surface with extraordinary mackerel, and sharks.
leaps. The largest member of the
billfish family, some individuals can high first streamlined body PATTERNED
weigh over 1,985 lb (900 kg). The dorsal fin This fish is dark blue above
upper jaw forms a large bill, which is with silvery white sides crossed
apparently used to stun or kill prey. by bars made up of blue spots.
The lateral keels at the base of its
tail and the pelvic fins set into bill-like
grooves make this fish a upper jaw
powerful and fast swimmer,
capable of explosive bursts of lateral keels
speed and long-distance travel.
Although blue marlin may stray
to greater depths, they prefer the
warmth of surface waters, where they
feed on other fishes such as mackerel,
tuna, dolphinfish, and squid.

SPINY-RAYED FISHES 519

Anabas testudineus CLIMBING Hippoglossus hippoglossus Now endangered due to overfishing,
the Atlantic halibut is one of the largest
Climbing perch The climbing perch will use the stiff Atlantic halibut flatfishes—a group of over 700 species
spines on its gill covers and pectoral that have a highly distinctive anatomy,
Location S. and S.E. Asia Length Up to 25 cm fins to “walk” from one body of water Location North Atlantic, Length Up to 81⁄4 ft suiting them to life on the seabed. Instead
(10 in) to another if forced to by very poor Arctic (2.5 m) of being flattened from top to bottom,
Weight Up to 150 g water conditions. It can survive out Weight Up to 690 lb like many seabed fishes, flatfishes are
(5 oz) of water for several days at a time. (315 kg) flattened sideways, but habitually lie on
Sex Male/Female SPINY FINS Sex Male/Female one side. The Atlantic halibut lies on its
Status Data deficient This small, stocky fish is uniformly Status Endangered left side, and both its eyes are
gray, olive, or brown. Its fins are positioned facing upward, on its right.
The climbing perch is a small freshwater short, the dorsal and anal fins Compared to most other flatfishes,
fish, adapted to life in stagnant lakes having prominent spines.
and ponds where the oxygen supply Atlantic halibuts are unusually
is often poor. It gulps atmospheric brown body active swimmers, and
oxygen at the surface of the water or often catch other
climbs out to do so (see panel, right). fishes in
In some areas, it buries itself in mud midwater.
in the dry season. The climbing perch
is a popular aquarium species, and is camouflaged
also sold as a food fish. upper surface

spiny and other sea animals that make up its
dorsal fin diet. The eggs of the summer flounder
are covered in oil droplets; when the
Paralichthys dentatus fish spawns, the eggs float up toward
the surface, where they hatch into
Summer flounder ordinary fish larvae. When a larva
reaches about 1⁄2 in (1.5 cm) in length, its
the blind side. The jaws on the eyed Location W. North Length Up to 37 in body becomes flattened and the right FISHES
side act like a siphon, drawing in water Atlantic, E. North America (94 cm) eye migrates to the left side. The larva,
that is free of sand, thereby making Weight Up to 26 lb which lacks a swim bladder, then
respiration more efficient. One of the (12 kg) settles on the bottom.
tastiest flatfish, this is an important Sex Male/Female
commercial species. Status Least concern flattened body

Scophthalmus maximus body width equal nostril that helps it to detect such
to length prey items by their scent. This allows
Turbot the common sole to hunt under the
cover of darkness and to lie still during
Location E. North Atlantic, Length Up to 31⁄4 ft Like other flounders, the the day, hidden by its extremely effective
Mediterranean, Black Sea (1 m) summer flounder can color camouflage. They will also
Weight Up to 55 lb tolerate low salinities frequently bury themselves just below
(25 kg) and often enters the sediment surface with only their
Sex Male/Female estuaries. It is a eyes visible. Common sole spawn in
Status Not evaluated bottom-dwelling spring and summer in local spawning
predator that areas. The young remain in shallow
The almost round body of relies on camouflage, bays and estuaries, which act as
this flatfish has a number speed, and sharp teeth nursery areas. The Wadden Sea—
of bony tubercles scattered to catch the small fishes a UNESCO world heritage site—is
over the surface of the especially important.
upper side. Both the eyes are on Solea solea
the left side, and the mouth is
asymmetrical, with teeth only on Common sole

Pleuronectes platessa the head to the right side, so that the Location E. North Atlantic, Length Up to 28 in
blind left side can lie against the Mediterranean, Black Sea (70 cm)
European plaice seafloor. There, the European plaice Weight Up to 66 lb
feeds on a diet of thin-shelled mollusks (30 kg)
and marine worms. The upper side, Sex Male/Female
capable of rapid and varied color Status Data deficient
changes, camouflages this fish from
Location North Atlantic, Length Up to 31⁄4 ft potential predators. This is the most A commercially important flatfish,
Arctic, Mediterranean, (1 m) important commercial flatfish in Europe. the common sole lives in coastal and
Black Sea Weight Up to 15 lb estuarine environments, where it rests
(7 kg) on sandy and muddy sea beds. Like
Sex Male/Female other flatfish, it is a highly asymmetrical
Status Least concern animal, with both eyes on its colored
right-hand side, which always faces
As a newly hatched fish larva, the upward as it swims or rests. The
European plaice lives for about 6 weeks common sole is carnivorous, feeding
near the surface of the sea. As in all preferentially on ragworms but also
flatfishes, a remarkable transformation taking other worms, and molluscs.
then occurs that turns it into a bottom The blind side has a small tubular
dweller. The left eye migrates across

FISHES 520

SPINY-RAYED FISHES 521

PATIENT HUNTER Epinephelus lanceolatus requires a large food source and takes
The giant grouper usually lurks close to the many years to develop, their density
sea bottom, often lying among coral or rocks, Giant grouper on reefs is extremely limited. They are
until an unwary crustacean or slow-moving easily fished out of entire regions, with
fish swims close by. Capture follows a quick Length Up to 81⁄4 ft little chance of their reappearance
lunge and opening of the cavernous mouth (2.5 m) unless they are strictly protected.
to suck in the prey. Numerous, depressible, Weight Up to 880 lb The giant grouper’s close relation, the
needlelike teeth secure the quarry in the mouth. (400 kg) jewfish or Goliath grouper (Epinephelus
Sex Sequential itajara), is now so scarce that, in US
Location Indian Ocean, hermaphrodite waters at least, it is protected, with all
W. and C. Pacific Status Vulnerable harvesting of it prohibited.

elongated dorsal fin

A dark behemoth of a fish—

one of the largest of the

groupers—the giant

grouper lives in warm,

shallow, coastal waters;

it may also be seen in

estuaries, able to survive rounded
tail fin
in the brackish conditions. small eyes heavy body
Usually solitary, it stays close to

coral and rocky reefs, remaining ROBUST BUILD
largely in the same area, usually around Also known as the Queensland grouper, this
caves and wrecks. The giant grouper fish has a characteristically heavy body and
large mouth. Its typical coloration is brownish,
feeds mainly on crustaceans, with

a favorite food being the spiny with light mottling.

lobster, but it is also known

to eat crabs, a variety

of fishes such as small

sharks and rays, and

young sea turtles.

As juveniles, they are

preyed upon by other fishes, FISHES

but as mature adults, they

are typically at risk only

from humans. Their often

massive size and fairly

sluggish behavior has NOT-SO -GENTLE GIANT
made them an easy The giant grouper is usually easily approached
target of spearfishing. by divers—but some larger specimens are

Since their great size believed to have attacked and killed humans.

522 BONY FISHES

Hippocampus satomie Hippocampus guttulatus Phyllopteryx taeniolatus DRAGON’S EGGS

Satomi’s Long-snouted seahorse Weedy seadragon After mating takes place, the
pygmy seahorse fertilized eggs are attached to the
Length Up to 61⁄2 in Length Up to 18 in wrinkled undersurface of the male’s
Length 1⁄2 in (16 cm) (46 cm) tail and carried around by him. As
(1.4 cm) Weight Not recorded Weight Not recorded the eggs hatch, the baby seadragons
Weight Not recorded Sex Male/Female Sex Male/Female swim away.
Sex Male/Female Status Data deficient Status Near threatened
Status Data deficient tough plates
Location E. North Atlantic, Location S. Australia on body
Mediterranean, Black Sea
Location S.E. Asia it relatively easy
Long-snouted seahorses are remarkable to spot, and it is
fish, with pipette-shaped mouths, The weedy or common seadragon is occasionally sighted
horselike heads, and bodies covered in the open, away from
with bony plates. They feed on planktonic one of the largest seahorses, and one reefs. The leafy seadragon,
animals, and swim upright, propelled Phycodurus eques, has more
by tiny fins. Most species live among of the most bizarrely shaped. Like other elaborate camouflage than this
eel grass and seaweed, and anchor species, and it is less commonly seen.
themselves with their prehensile tails. seahorses, its body is covered with The weedy seadragon searches
Like their close relatives, the pipefish, for small invertebrates, including
they have unusual breeding behavior. toughened plates, but it also has shrimps, among weeds and sponges
In the long-snouted seahorse, the female near the ocean floor. It also feeds on
lays the eggs in the male’s brood pouch, leaflike flaps, which help provide planktonic animals in mid-water.
at the base of his tail. He carries these Numbers of this species are decreasing
until the young hatch. camouflage. Usually found due to indiscriminate collection.

just above the seabed,

the weedy seadragon

hides among seaweed

and plants growing on

rocky reefs. Its bright

coloration—brown to

orange-red with yellow

Described in 2008 on the basis of spotting—does,
specimens collected in Indonesia,
this—the smallest known species of however, make leaflike
seahorse—is a nocturnal inhabitant LEAFY appendages
of coral reefs. At night, it gathers in
small groups on sea fans below reef PROTRUSIONS
overhangs at depths of 49 – 66 ft The weedy
(15 – 20 m). Newborn young are black, seadragon is named
but become paler and browner as they for the leaflike
FISHES grow older—providing camouflage in appendages on its
their coral habitat. body. Unlike other long tail

seahorses, its tail cannot
be coiled around objects.

Aulostomus chinensis The trumpetfish is a common reef Aeoliscus strigatus razorfishes move in synchrony while
predator that often conceals itself feeding on tiny crustaceans drifting in
Trumpetfish by floating with its head vertically Razorfish the plankton. When inactive, they hide
down among the branches of sea head-down among corals and between
Length Up to 32 in fans and other corals. It has a long, Length Up to 6 in the spines of sea urchins. The long,
(80 cm) slender, flattened body, and a small (15 cm) narrow body and elongated snout are
Weight Not recorded mouth at the end of a very long snout. Weight Not recorded adaptations to this lifestyle. The belly has
Sex Male/Female It is generally brown, but some are Sex Male/Female a sharp edge, and that gives this fish its
Status Least concern completely yellow. The trumpetfish Status Data deficient common name. A dark stripe runs along
hunts by ambush, lying motionless the body, and when out over sand, the
Location Pacific, Indian in water like a piece of drifting wood; Location W. Pacific body turns pale for better camouflage.
Ocean it is galvanized into sudden action The body is almost entirely covered
by passing schools of fishes. by thin, transparent plates; only the
This fish spends much of its time underside of the tail region is free of this
long body swimming with its head vertically armor to allow for fin movement.
downwards. Schools of

Scomber scombrus Thunnus thynnus least 43 mph (70 kph). It has a powerful
and streamlined body. Its pectoral and
Atlantic mackerel Atlantic bluefin tuna pelvic fins and its first dorsal fin can be
recessed into grooves to minimize drag.
Location North Atlantic, Length Up to 231⁄2 in Length Up to 14 ft Swimming in schools, the tuna migrates
Mediterranean, Black Sea (60 cm) (4.3 m) as far as 6,250 miles (10,000 km) across
Weight Up to 73⁄4 lb Weight Up to 2,010 lb ocean basins, feeding on open-water
(3.5 kg) (910 kg) fishes. In recent years, overfishing has
Sex Male/Female Sex Male/Female lead to a drastic decline in population.
Status Least concern Status Endangered
finlets
Location Atlantic
crescent-
Atlantic mackerel are streamlined according to size, feeding on fish larvae The Atlantic bluefin shaped tail
predatory fishes that inhabit cold waters and small crustaceans. Spawning occurs tuna is one of the
and continental shelf areas. In spring, from March to June when females lay world’s largest and
they migrate closer to the shore. as many as 450,000 eggs in a season. fastest bony fishes,
Mackerel group in large schools This commercially important species is reaching speeds of at
extensively fished throughout its range.

SPINY-RAYED FISHES 523

Chiasmodon niger able to catch and eat fishes larger than Labroides dimidiatus The cleaner wrasse, an important
themselves. They can do this because member of coral- reef communities,
Black swallower their mouths and stomachs can be Cleaner wrasse feeds on parasites infesting other fishes,
greatly extended to accommodate as well as on their mucus and scales.
Length Up to 10 in prey. Once the contents of the stomach Length Up to 41⁄2 in “Client” fishes queue up at special
(25 cm) are digested, the fishes regain their (11.5 cm) cleaning stations, which are usually
Weight Not recorded normal shape. The black swallower Weight Not recorded occupied by a pair of wrasses or a group
Sex Male/Female lives in the deep ocean but may move to Sex Sequential of females with an adult male. Once the
Status Least concern slightly shallower waters to feed. It has 2 hermaphrodite dominant male dies, he is replaced not
dorsal fins, a long anal fin with a single Status Least concern by another male, but by the dominant
Location Tropical and Location Indo-Pacific female, which changes sex.
subtropical waters spine, and a forked tail.
worldwide dark stripe
hides eye

The black forked tail large
swallower mouth
distended
belongs to a small group of stomach

marine deep-water fishes that are

Echiichthys vipera Heteropriacanthus cruentatus Perca fluviatilis EGG STRINGS

Lesser weeverfish Glasseye European perch Female European perch lay their
eggs in lacelike strings, wrapping
Length Up to 6 in Location Tropical waters Length Up to 20 in Length Up to 20 in them around riverbed stones or
(15 cm) worldwide (50 cm) (51 cm) underwater plants. A single clutch
Weight Not recorded Weight Up to 51⁄2 lb Weight Up to 10 lb can contain up to 300,000 eggs,
Sex Male/Female (2.5 kg) ( 4.5 kg) connected by their sticky mucus.
Status Not evaluated Sex Male/Female Sex Male/Female The eggs hatch in about 2-3 weeks.
Location E. North Atlantic, Status Least concern Status Least concern
Mediterranean and as a sport fish, it has been
The European perch is a freshwater introduced to non-European FISHES
venomous fish that inhabits slow- moving rivers, countries such as Australia. In
dorsal fin This solitary fish gets its name from deep lakes, and ponds. Juveniles feed some places, this has caused
the brilliant reflective layer—called on small planktonic creatures and significant ecological damage.
This venomous fish, frequently found the tapetum lucidum—in its large, invertebrates; adults eat invertebrates
near European beaches, is known to conspicuous eyes. It spends the day and small fishes, such as sticklebacks, dark
inflict painful wounds if stepped upon. under, or near, ridges of rock formations minnows, and even other European stripes
Spines on the first dorsal fin and gill or reefs, emerging only at night to feed perch. Smaller fishes tend to group
cover have poison glands at their on a variety of prey, including small fishes, together, while larger individuals are
bases; if disturbed, this fish erects shrimps, octopus, crabs, and marine more solitary, preferring to lie close
these as a warning, or uses them in worms. Young glasseyes, unlike the to a large rock or among aquatic
defense against larger fishes. This adults, spend their time in the open sea. vegetation. Important both commercially
species spends much of its time buried
in the seabed with only its eyes and STRIPED
the dorsal fin tip exposed. A deep-bodied fish, the European
perch has 2 dorsal fins and
characteristic dark, vertical

stripes, usually 6
in number.

Cromileptes altivelis This small humpback grouper, also
known as the Barramundi cod or
Humpback grouper pantherfish, has very distinctive
coloration, with a whitish head, body,
Length Up to 28 in and fins all covered with small, widely Lepomis cyanellus large breeding colonies, and is found
(70 cm) spaced black spots. Its back rises in groups around aquatic vegetation
Weight Up to 73⁄4 lb steeply behind its head in a “hump.” Green sunfish and shelter. During the breeding
(3.5 kg) Groupers typically change from female season, between late spring and early
Location Indo-Pacific Sex Sequential to male as they get older. Apart from the Length Up to 12 in summer, the male uses his tail to
hermaphrodite fact that it lays eggs, little is known (31 cm) scrape out a shallow nest in which the
Status Vulnerable Weight 35 oz female lays her eggs. The eggs stick to
about the breeding biology (975 g) the gravel bed and the males guard
of this species. Sex Male/Female them and the newly hatched young for
Status Least concern a few days.
Location E. USA
black spots on
body and fins

At home in a wide variety of habitats, large head fins edged in
from sluggish streams to lakes and white or yellow
ponds, the green sunfish is one of
the most common large freshwater
fish in North America. It forms relatively

524 BONY FISHES

Pomatomus saltatrix Sciaena umbra of 283 species. The brown meagre eats Toxotes chatareus
small fishes and seabed invertebrates,
Bluefish Brown meagre usually after dark. Its most notable Spotted archerfish
feature is its ability to produce loud
Location Atlantic, Length Up to 4 ft Length 28 in sounds, used for communication. This Location S.E. Asia, Length Up to 16 in
Mediterranean, Black Sea, (1.2 m) (70 cm) fish also has a sharp sense of hearing. N. Australia (40 cm)
Indo-Pacific Weight Up to 31 lb Weight Not recorded The male brown meagre is known to Weight Up to 1⁄4 lb
(14 kg) Sex Male/Female use the muscles on the highly evolved (21 kg)
Sex Male/Female Status Near threatened swim bladder to make a drumming Sex Male/Female
Status Vulnerable sound as a mating cue. This fish seems Status Not evaluated
Location E. North Atlantic, to have remarkable buoyancy control
Mediterranean, Black Sea
and appears to swim
The sole species in its family, this A deep-bodied fish with a strongly almost effortlessly. Found in brackish water as well as
primitive, perchlike fish has an arched back but a nearly straight
exceptionally wide distribution in underside, the brown meagre arched back in freshwater streams and lakes, this
coastal and estuarine waters across lives in inshore waters. It
much of the world. Known as the tailor belongs to a large family red stripe along its midline, with several deep-bellied, silver and black fish is
in Australia, it has strong jaws and rows yellowish stripes on its lower flanks. It
of razor-sharp teeth, making it a overhanging snout has a downward-pointing mouth and a famous for its ability to “shoot” insect
powerful killing machine. Operating in pair of barbels under the chin, equipped
packs, bluefishes attack smaller with sensory organs that help it find prey off overhanging vegetation, using
baitfishes from behind, often herding food. These barbels, which give the
their prey into tight schools. This fish its other name—the goatfish—are a precisely aimed jet of water of up to
voracious feeder may even eat its own independently movable. They are thrust
young. The bluefish is not territorial, into sand and mud to detect small, 5 ft (1.5 m). It does this by pressing its
and forms large schools that migrate seabed animals—crustaceans, worms,
to warmer waters to mate and spawn. mollusks, and fishes. tongue against the palate, then rapidly
The larvae and young are then
carried back to cooler waters by separated forked constricting its gill chamber. Recently,
ocean currents. dorsal fins tail fin
Mullus surmuletus it has been shown that archerfish squirt
powerful tail
Surmullet jets of water when hunting submerged

prey, such as invertebrates hidden

beneath silt. Juvenile archerfish need

Length Up to 16 in to practise their aim. This fish breeds
(40 cm)
Weight Up to 21⁄4 lb during the wet season, releasing many
(1kg)
Sex Male/Female thousands of buoyant eggs.
Status Least concern
tinted fins spots and
bands on
Location E. North Atlantic, body
Mediterranean, Black Sea

FISHES Highly prized as a food
fish, the surmullet is
reddish in color,
and has a darker

Pomacanthus imperator Chelmon rostratus Oxycirrhites typus

Emperor angelfish JUVENILES Copperband butterflyfish Longnose hawkfish
Young angelfishes have a strikingly different
Length Up to 16 in color pattern; they are dark blue to black Length Up to 8 in Length Up to 5 in
(40 cm) with many concentric, curved to semicurved (20 cm) (13 cm)
Weight Not recorded white lines on their sides. Weight Not recorded Weight Not recorded
Sex Sequential Sex Male/Female Sex Sequential
hermaphrodite Status Least concern hermaphrodite
Status Least concern Status Least concern
Location Indian Ocean, Location Indian Ocean,
Pacific Location Indo-Pacific Pacific

Angelfishes are among the most eye-spot on The 35 species of hawkfishes inhabit
flamboyant inhabitants of coral reefs, dorsal fin
with intense colors and bold patterns tropical waters and are found on coral
that often differ markedly in juveniles elongated
and adults. By appearing completely STRIPES AND MARKINGS snout or rocky reefs. Often resting on sea fans
different, juveniles may avoid being Adults have alternating, yellow and purple
chased by highly territorial adults. The oblique stripes on the body. On the head With their sideways-flattened bodies and black corals, these lie-and-wait
emperor angelfish is a typical species, and around the pectoral fin are light blue, and long, pincerlike snouts, copperband
with a deep body flattened from side to dark blue, and black markings. butterflyfishes are ideally shaped for predators ambush small floating and
side, a small mouth with comblike picking small animals from cracks and
teeth, and a backward-pointing spine single, continuous dorsal fin crevices in coral reefs. This species has bottom crustaceans. It has whitish
on each cheek. Like other angelfishes,
it has the ability, rare among fishes, to 3 orange bands on its sides, and a and red stripes and spots that form a
digest the tough flesh of sponges, narrow black band at the base of its
which are plentiful on coral tail. These striking markings, and the cross-hatch pattern, and an elongated
reefs. This fish sometimes prominent black eye-spot on the dorsal
produces a loud thumping fin, help confuse predators. At night, snout used to pick up prey. This fish is
sound when alarmed. Though the copperband butterflyfish takes on
often seen on their own, males a blotchy coloration to blend in with mostly found on its own, but the male
maintain a small harem of females. the background of the reef.
is territorial. Males court females and

pairs of longnose hawkfish spawn after

sunset in the water a short distance

above the seabed.

long spines red stripes
on single and spots
dorsal fin

525

STICKING TOGETHER

Collared butterflyfishes (Chaetodon collare)
live on reef edges in the Indo-Pacific,
where they feed on coral polyps. They
live in pairs and sometimes gather
together in large schools possibly
for protection from predators.

FISHES

526 BONY FISHES

Maylandia zebra of Africa’s large lakes. It has a small Cetoscarus bicolor Chaenocephalus aceratus
mouth with thickened lips, and scrapes
Zebra mbuna algae from rocks. During breeding, the Bicolor parrotfishes Blackfin icefishes
female picks up her eggs in her mouth,
Length Up to 43⁄4 in and the male then fertilizes them. After Length Up to 35 in Length Up to 28 in
(12 cm) the eggs hatch, the female protects the (90 cm) (72 cm)
Weight Not recorded young for about a week. Weight Not recorded Weight Up to 73⁄4 lb
Sex Male/Female Sex Sequential (3.5 kg)
Status Least concern pale dark, vertical Location Indian Ocean, hermaphrodite Location E. South Pacific, Sex Male/Female
Location East Africa (Lake blue-white fins bars on body Pacific Status Least concern W. South Atlantic Status Not evaluated
Malawi)

This small, metallic blue The blackfin icefish produces a
fish is one of hundreds of natural antifreeze, enabling it to
cichlid species that have survive in the subzero waters of
evolved in the relative isolation the Antarctic. It lacks red blood cells
and this, along with its strong heart,
Astronotus ocellatus Sri Lanka. The oscar, found in South makes circulation easier in cold water,
America, has eye-spots—large, but also gives it a rather pale appearance.
Oscar orange-ringed black spots at the tail It can also absorb oxygen through its
base—that serve to confuse predators. scaleless skin. Its large, toothy mouth
Length Up to 16 in A single spawning contains up to 2,000 Parrotfishes get their name from their and flat head led to it being called the
(40 cm) eggs. Like most cichlids, this species bright colors and bill-like teeth. As these crocodile fish by 19th-century whalers.
Weight Up to 31⁄4 lb tends and guards its young. herbivorous fishes scrape encrusting
(1.5 kg) algae from coral rocks, they also
Location N. South Sex Male/Female remove and ingest part of the rock.
America Status Not evaluated To process this, parrotfishes are also
equipped with upper and lower rows
FISHES The cichlid family is a huge group—of of strong, molarlike teeth in the
perhaps more than 1,600 species – of throat. These help in grinding down
deep-bodied freshwater fish found the rock, transforming it into sand,
mainly in South America, Africa, and which is then defecated. Common
on coral reefs, parrotfishes are major
producers of sand sediments on reefs.

Nemateleotris magnifica in sand or coral rubble on reefs. Its Dissostichus mawsoni creatures from this region, it grows very
slowly, reaching sexual maturity at 8 – 10
Firefish coloration is distinctive, with a pale head Antarctic toothfish years of age. It may sometimes swim up
from the seabed to feed on a range of
and a body that grades smoothly into a small fishes, squid, crabs, and prawns.
Due to its large size, this fish can be
deep orange-red near the tail. Adults eaten only by a few marine animals, such
as sperm whales, killer whales, and
Length Up to 31⁄4 in hover nervously, alone or in pairs, over Length Up to 7 1⁄4 ft elephant seals. The Antarctic toothfish
(8 cm) (2.2 m) does not have a swim bladder, and
Weight Not recorded their burrows, facing the current while Weight Up to 260 lb achieves neutral buoyancy by having
Sex Male/Female (120 kg) light bones and a high body fat content.
Status Least concern feeding on zooplankton. They quickly Sex Male/Female
Status Not evaluated grayish body
dart into the burrows when
is remarkably complex, with the males
Location Pacific, Indian threatened. dorsal fin Location Antarctic Circle building underwater nests for the
Ocean held upright females to enter. When properly
stimulated, the females lay a few hundred
deep orange-red eggs in the nests for the males to fertilize,
posterior and swim out again. The males aerate
the eggs and guard the young.
This palm-sized tropical fish This bottom-dwelling fish can survive
is one of about 80 related in cold Antarctic waters because brownish
species that construct burrows it produces special proteins in green
its tissues and blood that act as back
an antifreeze. Like many

Siganus vulpinus and rocks. A single row of flat, spadelike Gasterosteus aculeatus
teeth enables it to snip off bits of its
Foxface food. Its single dorsal fin has 13 sharp Three-spined
spines. The conspicuous black, white, stickleback
Length Up to 91⁄2 in and yellow coloration may serve to warn
(24 cm) predators that it has venomous fin Length 2 in (5 cm),
Weight Not recorded spines. Males and females have only max 4 in (10 cm)
Sex Male/Female one mate at a time. Weight Not recorded
Status Least concern Sex Male/Female
deep, compressed Status Least concern
Location Indo-Pacific body

Living close to the Location Pacific, Atlantic,
bottom in the shallow Mediterranean, North
water above coral America, Europe, E. Asia
reefs, this brightly
colored fish feeds This widespread, freshwater and coastal
primarily on algae that fish is easily identified by the 3 movable
grow over dead corals spines on its back. Its breeding behavior

SPINY-RAYED FISHES 527

Anoplopoma fimbria Synanceia verrucosa HIDDEN DANGER Scorpaena porcus

Sablefish Stonefish Making the most of its cryptic Black scorpionfish
coloring, the stonefish makes itself
Length Up to 31⁄2 ft Length Up to 231⁄2 in even less conspicuous by scooping Length Up to 16 in
(1.1 m) (60 cm) out a shallow depression on the (40 cm)
Weight Up to 125 lb Weight Not recorded seabed with its pectoral fins. It then Weight Not recorded
(57 kg) Sex Male/Female piles up sand or mud around its Sex Male/Female
Sex Male/Female Status Not evaluated body, and waits for prey. Status Least concern
Status Not evaluated Location E. North Atlantic,
Location North Pacific Location Indo-Pacific dorsal spines Mediterranean, Black Sea

Although it is placed in the same order This fish is a stout, slow-moving The black scorpionfish, or rascasse,
as the scorpionfish, the sablefish predator, with superb camouflage and has a large, bulbous head with large
belongs to a different family that deadly venom produced by glands at eyes and mouth, a brown body with
contains only 2 species. The sablefish the base of its 13 dorsal spines. The mottled markings, and several mosslike
is a widespread, North Pacific fish spines are equipped with sharp tips, appendages between its mouth and
that looks superficially like a cod (see and these can easily penetrate human eyes. It is a sit-and-wait predator that
pp.510), with its long, streamlined body skin, sometimes with fatal results. The lurks among weed-covered rocks, using
and widely spaced fins. Adults stonefish hunts by lying in wait for its its highly effective camouflage to avoid
are blackish to greenish gray above, prey, sometimes half burying itself being seen. All of its fins have rounded
often with blotches or stripes, and in the seabed. When partially margins, and the spines of its dorsal,
have a white underside; juveniles are buried, its upturned head pelvic, and anal fins have poison glands,
blue-black above. Young fishes live and protruding which, when erect, can inflict a harmful
near the ocean surface, usually eyes allow it to sting on its predators.
near coasts, where they feed on locate prey
zooplankton. In contrast, the adults close by. poison glands
live close to the seabed. The sablefish on spines
makes extensive migrations along vertical
coasts, moving to deeper water in mouth tail fin FISHES
winter. It is an ambush predator that
cruises in groups, chasing prey. It SCALELESS FISH
feeds on crustaceans, worms, and The stonefish has
small fishes, such as lanternfishes. an oddly colored,
An important food source, caught in scaleless body which
trawls and traps, and on long lines, the camouflages it very effectively
sablefish is commercially exploited and against the rocky or gravelly seabed.
widely marketed, mostly in Asia.

Cottus gobio Chelidonichthys lucerna Agonus acipenserinus Cyclopterus lumpus

Bullhead Tub gurnard Sturgeon poacher Lumpsucker

Location W. Europe Length Up to 7 in Length Up to 30 in Length Up to 12 in Length Up to 231⁄2 in
(18 cm) (75 cm) (31 cm) (60 cm)
Weight Not recorded Weight Not recorded Weight Not recorded Weight Up to 21 lb
Sex Male/Female Sex Male/Female Sex Male/Female (9.5 kg)
Status Least concern Status Least concern Status Not evaluated Sex Male/Female
Status Not evaluated
Location E. North Atlantic, Location North Pacific Location North Atlantic
Mediterranean, Black Sea

fan-shaped Colored brown to reddish, with a irregular Also called the lumpfish, this stout fish
pectoral fins bony-plated head, the tub gurnard has cirri blotches on body has an adhesive disk, formed from
adapted to life on the seabed. It has 3
wedge- rudderlike tail modified pelvic fins, on its
shaped head isolated, long, and highly mobile underside. This acts as a sucker
The bullhead is a solitary freshwater rays on each of its pectoral fins The sturgeon poacher is one of about and anchors the slow-moving
species that lives under stones or in that act as legs live in shallow water 50 species of poacher, and derives its lumpsucker to rocks and seaweed,
dense aquatic vegetation, where its with strong waves. These fin rays are name, from its sturgeonlike shape. Like allowing it to live in places where the
dark brown, marbled skin provides also highly senstitive and are used to all poachers, it has a large head and current is strong. Found in water up to
excellent camouflage. It feeds on small, probe the seabed for mollusks and elongated snout, and uses its pectoral 1,000 ft (300 m) deep, it swims into
bottom invertebrates, such as insect crustaceans, which, along with fishes, fins like oars and its tail like a rudder to much shallower waters to breed.
larvae. Spawning occurs between form its main diet. The tub gurnard is move along the seabed. All poachers
March and May, depending on the capable of producing grunting sounds also have a distinctive cluster of finely rounded “lumps”
locality. The male excavates a small by contracting the muscles divided barbels, called cirri, that hang body
depression under a stone for the female from their downward-pointing mouths.
to lay her eggs, and guards the eggs associated with its swim bladder. The taste buds on the cirri are used to ARMOR PLATING
until they hatch. These sounds may help probe the seabed for crustaceans and Lumpsuckers get their characteristic knobbly
individuals stay together. small animals. Slow-moving poachers shape from bony plates scattered over the body.
are protected by bony plates. Arranged in rows, these run along the fish’s
blue-marked back and sides.
wing-like
pectoral fins

528 BONY FISHES

Anarhichas lupus the teeth are very well developed: Lophius piscatorius
they are conical at the front of the
Wolf-fish jaws, and molarlike at the back. This Angler
fish uses its teeth and a bony plate in
Location North Atlantic, Length Up to 5 ft the roof of the mouth to crush mollusk Location E. North Atlantic, Length Up to 61⁄2 ft its dorsal fin that can be suspended
Arctic (1.5 m) shells and the carapaces of crabs, Mediterranean, Black Sea (2 m) above its mouth. If anything swims close
Weight Up to 53 lb lobsters, sea urchins, and other Weight Up to 88 lb by, the fish opens its jaws and sucks it
(24 kg) echinoderms on which it feeds. (40 kg) in. The outline of the body is hard to see
Sex Male/Female Spawning takes place in deeper water Sex Male/Female because of the flaps of skin that fringe it.
Status Not evaluated during winter, and the eggs are guarded Status Least concern Spawning occurs between May and
by the male until they hatch. Although August depending on the locality. Each
The wolf-fish is a solitary predator originally caught only as a by-product Also known as the monkfish, the angler female produces up to one million eggs,
that has no pelvic fins and only a of trawler fishing, the delicately flavored is dull greenish brown, with a broad which are released in a gelatinous sheet
rudimentary pelvic girdle. In contrast, flesh of the wolf-fish has led to an and flattened body that tapers rapidly that floats at the surface. The bizarre-
increase in its commercial importance toward the tail. A highly specialized looking larvae that emerge from the
large, broad in recent years. sit-and-wait predator, it is very well eggs mature at different rates; males
head camouflaged and has a fleshy lure on after 4 years and females after 6 years.
small tail
fin marked with white stripes and with a
wide frilly face—was discovered among
Histiophryne psychedelica fishes destined for a public aquarium. In
2008, it was found living among coral
Psychedelic anglerfish rubble in shallows of Indonesian islands.
Each fish has a unique pattern of stripes,
Length 6 in and the fish “walks” on the seabed using
(15 cm) max its pectoral fins.
Weight Not recorded
Sex Male/Female
Status Not evaluated

Location S.E. Asia

FISHES Naso lituratus bright orange spines both in defense Frogfishes are almost spherical-shaped
against predators and as a weapon in anglerfishes, characterized by thick
Orangespine fights for dominance, inflicting deep folded skin and forward-facing eyes.
unicornfish wounds with rapid sideways swipes This distinctive species—pinkish in color,
of the tail. The orangespine unicornfish
Length 18 in has a moderately high, compressed Histrio histrio hence very widely distributed. It hunts
(45 cm) body, but no hornlike projection on prey by using its dorsal fin spine as a
Weight Not recorded the forehead, unlike most other Sargassumfish lure. Sargassumfishes exhibit unusually
Sex Male/Female unicornfishes. It grazes on leafy algae elaborate courtship behavior, with the
Status Least concern attached to the seabed, nipping with Length Up to 71⁄2 in males violently nipping and chasing
its incisor teeth. A valued food source, it (18.5 cm) the females. Except in the spawning
is caught off coral reefs. Weight Up to 14 oz season, adults are highly cannibalistic.
(400 g)
Location Pacific Ocean tail spines Sex Male/Female
Status Least concern
Location Tropical and
subtropical seas
worldwide

The orangespine unicornfish Superbly camouflaged, with leglike
belongs to a family of about highly variable coloring and pectoral fin
82 species known as patterns, this member of
surgeonfishes because of the the frogfish family lives This fish shows an extraordinary
knifelike spine or spines on the among drifting weed and is difference between the sexes. The
side of their tail. This species uses its female (pictured) has a large head and
live in the deep sea, but frogfishes live in Ceratias holboelli mouth, but the male is tiny. When the
Antennarius maculatus shallow water—at depths of only a few adult male finds a mate, he bites into
metres—usually in coral reefs. The warty Kroyer’s deep-sea her flesh, and then lives parasitically
Warty frogfish frogfish’s dorsal fin has a long spine that anglerfish on her. The pair’s blood systems merge
ends in a flap of colored skin, which the so that nutrients flow into the male’s
Length Up to 41⁄2 in fish wriggles to mimic a small fish and Length Female up to body; this bizarre lifestyle is found only
(11.5 cm) so entice prey toward its jaws. 31⁄4 ft (1 m) in deep-sea anglers.
Weight Not recorded Weight Up to 110 lb
Sex Male/Female various spots (50 kg)
Status Not evaluated and patches Sex Male/Female
Location W. Pacific, Indian on body Status Least concern
Ocean
Location Pacific, Atlantic,
This fish belongs to the anglerfish Indian Ocean
order—a group noted for their often
bizarre appearance. Most anglerfishes

SPINY-RAYED FISHES 529

Melanocetus johnsonii dorsal fin. The male has no lure, Diodon holocanthus which are usually folded back, stand
and is less than one-fifth as long as on end. But the spiny armor may
Humpback anglerfish his mate. He attaches himself to Longspined hinder its ability to swim, and it is
the female with his jaws but, unlike porcupinefish often found entangled in nets, much
Length Female up to other deep-sea anglers, swims to the annoyance of fishermen. Brown
Location Pacific, Atlantic, 7 in (18 cm) away after she has spawned. Length Up to 20 in above and yellow below, longspined
Indian Ocean Weight Up to 21 oz (50 cm) porcupinefishes are reef dwellers. Their
(600 g) smooth, Weight Not recorded powerful jaws, armed with fused teeth,
Sex Male/Female scaleless skin Sex Male/Female enable them to crack the shells and
Status Least concern Status Least concern skeletons of many marine invertebrates.

Location Tropical and pectoral prominent
subtropical waters fins eyes
worldwide

This deep-sea anglerfish If threatened, this spine-covered erected
hunts in open water fish swallows large amounts of water, spines
rather than on the seabed. inflating itself until it becomes almost
The female is rounded, spherical, and making its spines,
with an enormous head
and jaws, and a lure on her

Mola mola Balistoides conspicillum

Oceanic sunfish Clown triggerfish

Location Tropical, Length Up to 13 ft ERECT FINS Location Pacific, Indian Length Up to 20 in
subtropical, and temperate (4 m) The triangular dorsal and anal Ocean (50 cm)
waters worldwide Weight Up to 21/4 tons fins are placed far back, and Weight Up to 41⁄2 lb
(2 tonnes) are held erect like a pair of (2 kg)
Sex Male/Female giant blades. This fish moves Sex Male/Female
Status Vulnerable by sculling with these fins. Status Not evaluated

The world’s heaviest bony fish, the almost circular when seen This exceptionally colorful, coral-reef FISHES
oceanic sunfish has a highly distinctive from the side. The young species belongs to a family of fishes
shape. Its scientific name comes from are elliptic in shape. The that can lock their 3 dorsal spines
the Latin for millstone, because it looks oceanic sunfish feeds upright, enabling them to wedge
primarily on jellyfish, themselves into crevices. Its head is
DISK SHAPE using its teeth to nip covered with tough, protective scales,
pieces off prey. Although and its teeth are strong and adapted
Seen in profile, this fish generally slow-moving, to crushing the shells of prey such as
resembles a huge it may jump clear of the mollusks and crustaceans. Like other
disk. Its mouth has water if alarmed. Sunfishes triggerfishes, it can be very territorial,
a padded upper are occasionally seen basking especially during the mating season.
lip, and it has horizontally at the surface; they
small eyes on probably do this only when they white-spotted
either side. are sick or dying. Hugely prolific, they lower body
The tail is breed in the open sea, laying up to
little more than 300 million eggs, which drift away with
a narrow the current. Most sightings of sunfishes
frill attached are in tropical waters, but specimens
directly to are occasionally seen at much higher
the body. latitudes, where currents keep the
temperature relatively warm.

Takifugu niphobles may inflate its body—by pumping water Lactoria cornuta plates under the skin make it a clumsy
into an inflatable sac in the stomach— swimmer and account for its other
Fugu and erect the spines on its sides. The Longhorn cowfish name, the boxfish. This fish hunts by
fugu breeds between May and July, blowing jets of water into the sand on
Length Up to 6 in 1 – 5 days after the full and new moons. Length Up to 18 in the ocean floor to expose the bottom-
(15 cm) Thousands of these fishes arrive to (46 cm) living invertebrates on which it feeds.
Weight Not recorded spawn on pebbly beaches at high tide. Weight Not recorded Longhorn cowfishes are caught and
Sex Male/Female Sex Male/Female dried to sell as ornaments.
Status Data deficient Status Not evaluated

Location W. North Pacific Location Pacific, Indian dorsal fins bony
Ocean, Red Sea toward back projections

Despite the fact that the fugu contains The longhorn cowfish
a poison more potent than cyanide, it derives its name from
is considered a great delicacy in Japan, the small, hornlike
where it and similar fish are prepared. projections above each eye.
To deter predators, this fish may secrete A rigid boxlike casing of bony
its powerful neurotoxin into the water, or it



INVERTEBRATES

532 INVERTEBRATES

invertebrates

Invertebrates are animals that do not have a backbone. Although
many of them are small—and therefore easily overlooked—they
are immensely varied and widespread, accounting for about
97 percent of all known animal species. While
vertebrates form a single phylum, invertebrates
are an informal collection of more than 30, and the
members of just one phylum—the arthropods—
probably outnumber all other animals on earth.
Invertebrates are found in every conceivable type
of habitat, but they are most plentiful in the oceans,
which is where animal life first arose.

I N V E R T E B R AT E S Evolution perhaps as hollow balls of cells similar cases and shells. LIGHTWEIGHT LIFE
to the living colonial proctotist Volvox. Hard body parts Butterflies are typical invertebrates,
Exactly how multicellular invertebrate Infolding or growth of cells inside the fossilize well, so with a small body, a high reproductive rate,
animals evolved remains uncertain, but hollow center would produce simple from this point and a relatively short lifespan. Unlike some
there is little doubt that their ancestors two-layered multi-cellular organisms— onward, the development of vertebrates, invertebrates are ectothermic
were single-celled organisms similar the start of invertebrate life. invertebrate life is much easier to (cold blooded), which means their activity
to living protozoans. One theory, trace. Although it happened long ago, slows down as temperatures drop.
accepted by many biologists, is that The earliest signs of animal life are the Cambrian Explosion brought into
loose colonies of these microorganisms chemical fossils rather than the visible being all the invertebrate phyla that SYMMETRY
formed more permanent partnerships remains of the organisms. Carbon exist today. Studies of living species Adult starfish appear to have radial symmetry,
biomarkers specific to sponges are show that these can be divided into 2 which means that equal body parts radiate from a
large found in rocks dating back about groups: the mollusk-annelid-arthropod central point. A stag beetle has bilateral symmetry,
eyes 700,000 million years. The earliest line and the echinoderm-chordate line. with a body divided in 2 about
fossils of invertebrates themselves The second of these groups gave a single axis. In bilateral
come from late Precambrian times, rise to animals with backbones. animals, many body
about 600 million years ago. At the parts exist in pairs.
start of the Cambrian Period, about Anatomy
545 million years ago, there was an STARFISH
acceleration of evolutionary change, In anatomical terms, invertebrates
known as the Cambrian Explosion. are united principally by things that
Soft-bodied animals, such as jellyfish, they lack: as well as not having a
were joined by ones with hard body backbone, they do not have a bony
skeleton, and they do not have true
PAST SUCCESS jaws. As adults, some invertebrates
Trilobites were among the most successful look like plants, and spend their lives
invertebrates that have ever lived. They existed in one place; others are instantly
for about 300 million years, leaving huge recognizable as animals, because
numbers of fossils, but died out in a mass they are always on the move.
extinction about 245 million years ago.

SKELETONS SHELLS fluid-filled HYDROSTATIC STAG BEETLE
A bivalve shell is a 2-part external cavity
Many invertebrates have a skeleton, which skeleton. It is relatively heavy but SKELETON Despite this bewildering variety,
may be internal or external—examples of exceptionally hard and grows in invertebrates do follow some underlying
both types are found in animals that live in step with its owner. The fluid-filled patterns, particularly on the cellular
water and on land. Some skeletons have body cavity of level. In the simplest kinds, such as
evolved chiefly for protection and can SPICULE SKELETON an earthworm is sponges, individual cells are specialized
withstand powerful impacts, but others are Most sponges have an internal bounded by a but operate as separate units, rather
more flexible and exist mainly to keep the skeleton of mineral slivers flexible wall. The than in groups. Cnidarians are more
body in shape. Skeletons are (spicules), set in a lattice of pressurized fluid acts complex, with similar cells arranged in
made of various materials: protein-based fibers. In this glass like the air inside a tire. tissues. But, in the third and highest
hard structures often sponge, they are arranged with grade of organization—seen in most
consist of crystalline almost mathematical precision. JOINTED SKELETON invertebrates—tissues themselves are
minerals, while the cuticle arranged in organs, and organs into
of insects is made largely Arthropods, such as this pill millipede, have body systems, a pattern that is also
of a plasticlike material an external skeleton made of hard plates. followed in the vertebrate world.
called chitin. Once formed, Joints between the plates make the skeleton
many external skeletons flexible. This kind of skeleton cannot grow. This cellular segregation begins as
cannot grow and have soon as a fertilized egg cell starts to
to be periodically shed divide. In one species of nematode
and replaced.

INVERTEBRATES 533

BACK TO FRONT response. In some of these animals, MIMICRY
such as flatworms, the brain is
Octopuses are bilaterally symmetrical. They have a head with a pair of eyes—one on each side. tiny, but in octopuses and other Mimicry occurs in the vertebrate
Although the arms look as if they are radially symmetrical they are not—they are arranged around cephalopods, it is highly developed world, but invertebrates are the true
the mouth. When an octopus swims, it is the rear part of the body that leads. and can be bigger than that of experts at this form of deception.
some vertebrates. Invertebrates mimic various objects,
worm, the adult body consists of skeleton may be built of hard parts, from pebbles and twigs to bird I N V E R T E B R AT E S
exactly 959 cells. Each one is the but it may also work by fluid pressure Vision is often one of the most droppings, largely to avoid being
product of a precise sequence of cell (see panel, opposite). Known as important senses for invertebrates eaten. They also mimic each other,
divisions and ends up in a location a hydrostatic skeleton, this way of that move. Some of them, such as either as a defense—by resembling
encoded in the animal’s genes. supporting a soft body is found only flatworms, have rudimentary eyes species that are dangerous or
in the invertebrate world. without lenses, which simply detect poisonous—or, more rarely, as a
On a larger scale, one of the changes in the overall level of light. form of camouflage for launching
fundamental differences between Senses But many invertebrates have much an attack. Mimicry is not only
different invertebrates lies in the more complex eyes, equipped with visual: some insects mimic the
symmetry of their bodies. Animals For those invertebrates that are lenses that produce an image. One behavior and even smell of others,
in some groups—such as sea permanently fixed in one place, the form, known as a compound eye, so that they can enter their colonies
anemones—have radial symmetry. sensory world is relatively simple. is widespread among arthropods, and feed on their young without
Their body parts are arranged in the These animals reach out toward including insects. A compound eye being attacked.
same way as the spokes or rim of a anything that gives off the scent of consists of many self-contained units,
wheel, usually with the mouth at the food, and retreat from anything that each with its own receptors and lens UNLIKELY MEAL
center. These animals are often fixed might be a threat. They are sensitive system. Each unit responds to part of A postman butterfly caterpillar’s first line
in place, but if they do move, any part chiefly to dissolved chemicals, direct the field of view, and the total number of defense is its resemblance to bird
of the “wheel” can lead. By contrast, contact, or changes in pressure. These of units determines how much detail droppings. If another animal approaches,
animals with bilateral symmetry usually animals have specialized nerve cells, the animal sees. A smaller number it waves its menacing-looking “horns,”
have a distinct head, which leads the or receptors, scattered throughout the of invertebrates—principally which give off an unpleasant smell.
way when they move. These animals body, and a simple nervous system cephalopods—have eyes that
have an imaginary central dividing line, without a brain. resemble our own. In these, a mate. Unlike vertebrates, invertebrate
which splits them into 2 more or less single lens focuses light onto hearing apparatus is not necessarily
equal parts. This system works well enough for a sensitive surface, the retina, located on the head. Grasshoppers,
organisms that rarely move, but mobile which converts the image into signals for example, have eardrums in their
During the course of evolution, invertebrates need more sensory that travel to the brain. abdomen, while crickets have them
some invertebrates have developed a information. They have more elaborate on their legs. The same is true of
combination of these body plans. Adult nervous systems, with sense organs For invertebrates that live on land, taste organs: flies and butterflies have
starfish, for example, show almost to gather information and a brain to hearing is also a key sense, partly chemical sensors on their feet, which
perfect radial symmetry, except for a process it and trigger the most suitable because it is often used for locating a means they can decide whether
small off-center opening (or madreporite) something is edible simply by
that connects their water vascular TUNING IN sensory standing on it.
system to the outside. A male mosquito’s bushy antennae are used hairs
for hearing. This is an example of hearing Mobile invertebrates also need
Internally, invertebrates show a of a precise kind: the antennae respond to nerve to know about their orientation and
wide range of body plans. Sponges— the exact frequency of the female’s whining motion. Most have gravity sensors,
uniquely in the animal kingdom—are full flight. The frequency used varies from one hollow that tell them which way up they are,
of perforations, or pores. By drawing species to another. cavity and tension sensors that are triggered
water through these pores, they filter when they move body parts such as
out tiny particles of food. Some simple MULTIPLE ATTRACTION statocyst legs and wings.
invertebrates have a baglike anatomy, Attracted by color and airborne DETECTING GRAVITY
with a mouth that leads to a central odors, flies congregate on ripe Bivalves have microscopic sensors that
digestive cavity. This arrangement, fruit. They taste this sugary food respond to the direction of gravitational pull.
seen, for example, in cnidarians and with their mouthparts, and with The sensor consists of a chamber lined with
flatworms, has one major drawback: chemical receptors on their feet. nerve cells that detect the movement of a
indigestible waste has to be ejected mineral weight (known as a statocyst).
through the mouth. Most invertebrates
avoid this problem by having a digestive
tract that runs through the body, in
effect forming a tube. This plan—which
is also found in vertebrates—allows the
digestive system to work like a
production line, with different parts
being specialized for separate tasks.

Although invertebrates do not have
bones, many have a skeleton, which
protects and supports them. The

534 INVERTEBRATES

Although asexual reproduction is METAMORPHOSIS
widespread among invertebrates,
most species use sexual reproduction Most invertebrates change shape as they grow up. This change, known
alone. With vertebrates, sexual as metamorphosis, allows the young and adults to live in different ways,
reproduction almost always involves which can improve their chances of finding food.
a male and female animal pairing up, It also helps species to disperse, because one
but in the invertebrate world things stage—either the larva (juvenile) or the adult—
are often quite different. Animals with can have adaptations that enable it to travel.
both male and female reproductive Metamorphosis may be gradual, or rapid and
organs—known as hermaphrodites— abrupt. In the first type, the young often resemble
are common, and these may either their parents, but in the second, they look completely
pair up, as in the case of earthworms, different. Metamorphosis is controlled by hormones.
or they may fertilize themselves.
BUDDING PARENT EARLY STAGE LATE STAGE pupal
An adult hydra can produce young asexually Even where individual animals case
by developing small buds, which grow into are either male or female, they may DRIFTING YOUNG
new individuals. This parent has grown a reproduce without ever having to wings
single bud, which is now several days old. meet. This apparently paradoxical Sea-urchin larvae have slender spikes that help them showing
Eventually, the young animal will break situation is common among marine through
away and become independent. invertebrates, such as sea urchins, to drift in the plankton. As a larva matures, the spikes
and it happens because these COMPLETE CHANGE
Reproduction animals reproduce by external are slowly absorbed. During the pupa stage,
fertilization. They release their sex a caterpillar’s body is broken
Invertebrates have a wide range of cells into the water, and the sperm down and an adult butterfly
reproductive techniques, and include and egg cells mingle, producing large is formed in its place. The
animals that reproduce both asexually numbers of fertilized eggs. For this change occurs inside a
and sexually. Asexual reproduction form of reproduction to succeed, chrysalis, or pupal case.
usually involves just a single parent. the eggs and sperm must be
I N V E R T E B R AT E S In sexual reproduction, 2 separate released with precise timing, SAFE PASSAGE they have hatched. Many arachnids
individuals are normally needed, which is often achieved With her family crowded on her back, a female carry their young on their back, while
although sometimes a single animal by coordinating with scorpion guards her brood. At this stage, the some freshwater crayfish carry theirs
can simultaneously take on both male the changing phases young have pale, soft exoskeletons—these on their legs.
and female roles. of the moon. darken and harden as they age.
Colonies
Few invertebrates rely solely on On land, most them to ensure that they are not
asexual reproduction, because it can invertebrates use attacked by parasites or by mold. Even if they are cared for, most
lead to problems by creating young internal fertilization, Female octopuses attach their eggs young invertebrates soon
that are genetically identical to one with the male and to rocky recesses on the seabed, disperse to take up life on their own.
another and their parents (see p.30). female pairing up, and and remain nearby, squirting jets of But with colonial species, animals
However, for many species— the male inserting his water over them to keep them clean from the same species remain
particularly sap-sucking insects, such sperm into the female’s and well oxygenated. Invertebrates together, forming permanent groups
as aphids—asexual reproduction is body. This can involve may also take care of their young after or colonies. In a colony, the members
a valuable way of boosting numbers complex courtship displays, are usually closely related to one
when food is in plentiful supply. and sometimes—for example, in another, and they often divide up
Internal parasites, such as flukes, spiders—careful behavior on the part the work needed for survival.
also use asexual reproduction at of the male, who runs the risk of Colonial life is a recurring theme in
certain stages of their life cycle. being eaten by his mate. In the insect invertebrate evolution, and it can take
For them, this way of multiplying is world, some male bugs adopt a less a variety of different forms. In some
particularly important, because their ceremonious approach: they use colonies—particularly in the sea—the
complex life histories mean that each “traumatic insemination,” piercing the members are physically joined, and
individual offspring has a very small female’s abdomen with an organ that may be so highly integrated that they
chance of survival. However, with works like a dart. However, internal look and behave like a single animal.
almost all these animals, sexual fertilization does not necessarily This kind of organization is seen in
reproduction intervenes at some point involve the direct transfer of sperm.
in the life cycle, creating the genetic In some scorpions, for example, the COLONY AFLOAT
variations that allow a species to adapt male produces a packet of sperm,
to changing conditions around them. known as a spermatophore, which A Portuguese man-of-war is an
it fixes to the ground. The male then animal colony, formed by a
NEW LIFE presses the female onto the collection of specialized
Released by a coral polyp, a parcel of eggs spermatophore, forcing it into her polyps that live and
and sperm floats upward. At the sea surface, internal genital chamber, where work together.
the parcel will separate, the eggs and sperm fertilization takes place.
will mingle with those of other individuals,
and fertilization will occur. Parental care

Once a female’s eggs have been
fertilized, most invertebrates leave
their young to develop on their own.
As a result, their young face an uphill
struggle during their first few weeks
of life, and a large proportion fail to
survive. These losses are offset by
the large number of eggs that are
produced. A female starfish, for
example, can release 2.5 million
eggs in 2 hours.

At the other extreme, some
invertebrates are attentive parents.
Female earwigs, for example, remain
with their eggs, periodically cleaning

INVERTEBRATES 535

some hydrozoans, including the Feeding NATURE’S RECYCLERS
Portuguese man-of-war. This animal
looks much like a jellyfish but is Collectively, the world’s invertebrates Dozens of dung beetles clamber over a pile
actually a colony of polyps, one of eat almost everything that is—or once of animal droppings. The beetles feed on
which forms a baglike float (see was—alive. They include herbivores the dung, and they also roll it away
opposite). However, floating colonies and carnivores, as well as a host of and bury it to provide food
are comparatively rare: many more species that feed on dead remains. for their young.
invertebrates—including corals, Their appetites embrace everything
bryozoans, and sea squirts—form that we consume as food, as well herbivores and carnivores alike, “tongue” up to 12 in (30 cm) long, I N V E R T E B R AT E S
fixed colonies, attached to all kinds as some highly specialized mouthparts are often shaped to deal which can be unrolled to drink nectar
of objects, from shells to the seabed. foodstuffs, such as rotting with particular sources of food. from flowers or juices from fruit, while
Individuals in such colonies are usually seaweed, feathers, fur, and Caterpillars bite off and swallow their horse flies have a pair of bladelike
connected to one another through even animal tears. food in substantial chunks, but many jaws that can slice through skin,
joined gut and nerve networks, which other insects have a liquid diet. Moths allowing them to lap up oozing blood.
allow sensory signals to be passed In water, a common and butterflies, for example, are Despite being carnivorous, spiders
from one individual to its neighbors. feeding method among equipped with a coiled proboscis or are also liquid feeders. They have a
invertebrates involves tiny mouth, and feed by pouring
CENTER OF ATTENTION filtering out edible GATHERING FOOD digestive juices onto their prey or
Surrounded by workers, a queen honey bee matter, using body Dwarfed by its load, a leafcutter ant injecting it into its body, and then
controls all the activity in her hive. She does parts that act like a carries food back to its nest. In some parts of sucking up the slurry that results.
this by giving off volatile hormones—called sieve. This way of the world, ants eat as much food as all the
pheromones—that evaporate and spread life supports vast plant-eating vertebrates in their habitat. Given their immense numbers,
throughout the nest. numbers of static many invertebrates have an important
invertebrates that live on the sea ecological impact as they feed.
Invertebrate colonies are less bed or near the shore. In these Earthworms play a key part in
common on land, and the members animals, evolution has crafted filtering
of terrestrial colonies are separate, apparatus out of a wide range of body maintaining the fertility of soil,
rather than joined. They reach their parts: barnacles, for example, use while insects have a major
greatest development in social their legs, while bivalves use their gills. role in pollinating flowers
insects, which include termites, Many of these filter feeders actively and breaking down dead
as well as ants, bees, and wasps. pump water through their filters, to remains. In many habitats,
Despite their apparent independence, increase the size of their catch. For invertebrates have a much
the members of these colonies rely on these animals, pumping often has greater effect than larger
each other for survival, just as much the added advantage animals, but unless they
as if they were fastened together. In that it supplies oxygen as are pests, their activity often goes
each colony, one individual—the well as food. Filter feeding is unnoticed by humans.
queen—normally lays all the eggs, also used by many planktonic
while the role of the other members animals, including krill, which PARASITES
is to ensure that the colony is fed, in turn provide food for baleen
housed, and defended from attack. whales—the largest filter feeders Invertebrates make up the vast majority of the world’s parasitic animals.
of all. Underwater “grazing,” in which
vegetation is scraped from a solid Some—including ticks and leeches—live on the outside of their hosts.
surface, is also common. It is a
technique used by limpets, which Many others, such as tapeworms and roundworms, live internally, feeding
have rows of microscopic teeth, and
also by sea urchins, which have a set on their host’s tissues or on the food that it consumes. External parasites
of 5 calcium carbonate jaws.
can often survive with a single host, but many internal parasites have complex
On land, there is no equivalent
of filter feeding, although some life cycles, involving several different hosts in sequence. These multiple hosts
web-spinning spiders come close
to mirroring this way of life, using often include a vertebrate. Most parasites do not kill their hosts, but parasitoids
their webs to trap airborne animals.
Instead, most terrestrial invertebrates are normally lethal. These animals, which include
have to actively forage for food. The
smallest herbivores—including many many insects, lay their eggs in or near cercaria moves adult fluke
wood-eating species—often burrow the bodies of other animals. to large intestine in human
through their food, a lifestyle that When the young hatch, they and matures intestines
helps protect them from attack, devour the host from inside.
but most predatory invertebrates releases
move around in the open. In LIFE CYCLE OF egg

EATING AT LEISURE A BLOOD FLUKE cercaria burrows
Gripping the 2 halves of a mussel’s shell, through skin
a starfish slowly pries them apart. The human blood fluke is a
It can evert its stomach through a parasitic flatworm that uses
paper-thin aperture between the
mussel’s shells to feed on it.

water snails as intermediate

hosts. Its eggs reach water larva enters body of
via untreated sewage, and snail and produces
produce free-swimming sporocysts
larvae. These multiply
asexually inside snails, free- egg shed
producing another swimming from
swimming stage that cercaria human
attacks humans. host in
sporocyst develops into free-swimming feces
cercaria and leaves snail larva (miracidium)

536 SPONGES

Sponges MARINE SPONGES

PHYLUM Porifera Sponges, which were once thought to Most sponges are found in environments with stable
CLASSES 3 be plants, are believed to be Earth’s first temperature regimes. Like the elephant-ear sponge
ORDERS 24 animals. Unlike most animals, which (Lanthella basta) shown here, they are often found on hard,
move through their habitat, sponges rocky surfaces, where they may dominate large areas of
the sea bed. They are especially common in caves.

FAMILIES 127 are immobile, living attached

SPECIES About 10,000 to solid surfaces and

feeding by setting up

currents of water from which they filter

out particles of food. In other words,

their aquatic environment is made

to move through their body rather

than the other way around. Most

sponges are marine animals,

although some species have

adapted to life in freshwater.

Anatomy osculum

I N V E R T E B R AT E S The body of a sponge lacks central cavity Feeding
many features typical of other collar cell
animals. Although the cells spicule Sponges are remarkably effective
perform specialized functions, pore flagellum filter feeders. The cells lining the
they do not form true tissues or body’s inner surface are known as
organs, and there are no nerve collar collar cells, each consisting of a ring
and few muscle cells. However, (or collar) of tentacle-like structures
sponges do have a skeleton— SIMPLE SPONGE COLLAR CELL surrounding a whiplike feature CARNIVOROUS SPONGE
a network of organic collagen called the flagellum. Movement
fibers and inorganic structures BODY SECTION of the flagella creates the current of Found on deep-sea bottoms and in
(called spicules) made of silicon water that moves through the body. Mediterranean caves, this unusual
dioxide or calcium carbonate. Water enters a simple sponge through minute As the water passes through, sponge catches live prey on hooklike
Sponges have no system of pores in the outer surface. It then passes plankton and particles of organic spicules at the end of long filaments
symmetry, nor do they have into a central cavity before being expelled matter are trapped in the collars. and digests it externally.
clearly distinct body parts. The through a larger aperture (the osculum).
simplest sponge is essentially
a tube, closed at one end, but
complex sponges take on many
forms, from crusts, spheres, and
barrels to tangled branches.

Class Calcarea Class Hexactinellida Class Demospongiae

Calcareous sponges Glass sponges Demosponges

Occurrence c.650 spp. worldwide; in shallow water (in Occurrence c.500 spp. worldwide in deep cold water; Occurrence c.7,200 spp. worldwide; in shallow and
crevices, overhangs and caves, on reefs and on seaweed) mostly at depths of 650 – 6,000 ft (200 – 2,000 m) in seas deep water, on solid surfaces of all kinds

These are the only sponges that have Most glass sponges are less than 31⁄4 ft These sponges make up nearly 90 CARIBBEAN PINK VASE SPONGE
skeletal spicules made of calcium (1 m) high but in some areas many grow percent of all sponge species, and Many demosponges form irregular masses, but
carbonate, the mineral that mollusks use together to form “sponge reefs” up include the familiar bath sponge, whose many others are funnel- and vase-shaped like
to make their shells. Compared to other to 65 ft (20 m) in height. Their siliceous populations are now badly affected by Niphates digitalis (above). Up to 12 in (30 cm)
sponges, they are mostly small—less spicules are usually fused together to overcollection. Demosponges vary in size tall, it has, like most demosponges, a skeleton
than 4 in (10 cm) high—lobe- or tube- form rigid, often beautiful, glasslike from less than 1⁄3 in (1 cm) to well
shaped and drab, but some reef species masses. These structures are fragile, over 31⁄4 ft (1 m) in height or breadth, and of siliceous spicules and
are brightly colored. however, and the skeletons of the are often brilliantly colored, creating collagen fibers.
species living in deep water tend underwater “gardens” that rival corals tube open
LEUCETTUSA LANCIFER to collapse when they are for their vivid hues. While crusts and at top
This flask sponge, less than 2 in (5 cm) high, dredged up and brought mounds are common, these sponges
has the classic compound vase shape of to the surface. come in a variety of shapes—some
calcareous species. Members of the genus even bore into mollusk shells, leaving
are widespread in shallow waters from the VENUS’ FLOWER BASKET them riddled with pin-sized holes.
tropics to the subantarctic. Glass sponges are often objects of
remarkable beauty. Species in the STOVE-PIPE SPONGE wall punctured
genus Euplectella, such as the one Aplysina archeri, or stove-pipe sponge, can reach by pores
shown here, are found in tropical a length of over 20in (50cm). In sponges with
oceans below a depth of about this kind of shape, water is drawn in through
500 ft (150 m). They pores in the sides of the tube, and expelled
grow up to 12 in through an opening at the top.
(30 cm) tall.

CNIDARIANS 537

Cnidarians Locomotion

Cnidarians can change shape by

coordinating the contraction of some

PHYLUM Cnidaria This group of simple aquatic animals includes of their muscle cells. In polyps, the water
CLASSES 6 sea anemones, corals, jellyfish, and hydroids.
ORDERS 24 The radially symmetrical body is essentially a tube inside the body cavity can act in a similar
FAMILIES 300 that is closed at one end and open at the other.
way to a skeleton, providing a resistant

structure against which the cells are

SPECIES About 11,000 This tube is either flattened into a bell shape contracted. A polyp can lengthen, bell fully relaxed,
shorten, or bend its body—for ready to push
example, to reach toward potential forward

(a medusa) or elongated with the closed end prey or to retreat from predators.

attached to a hard surface (a polyp). In general, medusae swim freely, By alternately relaxing and

contracting groups of muscle

while polyps live on the seabed. All cnidarians have tentacles around cells, free-living medusae such

their mouth that contain stinging cells, known as cnidocytes. Most as the jellyfish (shown right)

can move using a weak form

species are marine, although a small number are found in freshwater. of jet propulsion. bell begins to
elastic bell relax to take
Anatomy contracts in water
to expel
Some cnidarians (such as sea anemones water JELLYFISH MOVING
and corals) exist only as polyps. Others Jellyfish propel themselves through
(hydroids and some jellyfish) exist as water by contracting their bell, obtaining
both polyps and medusae at different
stages of their life cycle. In both forms, lift from the water being forced out from
the wall of the body tube consists of just
2 layers of cells: an outer epidermis and under the bell. The bell then relaxes, water
an inner gastrodermis, separated by
a jellylike matrix (the mesoglea). The re-enters, and the cycle is repeated.
central cavity of the tube acts as a gut,
and the single opening is used both to I N V E R T E B R AT E S
take in food and to expel waste. Around
the mouth, the body wall is drawn out
into one or more whorls of tentacles.
These contain the stinging cells,
cnidocytes, which are unique to
cnidarians. Cnidocytes inject venom
into prey and hold it while the
tentacles draw it into the mouth.

gastrodermis tentacle POLYP Colonies REEF BUILDING
cnidocytes The mouth of a Many corals are host to algae that contribute
mouth polyp faces outward. At Most cnidarians can reproduce asexually (without mating) by to their metabolism and nutrition. This
gut the opposite end of the body symbiotic relationship allows the corals to
mesoglea is a basal disk, which producing buds from their own body. In some cases, the new grow quickly enough to accumulate the
epidermis is often attached to a solid material to form reefs.
gastrodermis surface. Many polyps, such polyp splits completely; in others, the budding is incomplete so
basal disk as this hydra, do not have CONSERVATION
a well-developed mesoglea. that several individuals remain joined together to form a colony.
velum (shelf of Polyps may occur either Several dozen cnidarian species
muscle) singly or in colonies. Colonies can reach great size, as, for example, in reef-forming (mainly corals) are listed as
vulnerable and some that form
epidermis MEDUSA corals. Some planktonic colonies are highly complex. For coral reefs are now endangered.
mesoglea The body of a medusa looks Threats include rising sea
like a bell, with the mouth at example, colonies of siphonophores consist of polyps and temperatures—as a result of global
gut the center of the lower surface warming—discharge of silt in coastal
mouth and the tentacles at the edges. medusae integrated into what appears to be an individual areas, and collection for souvenirs.
The mesoglea is thicker than If the sea temperature rises above a
tentacle it is in most polyps. Some organism, with specialized certain level, the corals’ symbiotic
medusae have a shelf of tissue algae are expelled, and the corals
that is rich in muscle cells polyps forming the become bleached and often die.
and used in locomotion.

nematocyst CNIDOCYTES polyp projecting equivalent of
coiled thread above hard organ systems.
epidermal cell Each cnidocyte contains a skeleton
BEFORE DISCHARGE bulblike structure, called
uncoiled a nematocyst, which houses connecting CORAL POLYP
hollow a coiled, barbed thread. sheet between
thread When triggered by touch 2 polyps The polyps in a coral colony
or chemicals, the thread secrete an exoskeleton of hard
barbs explodes outward and cup calcium carbonate, which may
AFTER DISCHARGE pierces the victim’s skin. accumulate over time to form
The tentacles are then exoskeleton a reef. The exoskeleton includes
used to pull the prey in. structures called cups, into which
the polyps can withdraw.

538 CNIDARIANS

Class Anthozoa responsible for building coral reefs, the SEA FANS
biggest structures in the living world. Growing 93⁄4 ft (3 m) or more high, sea
Anthozoans These are formed by the animals’ fans such as Annella mollis (left)
external calcareous skeleton. Other occur widely, but are especially
Occurrence About 7,000 sp. worldwide; on the seabed, widespread anthozoans include common in tropical seas.
in soft sediments soft-bodied sea anemones, plus sea They attach themselves
pens and sea fans that have flexible, to hard surfaces by
The word “anthozoa” means “flower horny internal skeletons. creeping rootlets, and
animal,” and with their bright colors, have a tough but
waving tentacles, and fleshy trunks, polyps connected by flexible stem, with
these animals often look remarkably like soft external tissue many branches
plants. However, they are carnivorous— that bear polyps.
as are all cnidarians—although some fanlike
species supplement their diet with mass
food produced by microscopic algae
harbored in their bodies. Anthozoans flexible stem
vary greatly in size, ranging from minute SEA PENS
species less than 1⁄32 in (1 mm) across, With a central axial polyp bearing many lateral polyps, quill-like
to those over 33 ft (10 m) across. When often on regularly arranged side branches, sea pen shape
adult, they form polyps—simple, tubular
animals with the tube closed at one end colonies—found throughout the world—look like old-
and open at the other. The open end is fashioned feather quills. The lower end of the axial polyp
drawn out into one or more whorls of anchors the colony to the seabed. The Pennatula species on
tentacles containing stinging cells, used the right grows to 20 in (50 cm) high,
for feeding and for defense against lateral but some are double this size.
predators as varied as gastropods, polyp Some of the secondary polyps
polychaetes, sea spiders, and starfish.
Anthozoans multiply asexually and of sea pens—such as the
sexually. Many species are solitary, but Pteroeides species on
this group also includes colony-forming BUSHLIKE SOFT CORALS the left, which grows
hard corals—animals that are The fleshy masses of most soft corals contain to 12 in (30 cm) —
calcareous structures (sclerites) that support them. In pump water through
the bushlike species (above), the sclerites may protrude the colony.
when the colony is expanded. A member of the genus
I N V E R T E B R AT E S Dendronephthya, this Indo-Pacific coral grows to 31⁄4 ft axial polyp
(1 m) high. Soft corals like these are either attached
to hard surfaces or anchored in soft sediments.

body envelopes
prey, such as fishes

SEA ANEMONES long, snakelike base of axial
Unlike most anthozoans, sea tentacles polyp used for
anemones live as solitary anchoring
polyps; many of these,
COMMON DEAD MAN’S FINGERS FALSE CORALS however, reproduce by
Soft corals—members of the order Alcyonacea— Living in tropical waters worldwide, false corals are intermediate dividing and forming clones.
occur in all oceans. The North Atlantic species in form between true corals and sea anemones. Their polyps closely The snakelocks anemone,
Alcyonium digitatum (above) grows up to 8 in resemble those of corals, but lack an external hard framework. Anemonia viridis (right),
(20 cm) high, and lives in shallow water. Its polyps Like reef corals, they have symbiotic algae that supply them has tentacles up to
protrude from a white to pink or orange, fingerlike with nutrients. Amplexidiscus fenestrafer (above) attains a 4 in (10 cm) long. It needs
mass—hence its ghoulish common name. The diameter of at least 12 in (30 cm). well-lit conditions because
lobes contract if touched. a large part of its food is
supplied by symbiotic
photosynthetic algae.

ANEMONIA ALICEMARTINAE
Described as a new species in
2001, this bright red anemone
is found on the rocky
coasts—including tidal
pools—of northern
Chile. Scientists
suggest that such
a conspicuous
species has not
been spotted
before because
its population
has only recently
expanded over
the last decades.

REEF SOFT CORALS HORMATHIID SEA ANEMONES
Like dead man’s fingers, Sarcophyton species These widespread sea anemones commonly form
belong to the order Alcyonacea, and have the symbiotic relationships with other marine invertebrates,
same fleshy texture. Members of this genus living on mollusk shells or the carapaces and even
are most common in warm parts of the Indian claws of crabs. The anemone gains food scraps,
and Pacific oceans, and form colonies up to while its partner is protected by the anemone’s
31⁄4 ft (1 m) across. stinging tentacles. The species above, Stylobates
aenus, grows up to 8 in (20 cm) tall.

CNIDARIANS 539

PORITES SP. antlerlike MUSHROOM CORALS PAVONA SP.
These massive corals, found in tropical waters, are second growth While most corals are colonial, mushroom corals This species in the genus Pavona has a
only to the staghorns as reef builders. They grow in the consist of a single polyp usually less than 20in diameter of 10 in (25 cm) and is a common
form of mounds, sometimes with large, blunt, fingerlike (50cm) across. They live in tropical waters and, and conspicuous member of reefs from the Red
projections. Some Porites domes on the Great Barrier when young, are attached to the seabed by a stalk. Sea to the eastern Pacific. It has fine, starlike
Reef are almost 33 ft (10 m) in diameter, and may be When adult, as in the Fungia species above, they markings on the surface, and grows in spreading
200 years old. The individual polyps, however, are break away from the stalk and rest on the bottom. colonies that form columns, plates, or fronds.
only about 1⁄8 in (3 mm) across.
STAGHORN CORALS
large The staghorns, belonging to the genus Acropora, are among the fastest growing
polyps
corals on reefs. They would quickly swamp most other species if not for the fact
that they are fragile and easily damaged in storms. Found in tropical seas,
many staghorn colonies resemble antlers or bushes—like the branching
species on the left, which may be 61⁄2 ft (2m) tall. Some are more
spreading and resemble the flat-topped acacia trees on the East
African savanna. The platelike growth of the species below—
up to 93⁄4 ft (3m) across—intercepts light for its symbiotic
algae and shades out potential competitors beneath.

platelike I N V E R T E B R AT E S
shape

BRAIN CORALS
The individual polyps of this Lobophyllia colony are relatively large—
11⁄4 in (3 cm) in diameter or more. They are arranged in meandering
rows, giving the coral a brainlike form. Mature colonies of brain coral
may weigh over a ton. Many species inhabit the Pacific Ocean.

Class Scyphozoa translucent, LION’S MANE JELLYFISH
domed bell With a bell that can be over
Jellyfish 61⁄2 ft (2 m) across, the lion’s
mane jellyfish, Cyanea
Occurrence 234 spp. worldwide; in marine plankton, capillata, which lives in
a few on seaweed or the seabed northern waters, is one
of the biggest in the world.
With bodies that can be over 61⁄2 ft (2 m) Its numerous long tentacles
across and tentacles that may extend pose a danger to swimmers,
many yards, jellyfish are among the
largest animals found in plankton. and even when stranded on a
A few species, however, attach beach, this jellyfish retains its
themselves to seaweeds, and some ability to sting for a long time.
spend much of their time on the seabed.
A jellyfish’s body, or “bell,” is shaped like outer and inner cell layers (see p.537). MARIVAGIA STELLATA MASTIGIAS PAPUA
an inverted saucer or bowl, and consists The mouth in the center of the underside Discovered in the Mediterranean in 2010, this These broad-bodied jellyfish, some up to 7 in
mainly of a thick layer of jellylike opens into a simple gut, and stinging species belongs to a group of jellyfish called (19 cm) across, are most common in the tropics.
mesoglea sandwiched between the tentacles hang down from the bell rhizostomes—characterized by having a complex They are rhizostomes and—like Marivagia stellata
margin. These simple animals can have system of tiny mouths opening along specialized (left)—lack the margin of tentacles found around
CASSIOPEA complex life cycles. Some (but not all) frilly “arms” that hang beneath the bell. the bell of many other jellyfish.
XAMACHANA begin life as small polyps on the seabed.
A roughly disk-shaped jellyfish, 12 in (30 cm) These split into a stack of tiny medusae,
across, this species lives in warm, shallow or baby jellyfish, which drift away to
waters, and usually lies quietly pulsating upside start life on their own, growing into
down on the seabed. For nutrition, it relies on sexually reproducing adults. Although
the symbiotic photosynthetic algae that fill the jellyfish can swim by contracting their
bladderlike structures around its mouth. muscles, they make little headway
against even a gentle current, and
are often washed up on beaches after
storms. Most are carnivorous, catching
prey with their tentacles. This class
includes species such as the moon jelly
and lion’s mane jellyfish.

540 CNIDARIANS

Class Hydrozoa polyps, with different polyps being PORTUGUESE MAN-OF-WAR
shaped for different tasks. The result is a Found almost worldwide in
Hydrozoans colony that looks and works like a single tropical and temperate seas,
animal. Planktonic colonies may also the Portuguese man-of-war,
Occurrence probably 3,800 spp. worldwide; in have polymorphic polyps, with some Physalia physalis (right), has
plankton, and on sea, river, and lake beds catching prey and others digesting the a well-deserved reputation
catch. Mostly carnivorous, hydrozoans for being dangerous. It looks
This group of cnidarians contains a use their tentacles to capture organisms like a single animal, but it is
diverse array of animals, with various ranging from minute planktonic animals actually a highly integrated
body shapes and lifestyles, and sizes to sizable fishes; some are dependent colony of polyps, some of
ranging from as small as 1⁄32 in (1 mm) on symbiotic photosynthetic algae. Most which pack a powerful sting.
to as large as 31⁄4 ft (1 m) across. In the animals in this class—which includes A large, gas-filled float keeps
course of their lives, they usually pass the sea fir and by-the-wind-sailor, as the colony at the surface, and
through both an attached polyp stage well as the freshwater hydras—are supports trailing tentacles
and a free-living medusa stage. Most harmless to humans, but a few, including up to 66 ft (20 m) long. These
are colonial, containing tens to the notorious Portuguese man-of-war, tentacles contain polyps that
thousands of polyps. Some colonies have potentially deadly stings. They are catch prey, ones that digest
have hard skeletons and resemble preyed on by some mollusks, food, and others that enable
corals, while others are often mistaken gastropods, polychaetes, sea the colony to reproduce.
for jellyfish, drifting through the surface spiders, starfish, and fishes.
waters. Colonial forms that remain on Reproduction occurs both
the seabed mostly have polymorphic sexually and asexually.

sail

I N V E R T E B R AT E S BY-THE- float POLYORCHIS SP.
WIND-SAILOR retractable This delicate hydrozoan medusa has a
The coin-shaped Velella tentacles transparent bell up to 11⁄2 in (4 cm) across,
velella—4 in (10 cm) in with about 90 tentacles trailing from it.
diameter—is a highly modified hydroid polyp Common on the west coast of North
that, like the Portuguese man-of-war, drifts on America, it feeds on planktonic animals.
the ocean surface. It is moved by the wind acting FEATHER HYDROIDS
on the small sail attached to the float and, after Species in the widespread genus
storms, is often washed up on tropical shores. Aglaophenia live in shallow water, and their
dead remains are often washed up by the
tide. Each colony can be up to 231⁄2 in
(60 cm) high, and contains numerous
feeding and stinging polyps, as well as
larger reproductive polyps—the solid
yellow structures in the picture (right)—
which release floating larvae into the water.

HYDRA SPP. flask-shaped polyps with
Often used as a textbook example of a hydroid, the 2 rows of tentacles
genus Hydra is, in fact, unusual because its members
HYDRACTINIA SPP. are solitary, not colonial, and are not surrounded by a
Members of the genus Hydractinia, distributed calyx—a secreted tube. These tiny animals, 1 in (2.5 cm)
worldwide, are small, colonial hydroids, typically high at most, live attached to stones, submerged wood, or
3⁄4 in ( 2 cm) high, that often form encrustations plants, in bodies of freshwater
on animals. The hydroids get improved access to throughout the world. A large
food by being carried around, and in return, protect number contain photosynthetic
their host with their stings. Hydractinia echinata algae, which give them a green color.
grows on shells of hermit crabs (see above).
branching DISTICHOPORA VIOLACEA polyp’s stomach
growth form A few hydrozoans resemble corals and have extends down stem
a hard exoskeleton that protects the polyps. TUBULARIA SP.
Found in shallow waters
Most of these are quite small around the world, Tubularia
and brightly colored, such species look remarkably
as the Indo-Pacific species like plants. Their
Distichophora violacea (left), colonies grow from
which is 2 in (5 cm) high. “roots” that cling to rocks
and wrecks, and consist of
A few, such as fire “coral” a dense tangle of branching
Millepora, grow into very “stems,” with a polyp at each
large colonies. tip. Most colonies are less
than 6 in (15 cm) high.

FLATWORMS 541

Flatworms

PHYLUM Platyhelminthes Flatworms are the simplest of connective gut
CLASSES 6 all the animals that have bilateral tissue dorsoventral
ORDERS 41 symmetry. Their bodies are solid longitudinal muscle
FAMILIES 424 rather than containing an internal muscle
cavity, and they have no blood or
gut
SPECIES About 30,000 circulatory systems, and no organs branch

for exchanging gases with the

environment. Flatworms include many parasites, such BODY SECTION FREE-LIVING FLATWORMS

as tapeworms and flukes, as well as a variety of free- Flatworms have a simple body that is Since flatworms rely on diffusion to take in oxygen,
not divided into segments. The space their bodies have to be thin. This requirement makes
living forms that are abundant in freshwater habitats between the internal organs is filled large species—such as this marine turbellarian—much
with spongy connective tissue. more fragile than other animals of a comparable size.
and in the sea, particularly on rocky coasts and reefs.

Class Turbellaria less than 1⁄32 in (1 mm) to 20 in (50 cm) Class Cestoda TAENIA TAPEWORMS I N V E R T E B R AT E S
long. The largest species are paper The widespread Taenia
Turbellarians thin, and this helps them absorb Tapeworms species—some over
oxygen directly from their surroundings. 33ft (10m) long—live
Occurrence c.5,400 spp. worldwide; on rock and Unlike other flatworms, which are Occurrence c.4,000 spp. worldwide; within other in humans and other
sediment surfaces in water, in damp soil, under logs parasitic, most turbellarians are free animals, mostly cartilaginous fishes mammals. An adult
living and have simple sense organs to specimen is shown
Turbellarian flatworms show a variety help them negotiate their way around Highly specialized for their parasitic way above, while the suckers
of different shapes. Although they their habitat. Many of them move by of life, tapeworms are usually less than close-up on the right on scolex
have a distinct front end, the mouth creeping, but some of the bigger 1⁄32 in (1 mm) thick, but can be up to 100 ft
is positioned some way back on species swim by rippling their bodies. (30 m) long. As adults, they live in the
the underside of the body. Most The majority of turbellarians are intestines of vertebrates—including
turbellarians are translucent, black, predators, feeding on other small humans—and they absorb food directly
or gray, but some marine species— invertebrates; some are parasitic, some through their body wall. Tapeworms grow
particularly ones that live in coral are commensal, and a few depend on from a region just behind the head,
reefs—have brightly colored forming a long line of segments called
markings. They may be symbiotic photosynthetic algae. proglottids, each of which houses a
Almost all are hermaphrodites. complete reproductive system. As the
black and proglottids age, they break away from
yellow bands MARINE FLATWORMS the “tail” and leave the host in the feces,
Some marine turbellarians are large carrying eggs with them. If eaten by
and brightly colored. This species— an appropriate host animal, the eggs shows the head, or scolex. It is equipped with
Psuedoceros dimidiatus—is common develop—and the cycle begins again. hooks and suckers, with which the worm fastens
on coral reefs in the Indian and Pacific itself to its host’s intestines.
oceans, and grows to 2 in (5 cm) long. Class Trematoda
It shows a variety of color schemes,
Flukes
including black and yellow traverse
bands and a line of black blotches. Occurrence 18,000 spp. worldwide; within or on
other animals
diseases, including bilharzia, which
affects millions of people
in the tropics.

broad head TERRESTRIAL FLATWORMS Like tapeworms, flukes are wholly LIVER FLUKES
with many Land-dwelling turbellarians often have elongated parasitic, but they have a quite different Several species
eyes bodies, with head flaps bearing numerous small shape. They are typically cylindrical or of flukes live in
eyes. The Bipalium species, shown here, is one leaflike, with hooks or suckers at one the livers and bile
of the largest terrestrial forms, sometimes or both ends, or on the underside. Their ducts of mammals, including
reaching 14 in (35 cm). Originally from the tropics, length ranges from less than 3⁄8 in (1 cm) humans, causing severe damage and
it has been introduced throughout the world via to, in exceptional cases, as even death. The species shown above is the
potted plants, and is now a widespread pest. much as 20 ft (6 m). Unlike widespread sheep liver fluke, Fasciola hepatica,
tapeworms, flukes have which grows to about 11⁄4 in (3cm) long. Its
mouths and digestive intermediate hosts are freshwater snails.
systems, and they often
paper-thin burrow through their hosts’ BLOOD FLUKES slender
body tissues. While some attach Blood flukes are estimated female
themselves to internal organs,
others are external parasites. Their life to infect over 200 million
cycles are remarkably complex, involving people, besides occurring
BROWN FRESHWATER FLATWORM a variety of larval stages, and up to 4 in other mammals
Many turbellarians found in freshwater different hosts. The intermediate hosts and in birds, causing
streams and ponds are drab in color, but are often mollusks, but the final host— schistosomiasis or bilharzia;
their simple eyes—pigmented cups with which harbors the adult stage—is usually larvae attempting to bore through
light-sensitive retina but no lens—are often a vertebrate. Flukes can cause serious human skin also cause “swimmer’s
clearly visible. Dugesia tigrina is native itch.” Unusually, the sexes are separate, although
to North America, but introduced into Europe. the male lives wrapped around the female. This
Like other turbellarians, they have a single branching gut often tropical species, Schistosoma mansoni, is 3⁄8 –1⁄2 in
opening to the gut and move by gliding along visible through (1–1.5cm) long.
on a layer of microscopic hairs called cilia. body wall

542 SEGMENTED WORMS

Segmented worms EARTHWORM BURROWS

PHYLUM Annelida The bodies of segmented worms—or annelids—differ from Feeding mainly on decaying vegetable matter, earthworms are present in soils
CLASSES 4 other worms in being divided into a series of linked but partly throughout the world. They are usually found close to the surface but rarely
ORDERS 17 independent sections, each segment containing the same leave their burrows, to avoid being eaten by birds and other animals.
set of organs. The segments are filled with fluid
FAMILIES 130
which, combined with the musculature,

SPECIES About 18,000 gives the body its shape. Segmented

worms have various modes of life,

many are burrowers, living either in soil or in sediments

beneath freshwater or the seawater.

Anatomy body longitudinal
cavity muscle
A segmented worm’s body consists of a head
at one end, a tail at the other, and many trunk gut
segments in between. Each segment is divided
from the others by partitions and contains circular muscle chaetae Movement
distinctive organs. The mouth is on the first
segment, and leads to the gut which passes An earthworm moves by
through all the segments to end in an anus in coordinating the action of
the tail. On the side of each segment are hooks muscles in different parts of its body.
and bristles (chaetae). Some marine worms In each segment, there is one layer
have sensory tentacles; others, such as the of longitudinal muscle and another
earthworms, have no obvious projections. of circular muscle. When contracted,
these muscles make the segment
I N V E R T E B R AT E S FRESHWATER BODY SECTION either long and thin or short and WAVE MOVEMENT
PARASITES fat. As the worm moves through
The body cavity of an its burrow, short, fat segments When an earthworm moves, its
Leeches are parasitic earthworm is filled with anchor part of the body against segments alternately narrow and widen,
worms. They use 2 fluid and contains a large the wall, while long, thin segments forming waves of muscular contractions
suckers, one at each gut. Short chaetae project penetrate farther through the soil. that pass along the body.
end of the body, to attach through 2 layers of muscle
themselves to their hosts. to the body’s outer surface.

Class Polychaeta members of this class. Despite being or suspension feeders, and have very SEA MOUSE
abundant and sometimes brilliantly specialized parapodia. A few species are Somewhat inappropriately named after the
Bristleworms colored, bristleworms often escape parasitic. Most bristleworms are solitary Greek goddess of love, Aphrodita aculeata
attention because of their burrowing animals, but some tubeworms
Occurrence 12,220 spp. worldwide; in burrows and or tube-dwelling lifestyles and their may form large colonies or has a feltlike mass of chaetae
tubes, in coral reefs, and amid seaweed and animal quick reactions when disturbed. The reefs. The sexes are covering its dorsal surface
colonies on the seabed exceptions to this rule are the active usually separate. and scales. This marine
hunters, such as ragworms, which can scaleworm is up to 8 in
Bristleworms, also called polychaetes, sometimes be spotted in rock pools or eyes (20 cm) long, and is
form the biggest and most varied class under stones. Most bristleworms are widespread.
of segmented worms, ranging from less long, slender, and worm shaped, but coarse chaetae on sides feltlike
than 1⁄32 in (1 mm) to 93⁄4 ft (3 m) long. some may be almost circular. They dorsal chaetae
Lugworms, bloodworms and ragworms, have parapodia—flaps bearing bristles, RAGWORMS
tubeworms, and bamboo worms are all or chaetae—or at least ridges projecting Many marine polychaetes, like eyes
from the sides of each segment, and the ragworm, live in burrows
feeding tentacles heads that bear appendages. Two in soft sediment, but can chaetae
extending from tube general types occur: free living and swim well and actively
often carnivorous species, which have pursue their prey. The
tube made well-developed parapodia along the predatory lifestyle of the
by worm body; and sedentary species, which Atlantic species Alitta virens
dwell in burrows or tubes, are deposit (right)—which may be up to
20in (50cm) long—is reflected
tentacles fanned paddlelike in the numerous sensory structures,
to capture food appendages including eyes and large jaws, at its head end.

FANWORMS PARCHMENT WORMS
Some polychaetes live within Some marine polychaetes live in a U-shaped hidden within sediment. They draw
a tube of their own making, in a current of water by beating paddlelike appendages; potential food particles
which may be attached to are filtered from the current by a bag of mucus threads. Seen here out of its
a hard surface or, as in this
fanworm, partially buried in tube, the parchment worm, Chaetopterus variopedatus, is large, up to
soft sediment. Their movement 10 in (25 cm) long, but fragile.
is largely restricted to within
the tube, but their feeding

tentacles extend out into the water.
The widely distributed species shown here—
Sabella pavonina—is 8 in (20 cm) long.

ROUNDWORMS 543

Class Clitellata earthworm and its relatives. small sucker narrow segments MEDICINAL LEECH
Earthworms belong to the on head Most leeches capable of penetrating human skin
Clitellates biggest subgroup, the oligochaetes live in tropical rain forests, but Hirudo medicinalis
(comprising about 5,000 species), EARTHWORMS
Occurrence c.8,000 spp. worldwide; in soil, freshwater which live mainly in soil, silt, and Found almost worldwide, these familiar (left) lives in temperate freshwater, and
or marine sediments, on marine fishes freshwater. Leeches form a smaller grows to over 43⁄4 in (12 cm) long. It was
group (about 500 species), and are invertebrates are often seen when they once commonly used by the medical
Habitat All except dry regions either predatory or parasitic. Unlike emerge from their burrows in damp profession as a bloodletting agent. When
polychaetes, clitellates lack parapodia conditions, or are pulled from safety by it bites, a leech may inject both
Clitellates are characterized by the and head appendages, and are birds. As Charles Darwin pointed out, their
presence of the “clitellum,” a largely hermaphrodites. They may importance in aerating and enriching soil is anticoagulants and anesthetics.
dorsal area of glandular skin that be up to 93⁄4 ft (3 m) long. enormous. Lumbricus terrestris (left) can
secretes a cocoon where fertilized attain a length of 14 in (35 cm). large sucker
eggs are placed. The eggs clitellum on tail
hatch into miniature versions HORSE LEECH
of the adults—an adaptation Leeches that feed
to life on land where aquatic- on mammals and
style larvae cannot survive. This fishes are ectoparasites
class contains some of the world’s whose hosts survive the attacks. The horse leech,
most familiar invertebrates—the common Haemopsis sanguisuga (above), found throughout
Europe, Asia, and North America, can measure
21⁄4 in (6cm) long when at rest.

Roundworms Class Secernentea

Secernenteans

PHYLUM Nematoda Also known as nematodes, these Occurrence 14,000 spp. worldwide; in water- mouthparts I N V E R T E B R AT E S
CLASSES 2 worms are among the most abundant of all filled areas around vegetation and in soil, on plants, with piercing
ORDERS 17 animals. Roundworms are either free living or in animals style
FAMILIES 160 parasitic. The parasitic forms, which include
hookworms, pinworms, and threadworms, The physical differences between hard
secernenteans and other roundworms, outer
SPECIES About 26,000 live inside almost all types of plants and such as adenophoreans (see below), cuticle
are very technical, relating, for
animals, and some are a significant cause example, to types of sense organs. ASCARIS
Secernenteans are mostly parasites, LUMBRICOIDES
of disease. Free-living roundworms are also widespread in some causing serious diseases. They About a sixth of the
vary greatly in size, from microscopic to world’s population suffers
all aquatic habitats, including small films of water on land. several yards long. The largest known from ascariasis, an infection
secernentean, up to 30 ft (9 m) in length, by this parasitic roundworm, which can grow
Their bodies are unsegmented, round in cross section, and lives in the placentas of female sperm up to 16 in (40 cm) long. The infection starts
whales and is believed to be the largest when the eggs are inadvertently taken into the
tapered toward each end. They have a complex cuticle that member of the roundworm phylum. gut with food. The larvae migrate to the lungs,
However, the harmful effect of these returning to the gut as adults.
is replaced 4 times by molting, parasites is not necessarily related to
their size: microscopic roundworms,
between hatching from such as pinworms, filarial worms, and
hookworms, can multiply rapidly in
an egg and reaching the host, causing great damage (as
in elephantiasis).
sexual maturity.
WUCHERERIA BANCROFTI
sensory tentacles This microscopic roundworm is the cause of
around mouth elephantiasis in humans, a tropical disease that
produces disabling enlargement of soft tissues,
MOVEMENT particularly in the legs. The worm lives in the
Roundworms are lymphatic system, and is spread by mosquitoes.
unusual in having
longitudinal but Class Adenophorea
not circular
muscles. They move Adenophoreans
by thrashing their
bodies in a single plane, Occurrence c.12,000 spp. worldwide; in water-filled
in the process forming areas around vegetation and in soils, on plants, animals
characteristic C- or S-shapes.

nerve cord gut
cuticle
tubelike, Habitat All except desert regions
excretory unsegmented body TRICHINA WORM
canal Adenophorean roundworms are Trichinella spiralis is a small roundworm,
body cavity BODY SECTION mainly free living rather than parasitic, 1⁄32 in (1mm) long, which lives mainly in rats and
The large central cavity in a roundworm’s and are commonly found in most other small mammals. Pigs may pick it up while
longitudinal muscle body is occupied by fluid-filled cells. The high kinds of habitat throughout the world, scavenging and, by eating undercooked pork,
internal pressure in this cavity, together with a particularly in marine sediments. each year about 40 million humans do the same.
lattice of fibers in the cuticle, prevents the body They range in size from microscopic
from shortening when the muscles contract. to as long as 31⁄4 ft (1 m) in exceptional
cases. Surveys of seabed mud
suggest that vastly more may be
awaiting discovery.

544 MINOR PHYLA

Minor phyla MICRO-ANIMALS
Rotifers occur in large numbers in all
The invertebrate world is classified into about 30 head kinds of watery habitats. They are so small
major groups, or phyla. Some contain common and that they are dwarfed by some forms of
familiar animals but well over half contain organisms trunk
that go largely unnoticed—because they are rare, bacteria—a characteristic that is shared
because they are microscopic, or because they live by animals in several other minor
in inaccessible habitats, such as seabed mud. These phyla. Zoologists call these tiny
animals differ from each other as much as invertebrates animals micrometazoans.
differ from vertebrates, and they have widely divergent
ways of life. Some minor phyla, such as arrow worms, digestive system
comprise just a handful of species, while a few—such
as bryozoans—contain thousands of species, yet both tail
groups are ecologically important. A selection of minor
phyla is shown on these 2 pages.

Phylum Ctenophora Phylum Sipuncula Phylum Bryozoa form colonies. Some bryozoans
grow as encrustations on rocks
Comb jellies Peanut worms Bryozoans and seaweeds, but others develop
a branching, plantlike shape and
Occurrence c.200 spp. worldwide; planktonic, a few on Occurrence c.150 spp. worldwide; in soft sediments, Occurrence c.6,000 spp. worldwide; attached to hard wave backward and forward in the
the seabed mollusk shells, rock crevices, holes in coral or wood surfaces or aquatic environments water. Once dead, these branching
colonies are often washed up on the
I N V E R T E B R AT E S With their tentacles extended, comb These plump, unsegmented worms, Also called sea mats, ectoprocts, or shore, where they may be mistaken
jellies, or sea gooseberries, are some polyzoans, bryozoans are tiny aquatic for dried-out seaweed. This phylum is
of the most attractive and graceful 1⁄16 – 28 in (0.2 – 70 cm) long, have a animals, less than 1⁄32 in (1 mm) long, ecologically important as a source of
animals in the sea. Although they can which live inside boxlike cases that food for some marine invertebrates.
swim, by beating their comblike plates peanut- or sausage-shaped body, are joined together to
of fine cilia (structures similar to hairs), is pushed out by hydraulic pressure in
they make little headway against the with walls formed of layers of circular and order to catch prey; in one large group
current, and are often carried along in of species, it bears piercing barbs that
large swarms by the tide or the wind. longitudinal muscles. Their most notable allow it to inject toxins. These worms
As the cilia rows beat, they produce range from less than 1⁄64 in (0.5 mm) in
beautiful, iridescent colors. Most comb feature is their retractable trunk, known length to over 165 ft (50 m). All have a
jellies are small in size, but circulatory system and most have
some can grow to as an introvert, which is extended with moundlike eyes—up to 250 in some species. Many
61⁄2 ft (2 m) long. are brightly colored. Two groups of these
the help stout ROSS CORAL shape worms are commensal—one within the
SEA GOOSEBERRY body shells of bivalve mollusks, the other on
Comb jellies come in a of hydraulic Bryozoans bud and within the shell of a variety of crabs.
variety of shapes, from pressure, and continuously until thousands
spheres to ribbons and UNIDENTIFIED SP.
disks. The Atlantic-dwelling retracted by of interconnected “zooids” Ribbon worms are
Pleurobrachia pileus (right) noted for their flat
is 3⁄4 in (2 cm) long and muscles. Peanut are produced. The North and sometimes
has a pair of tentacles extraordinarily long
6 in (15 cm) long. worms are suspension or Atlantic Pentapora fascialis bodies. The worm
shown here belongs
deposit feeders, and collect may form colonies up to to a group that includes
the world’s longest
organic particles by means of a 61⁄2 ft (2 m) in diameter. animal, which reaches
a length of 180 ft (55 m).
ring of hydraulic tentacles around This is twice as long
as the average adult
the mouth. They appear to be blue whale.

most closely related to mollusks. Phylum Nemertea

GOLFINGIA VULGARIS Ribbon worms
This species of peanut worm,
found on northwest Atlantic Occurrence c.1,400 spp. worldwide; on bed and in
coasts, lives in mud below the surface or middle waters of seas, rivers, and lakes,
low-tide mark. It is 4 in (10 cm) long. in forests

Phylum Rotifera crown of A key feature of these mainly marine
tiny hairs worms is their unique proboscis. This
Rotifers muscular tube, housed above the gut,

Occurrence c.2,000 spp. worldwide; in vegetation
in lakes, rivers, and seas, microfreshwater habitats
on land

Rotifers are among the smallest animals: UNIDENTIFIED SP.
the largest is just 1⁄8 in (3 mm) long. They Although some rotifers are marine, most live in
live in water, and are either free- freshwater habitats, including temporary pools
swimming, or attached to solid surfaces. such as those in gutters and water films around
The trumpet-shaped to spherical body leaves and soil particles. Like water bears (see
usually has a “wheel organ” in front, opposite), they are specially adapted to survive
formed by 2 whorls of hairlike structures drought. They can exist in a dried-out state for
(cilia), which is used for feeding and many years, coming back to life as soon as
locomotion. Many are transparent, they are rehydrated.
and several are parthenogenetic,
males among these being unknown.

MINOR PHYLA 545

Phylum Brachiopoda stalks attached, but the 2 groups are Phylum Phoronida PHORONIS SP. I N V E R T E B R AT E S
not related. Also known as lamp shells, Members of the widespread genus Phoronis
Brachiopods brachiopods are especially abundant Horseshoe worms can be 10 in (25 cm) long, but most are
in colder waters. They are less than 4 in much smaller. They have an unsegmented
Occurrence c.400 spp. worldwide; attached to hard (10 cm) long, and most of the space in Occurrence c.20 spp. worldwide; in soft sediments body, usually encased in a chitinous tube
surfaces or buried in soft sediments on the seabed the shell is taken up by a loop or spiral or attached to hard surfaces on the seabed buried in sand or mud. The body wall has
of hollow, fringed tentacles (lophophore) layers of longitudinal and circular muscles,
Encased in bivalved shells, usually with surrounding the mouth, with which the These sedentary marine worms are which enable the worm to move up the
a stalk (pedicle) that may anchor the animal suspension feeds. Brachiopods generally less than 8 in (20 cm) long, and tube to feed, and to retreat afterward.
animal to a hard surface or be used are extremely common as fossils: usually remain encased in a secreted
in burrowing, brachiopods look some rocks are made up entirely of chitinous tube, with a horseshoe-shaped jaws similar in form to the claws on the
remarkably like bivalve mollusks with brachiopod shells. Once an important crown of as many as 15,000 feeding legs. These carnivorous animals catch
small group comprising more than 25,000 tentacles around the mouth. The sexes their prey by spraying them with a
tentacles species, brachiopods appear to have are separate in some species, while mucuslike substance from a pair of
declined as a result of competition others are hermaphrodite. Horseshoe slime glands opening on either side
Phylum Chaetognatha with bivalve mollusks. worms are most closely related to of the mouth; they use the same
brachiopods, or lamp shells (see left). technique to defend themselves
Arrow worms LIOTHYRELLA UVA from their predators.
Although brachiopods resemble Phylum Onychophora
Occurrence c.150 spp. worldwide; in plankton, one bivalves, the 2 halves of the MACROPERIPATUS TORQUATUS
genus on the seabed shell are dorsal (upper) and Velvet worms Velvet worms, such as Macroperipatus torquatus
ventral (lower), not left and (below), inhabit warm and humid regions. Their
right. The species featured, Occurrence c.180 spp. in tropical and southern anatomy is basically that of a worm but, like
temperate zones; in moist forests, leaf litter, under arthropods, they have pairs of legs serially
Liothyrella uva, is common stones repeated along the body. The legs are fleshy,
in Atlantic waters, and unjointed, and hydraulically operated.
has a shell that is up These are the only survivors of a group
to 3⁄4 in (2 cm) long. of worms that were abundant in the
Cambrian Period. They have cylindrical,
Phylum Tardigrada wormlike bodies, up to 6 in (15 cm) long,
14 – 43 pairs of short, unjointed, fleshy
Water bears legs, each terminating in a pair of claws,
and an antennae-bearing head with
Occurrence c.1,000 spp. worldwide; in freshwater, salt
water, and damp and wet terrestrial habitats

Habitat All except dry ones

Growing only up to 43⁄4 in (12 cm) long, Water bears—or tardigrades—are
arrow worms are relatively small, highly plump-bodied, microscopic animals
active predators that can eat a third with 4 pairs of stubby, clawed legs.
of their own body weight a day. They Their lumbering movements are
catch their prey—animal plankton, remarkably bearlike, but their closest
including larval fishes—with movable relatives are probably velvet worms.
spines around their mouths and kill They live in damp habitats such as
it by injecting tetrodotoxin, a potent moss, but can shrivel into a dry husk
poison produced by symbiotic bacteria, during drought and survive this way for
and used by very few animals. years. Water bears lay eggs, but some
females are parthenogenetic.

SAGITTID SP. UNIDENTIFIED SP. Phylum Hemichordata that may be prehensile or connect
The small, torpedo-shaped, transparent arrow Water bears inhabit water films on land and individuals to form colonies; and free
worms are carnivores. Like the Sagittid species live between sand grains and crevices on the Hemichordates living, wormlike forms, in which the
above, they live among the plankton in all the seabed. Many live in clumps of moss on roofs trunk is stalkless and bears a terminal
oceans—where their large numbers can have and in gutters. By being dormant for extended Occurrence c.130 spp. worldwide; in marine mud and anus. The sexes are separate, and
great ecological impact; for instance, on fish larvae. periods, they may live over 50 years. sand, and other intertidal and subtidal habitats reproduction occurs either sexually
or asexually, by fragmentation
Phylum Echiura with bulbous, sausagelike bodies. Hemichordates are unusual among or budding.
Females are up to 20 in (50 cm) long, invertebrates in that they have some
Spoonworms with an even longer proboscis for vertebrate characteristics: a nerve wormlike
sweeping up food. Males are minute cord that runs along the back, and body
Occurrence c.200 spp. worldwide; in burrows and live parasitically inside their partners. pharyngeal perforations—structures
or other cavities on the seabed that have the same anatomical origin ACORN WORMS
BONELLIA VIRIDIS as fish gills. The length of the 3-part Slow-moving and fragile, acorn worms live
Spoonworms, or This European species has bodies—comprising a proboscis, a in U-shaped burrows in intertidal and subtidal
echiurans, are collar, and a long trunk—ranges from habitats in all parts of the world. The large trunk
sedentary, green, toxic skin. Females less than 1⁄2 in (1.2 cm) to 81⁄4 ft (2.5 m). of Balanoglossus australiensis (above), which may
marine animals are up to 6in (15cm) long, These animals are found in 2 forms: be 31⁄4 ft (1m) long, bears numerous gill slits.
with a proboscis that can sedentary, polyplike pterobranchs,
reach out for food over whose saclike trunk ends in a stalk
about 31⁄4 ft (1 m).

546 ARTHROPODS

Arthropods

PHYLUM Arthropoda Arthropods form the largest phylum of living organisms and MIGRATION
CLASSES 19 account for more than 3 out of 4 known species of animals.
ORDERS 123 They include insects, centipedes and millipedes (myriapods), Arthropods are among the most mobile of invertebrates.
FAMILIES About 2,300 crustaceans, and arachnids, among others. All arthropods Some species make use of this to migrate in response
to changes in environmental conditions and food supply.
SPECIES About 1.2 million have an exoskeleton that covers a body divided into Each year, many spiny lobsters make mass migrations
between relatively warm and cool waters. Typically
segments, and all have jointed legs. The first arthropods moving in single file, they maintain contact with one
another by touch (using their antennae) or sight (picking
CLASSIFICATION NOTE were marine animals, and many (especially crustaceans) out the light-colored spots on the abdomen of the
individual in front of them). The fall migration is
Arthropods are divided into 2 are still found in the sea. However, insects, arachnids, and often triggered by violent storms.
subphyla: chelicerates have myriapods have successfully adapted to life on land. Insects,
pincerlike appendages and no which are by far the most numerous of all arthropods, are
antennae, while mandibulates the only invertebrates capable of powered flight, having
have chewing mouthparts and evolved functional wings more than 100 million years
one or 2 pairs of antennae. before flying reptiles or birds. By providing food for
many larger animals, arthropods have become
MANDIBULATES essential to the functioning of most of the
Hexapods (insects and other world’s ecosystems. Krill, copepods, and
other crustaceans form the foundation
6-legged arthropods) see
pp.548 – 77
Centipedes and millipedes
see p.578
Crustaceans see pp.579 – 84

CHELICERATES
Sea-spiders see p.585
Horseshoe crabs see p.585
Arachnids see pp.586 – 93

of marine food chains, supporting

I N V E R T E B R AT E S fish and marine mammals. On land, insects provide

food for countless other animal species.

Anatomy

Arthropods share several common features.

All species have a bilaterally symmetrical

body that is divided into segments (see below).

Arising from these segments are several jointed legs,

which are arranged in pairs. The body is covered by a

tough exoskeleton, which is produced by the epidermis

and is composed of protein and a material called chitin.

To allow for movement, the exoskeleton articulates at joints

and hinges, where the cuticle is soft and flexible. In large

marine species, the exoskeleton is strengthened by calcium

carbonate, while land species have a thin layer of waterproof

wax to stop them from drying

out. All arthropods have an

antenna open circulatory system:

their organs are bathed in a fluid

called hemolymph, which is

head moved around the body by the
heart. Gas exchange is carried out
first
trunk by gills, organs known as book
segment lungs, or a system of tracheae. The
nervous system consists of a brain

that is connected via paired nerve BODY SEGMENTS toughened CUTICLE
outer part
cords to networks of nerve cells Each segment (seen in cross section, of cuticle The cuticle (seen in cross
below) is essentially a box, with a top cuticle section, left) protects the
in the thorax and abdomen. (tergum), bottom (sternum), and sides dermal body of an arthropod
(pleura). These outer surfaces are made gland from damage and repels
jointed SEGMENTATION from tough, relatively rigid plates (sclerites), pathogens. Although it is a
leg which are joined by soft cuticle to allow for epidermis composite of several layers,
The body of an arthropod is divided into movement. Muscles between the tergum the cuticle can be repaired:
segments. Arthropods probably evolved and sternum allow the segment to be heart a small wound is quickly
from marine worms that had unspecialized flattened in shape, while those linking sealed; more extensive
segments. Over time, eyes, antennae, and adjacent segments allow the body tergum damage can be repaired
appendages appeared, and some segments to flex sideways, curl up, or gut by the production of a new
were fused into functional units, of which telescope lengthwise. The cuticle at the next molt.
the most common is the head. Primitive nerve cord, digestive system, Some species can also
species, such as myriapods (a centipede and heart pass through regenerate lost limbs.
is shown here), have a head and trunk. most segments.
In arachnids, the head and thorax are fused pleuron

flexible to form a cephalothorax. Insects, the most muscle for muscle connecting nerve sternum muscle for changing
cuticle advanced arthropods, have a head moving leg segments cord shape of segment
between (made of 6 fused segments), a
segments thorax (that has 3 segments), and
an abdomen (with 11 segments).

ARTHROPODS 547

Movement point of attachment coxa
to body segment
One of the key features that separates arthropods ischium LEG MOVEMENT WALKING
from most other invertebrates is their jointed limbs. basis merus
Most arthropods are active animals—moving by FORWARD AND An arthropod’s limb, such Most insects, including this beetle, walk with
walking, swimming, or jumping—which enables BACKWARD carpus as the first walking leg of a what is known as a tripod gait. As each leg
them to look for food or mates, colonize new MOVEMENT propodus crab (left), consists of a set is lifted off the ground, the body is supported
habitats, and escape from predators or adverse MOVEMENT of hollow, rigid sections. These by one leg on the same side of the body and
local conditions. The number of legs varies from UP AND DOWN are joined by areas of flexible 2 legs on the opposite side.
3 pairs in insects to several hundred pairs in movement at each cuticle and moved by muscles
millipedes. Each leg usually ends in a claw of joint can occur in that connect the segments.
some kind that improves the arthropod’s grip on only one plane The ends of the segments are
the surface. Many species also have adaptations, shaped so that movement at
such as bristles or adhesive pads, for walking on dactylus each joint occurs in a different
smooth, vertical surfaces or on water. In some plane to movement at the
species, the joints between leg segments contain an adjacent joints. The result
elastic protein, called resilin. When compressed, this is a limb that can be moved
acts as a reserve of energy that can be released into almost any position.
when the animal is on the move. In addition to
movement, arthropods also use their legs to catch
prey, to mate, and to communicate.

Feeding I N V E R T E B R AT E S

Growth Arthropods eat a wide range of foods. Some eat decaying organic
matter (saprophagous), others eat the tissues of other animals and
One disadvantage of having an exoskeleton is that it plants. Many species are specialized feeders, the shape of their
limbs and mouthparts reflecting the food they eat. Strong claws
must periodically be replaced with a larger one as and jaws can tear and cut tough material, such as skin, cuticle,
and plant tissue, while needlelike mouthparts are used to suck up
the animal grows. Arthropods grow and develop in liquids, such as sap, blood, and nectar. Many aquatic crustaceans
have featherlike structures on their legs or
various ways. Crustaceans, myriapods, and arachnids around the mouth that act like strainers
to filter minute organisms
molt throughout their adult life. Larval crustaceans PARENTAL CARE or organic particles from
water. Most arthropods
look nothing like the adults. In crabs, for example, It is not unusual for adult insects, use saliva to lubricate
their food as it
the egg hatches into a planktonic zoea larva. centipedes, and arachnids to care for passes into the
digestive system.
This becomes a bottom-dwelling their eggs and young. Female spiders
PREDATORS
megalopa larva, which in turn wrap their eggs in silk and carry or Most arachnids eat other animals.
However, they can ingest only liquid
develops into the adult. Young guard them until they hatch. Scorpions food. Having subdued a cockroach,
this scorpion will release digestive
myriapods typically look like brood their eggs and carry their young enzymes over its body and then
consume the resulting liquid.
small adults and become longer on their back after they hatch.
PLANT EATERS
by adding trunk segments at Herbivorous arthropods can eat
large quantities of food. A swarm
each molt, although some young adult climbs up plant of locusts can consist of up to
centipedes hatch with the stem to leave water 50 billion individuals, theoretically
adult number of segments. discarded skin of nymph capable of consuming 100,000 tons
Young arachnids typically of food in a day.

look like small versions of

their parents. With the MOLTING

exception of bristletails When molting, an arthropod’s body is soft and unprotected.

and silverfish, insects An immature damselfly (known as a nymph) molts several times

stop molting underwater. When ready for the final molt, it crawls out of the water.

upon reaching Once exposed, it must shed its skeleton and take to the air in

sexual maturity. a couple of hours if it is to avoid being eaten by a predator.

548 ARTHROPODS NON-INSECT HEXAPODS

Insects In addition to insects, hexapods include 3 smaller
classes: springtails, proturans, and diplurans.
PHYLUM Arhropoda Insects are the most successful animals on earth. They They are collectively known as non-insect
SUBPHYLUM Mandibulata account for more species than any other class: over a million hexapods, and a selection are described in this
SUPERCLASS Hexapoda have so far been identified, but it is thought that the true section. All non-insect hexapods are without wings,
number may be between 5 and 10 million. Insects belong and many also lack eyes and antennae. Unlike
CLASS Insecta insects, their mouthparts are enclosed in a pouch
located on the underside of their head.
ORDERS 29 to a group of arthropods called hexapods, all of which
SPRINGTAILS
FAMILIES About 1,000 have 3 pairs of legs. Many insects also have wings, which Springtails are small
hexapods that occur in
SPECIES About 1.1 million makes them the only arthropods capable of powered flight. great numbers in soil
and leaf litter all over
Combined with their small size and ability to survive in dry the world, including the
Arctic and Antarctic.
environments, flight has enabled insects to colonize a vast range of habitats.

Most live on land or in the air, but they are also numerous in freshwater.

Without insects, many other forms of life would not exist: the majority

of flowering plants are largely dependent on them for pollination, and

they form the main component of the diet of many animals. During their

lifetime, many insects undergo complete metamorphosis, passing

through several physical stages before reaching adulthood.

Anatomy

The body of an insect is divided into 3 segments—the head, thorax,

and abdomen—each of which performs different functions. The head

I N V E R T E B R AT E S supports the mouthparts and much of the sensory apparatus, including

the compound eyes and antennae. The thorax, which bears the legs and

in many species the wings, is important in locomotion, while the abdomen

contains the organs for digestion, excretion, and reproduction. All adult

insects breathe air, which enters the body through openings (called

spiracles) on the sides of the abdomen

segmented tarsus and thorax. Immature stages of
antenna aquatic species often have
gills. The internal organs
tibia compound
head eye are bathed in a fluid called
hemolymph, which transports

prothorax nutrients and waste and is

pumped around by a tube-

femur shaped heart.

coxa mesothorax

hingwing

Population

forewing There are several reasons why insects have become
so successful. Being small, they are able to occupy
folded metathorax microhabitats that are inaccessible to other animals.
hindwing abdomen Given the right conditions, they are also able to breed
very rapidly, enabling them to respond quickly to increases
BODY SEGMENTS COMPOUND EYES in the availability of food. For example, a single pair of bruchid
Insects have 2 types of eyes: simple beetles have the theoretical potential to produce enough
The body of a jewel beetle, eyes (ocelli) and compound eyes. This offspring to occupy the entire volume of the earth within
like that of other insects, is protected by hornet’s ocelli are on top of its head. 432 days. In practice, this doesn’t happen because there are
a rigid exoskeleton. There is some flexibility The forward-facing compound eyes limits to the food supply and because of competition between
between segments—for example, the head can individuals of the same species and between different species.
be moved independently. The thorax and abdomen consist of hundreds of light-sensitive
are further subdivided: the thorax consists of units connected by nerves to the brain. SPECIES NUMBERS
the prothorax, mesothorax, and metathorax, High reproduction rates
while the abdomen has up to 11 segments. MOUTHPARTS have enabled insects
The mouthparts of insects have to evolve so rapidly that
spongelike biting jaws evolved into an amazing array of forms. they make up over half
organ Like most insects, ground beetles have of all animal species
jaws suited for cutting and chewing. alive today. Bugs (such
piercing Houseflies use a spongelike structure to as these firebugs) alone
tube absorb exposed liquid. Mosquitoes use account for 88,000
needlelike mouthparts to pierce the skin species. Insects are
HOUSEFLY GROUND BEETLE MOSQUITO of other animals. found on land, in
freshwater, and even
on the ocean surface.