NAUTILUS

CLASS Cephalopoda

ORDER Nautilida

GROUP 6: PRIMITIVE ANIMALS FAMILY Nautilidae

... GENUS "11IIIIIIII Nautilus

Nautiluses are ancient members of the class Cephalopoda, which includes the most highly evolved marine mollusks. These animals

have survived almost unchanged for about 550 million years.

KEY FACTS

SIZES

Shell diameter: 4-11 in.

Weight: 13 lb.

BREEDING

Sexual maturity: 6 months.

Mating season: Probably year­

round.

No. of eggs: Usually about 10.

Each is 1 ~-2 in. long.

LIFESTYLE

Habit: Social; living in groups.

Night-active predator.

Diet: A variety of crustaceans

and dead or living fish .

Lifespan: Unknown.

RELATED SPECIES

There are some 700 species in

the class Cephalopoda. The single

genus of living nautiluses is divided

into 6 species, including Nautilus

pompilius, N. scrobiculatus, and N.

macromphalus. They are descen­

dants of ammonites.

FEATURES O F NAUTILUSES

Range of nautiluses.

DISTRIBUTION

The various nautilus species are found in parts of the Indian

Ocean and the southwestern Pacific Ocean.

CONSERVATION

Nautiluses are hunted for their shells. Although these animals

were once numerous throughout their range, they are becom­

ing increasingly rare. As a result, captive breeding programs

have been set up.

Shell: A slim spiral consisting of several successive chambers, which are added as the nautilus ages. Faint growth rings appear on the outside.

Hood: A shield­like structure formed from

the shafts of 4 tentacles that

have fused together.

INTERNAL ORGANS

A nautilus's organs are in the outermost chamber of its shell. They in­clude two pairs each

Siphuncle

©MCMXCVI IMP BV/IMP INC. WILDLIFE FACT FILpM

of gills and kidneys. Gills

Eye: Simple and mini­mally effective, picking up only changes in light.

Stomach Kidney

Tentacles: Emerge from the shell at night when the nautilus feeds. Chem­

ical receptors on the tips allow the animal to "taste" the surrounding wa­

ter and locate prey on the seabed. They also stabilize the nautilus and

help draw food toward its mouth.

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Nautiluses, which are sometimes referred to as chamber

snails or pearly boats, are found in parts of the Indian

and Pacific oceans. There are several forms of these sea

creatures, but each one has a flat, many-chambered shell

that contains small amounts of liquid as well as a gaseous

mixture. By distributing the gases within its shell, the

animal is able to control the depth at which it lives.

~ HABITS Nautiluses mostly live at depths of 75 to 2,000 feet in the warm, coastal regions of the Indian and the southwestern Pacific oceans. Except in the cold sea­son, they rarely come to shore, but they may swim toward the surface during the night. They orient themselves by smell and touch rather than sight, so they live in deep water where there is almost no light.

Some naturalists believe that nautiluses may migrate, but the tales of their reaching South Af­rica, Madagascar, New Zealand, or Japan seem unfounded. The shell, however, can float for three weeks after the animal

dies, so it may drift outside the nautiluses' range.

Each nautilus adds successive chambers to its shell as it grows. When the animal outgrows a cavity, it seals it off with a hard wall. The chamber is then filled with gas-mainly nitrogen but also some argon and oxygen. A full-grown adult may have up to 29 sealed chambers. Using its siphuncle, a tube that runs through its body and links all the chambers, the animal can change the pressure inside its shell, enabling it to rise or sink.

Right: An adult nautilus may have as many as 90 tentacles to help it assess its surroundings.

~ BREEDING The mating of nautiluses has not been seen in the wild. Cap­tive breeding programs have recently been established, but there is still much to learn about the animal's lifecycle.

The female has one ovary, at the back of her body, and her eggs float in an amber-colored fluid in a transparent capsule. She also has a small sac under her mouth for receiving sperm.

Left: The mottled, fleshy hood of a nautilus is made up of the fused stems of four tentacles.

DID YOU KNOW? • The name nautilus comes from the Greek word for "sail­or./I The animal was given this name because it resembles Argonauta nodosa, an unusual octopus that was thought by the ancient Greeks to use its tentacles as sails. Argonauta is now called the paper nauti­lus, because of its thin shell.

The male has a penis as well as two secondary sex organs. One is under his mouth. The other, called the spadix, con­sists of modified tentacles and is used for mating.

In captivity the female lays eggs in December. She lays 10 large eggs in about two weeks. In the wild the young probably live in warm water first, before moving to colder, deeper areas.

Right: A nautilus spends the day resting in its shell, with its tenta­cles drawn inside for safety.

• Nautiluses have astonishing powers of recovery. An ani­mal's wounds can heal within hours, without any scars, and its tentacles can grow again if they are broken off. • Nautiluses are the only sur­viving direct descendants of ammonites, which thrived in oceans millions of years ago.

~ FOOD & FEEDING A nautilus eats crabs, spiny lob-sters, prawns, fish, and carrion (dead animal flesh). It locates its prey with chemical receptors at the tips of its tentacles and near its gills since it cannot rely on its large but relatively undeveloped eyes. Its eyes lack lenses and fill with seawater, so they distin­guish only general shapes.

Left: When it is searching for food, a nautilus does not rely on its eyes because they are poorly developed and probably can distinguish only very general shapes.

A nautilus hunts primarily at night, searching on the seabed for food. Although it ordinarily swims backward, exhaling wa­ter through its funnel, it swims slowly forward when it is feed­ing and samples the seabed with its tentacles.

The animal uses its powerful, beaklike jaw to chew its food. It bites off large pieces of flesh and then pulls them into its mouth with its bristly tongue. A nauti­lus can spend 30 hours digest­ing a meal. Itthen uses its four kidneys to process the wastes.

Left: Nautilus flesh is edible, but the animal's shell is more valuable to hunters.

COMMON BRITTLE STAR '"'--___________ ~G:;.:;.R.:..:::O;..,;;U;;..;;.P.....;6=_:. PRIMITIVE ANIMALS

PHYLUM Echinodermata

CLASS Ophiuroidea

GENUS &: SPECIES Ophiothrix fragi/is

The common brittle star is a spiny-shinned sea creature related to starfish. It feeds by combing the water with its five highly

flexible limbs and trapping tiny floating animals.

KEY FACTS

SIZES Length of limbs: Up to 4 in.

Width of disk: Up to 1 in.

BREEDING Breeding season: Mainly in sum­

mer, when the water is warm and

food is abundant. Other times if

conditions are right.

Reproductive method: Each sex

ejects eggs or sperm into water.

Larvae: Mobile, planktonic.

LIFESTYLE Habit: Lives in groups on the

seabed or among rocks below

low tide level.

Diet: Small, floating planktonic

organisms.

RELATED SPECIES There are about 1,600 species of

brittle star throughout the world.

They are related to starfish, sea

lilies, sea urchins, and sea cucum­

bers-ali known as echinoderms.

Range of the common brittle star.

DISTRIBUTION The common brittle star is widely distributed in the eastern

North Atlantic Ocean, North Sea, and Mediterranean Sea.

The other 1,600 species of brittle star can be found in oceans

throughout the world .

CONSERVATION Brittle stars have no commercial value and are not directly

threatened by people.

FEATURES OF THE COMMON BRITTLE STAR

Central body: Disk-shaped. It contains the animal 's internal organs. Five iden­tical segments radiate from the cen­ter. Outer covering is hardened with calcite crystals.

~""vr

skeleton consists of interlocking

plates that pro­vide flexibility. If

the brittle star is seized, the

plates separate to help it escape.

Tube feet: Fingerlike appendages covered with cilia (tiny hairs) and arranged in double rows along the limbs. They trap food floating in the cu rrents and transfer it to a

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OTHER BRITTLE STARS

Ophiopholis acuJeata. Usually red. Lives under rocks on the British coast.

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As its name implies, the common brittle star is easily

"broken. /I If one of its limbs is trapped under a tumbling

rock or seized by a predator like the seven-armed starfish,

the animal simply sheds the limb in an attempt to escape.

This adaptation is its main method of defense. Once the

brittle star is able to free itself, it simply grows a new

appendage to replace the one that it has lost.

~STRUCTURE The common brittle star is close­

ly related to starfish. Unlike most

animals, it does not have an ob­

vious head and tail. Instead, it

has a radial body structure, with

five identical segments radiating

from the animal's center.

The disk-shaped center sec­

tion contains the animal's main

internal organs and, on the un­

derside, its mouth. The skin of

the central disk is toughened

with calcite (calcium carbonate)

crystals that make it hard and

spiny. This outer covering is typ-

ical of brittle stars and related in­

vertebrates called echinoderms, which means "spiny-skinned."

The limbs of a brittle star are

very different from the fairly rig­

id, fleshy limbs of a starfish . The

brittle star's long, slender appen­

dages are flexible and armored

with spiny plates of calcite. The

plates interlock somewhat like

the links of a bicycle chain, so

the brittle star can coil them in­

to tight loops, slip them into

crevices, and use them to move

through the water.

~ BREEDING When there is plenty of food

and the water is warm enough,

female and male brittle stars

produce eggs and sperm and

then eject them into the water.

Chemical signals probably stim­

ulate the two sexes to do this at

the same time. Because brittle

stars gather in huge swarms,

some of the eggs are fertilized.

But many eggs and sperm cells

are swept away by currents

without making contact with

one another. They become

food for fish or even other brit­

tle stars.

Left: The interlocking plates on its limbs make a brittle star more flexi­ble than a starfish.

DID YOU KNOW? • Mostly spines and bones, a

brittle star makes a poor meal

for a predator. Yet it may be

attacked by its own relative,

the seven-armed starfish, or

by bottom-feeding cod.

• A brittle star has a simple

nervous system. It can sense

which way is up, smell food

The fertilized eggs develop

into tiny larvae that are quite

unlike their parents. The larvae

drift among plankton, feeding

on microscopic plants and oth­

er organisms.

A larva passes through sever­

al distinct growth stages as it

drifts along. It may be carried

some distance before settling

on the seabed, where it finally

changes into an adult brittle

star. Of the hundreds of eggs

produced by each female, few­

er than 10 offspring live long

enough to breed.

Right: The common brittle star's tube feet are arranged in double rows along the limbs.

in the water, and assess the

feel of the seabed. Because it

has no brain, its responses are

reflex actions.

• Some beds of brittle star

extend for miles across the

seafloor, with millions of brit­

tle stars forming a forest of

waving arms.

D'··· ~: NATUREWATCH

The biggest swarms of brittle

stars are found in deep water,

down to 300 feet. But you may

find brittle stars lurking under

rocks and in seaweed near the

low tidemark. If you expose

one, it will retreat because it

always hides from light. Do

~ FOOD &; FEEDING In some places the sea is thick

with planktonic organisms drift­

ing with the currents. A brittle

star feeds by simply reaching

out and gathering up tiny mor­

sels as they float past-a tech­

nique called suspension feeding. When the common brittle star

feeds, it moves its limbs through

the water and traps plankton on

a sticky mucus that oozes from

the tube feet underneath each

Left: The tube feet trap food and then pass it along a food groove to the central mouth.

not try to trap it since it is likely

that a limb will snap off.

limb. These small mobile "fin­

gers" are operated by hydraulic

pressure. When one of the tube

feet snares a victim, it bends and

transfers the prey to a mucus­

lined groove in the limb. The

flowing mucus carries the food

to the animal's mouth.

Brittle stars gather in huge

swarms at the best feeding sites,

where the seabed is swept by

strong currents rich in plankton.

The animals cling to rocks and

to one another while they comb

the water for food .

GOOSE BARNACLE

The goose barnacle is a small crustacean that spends its life hanging from objects floating in the sea. Its name comes from

an old belief that geese hatched from barnacles.

CHARACTERISTICS

Shell: About 2 in . long; made up

of 5 plates. Whitish with translu­

cent blue tinge.

Stalk: Usually 1 in . long but can

be partially retracted . Brownish

gray and leathery.

BREEDING

Hermaphrodite (has both male

and female sex organs). Cross­

fertilization occurs if another bar­

nacle is close enough.

LIFESTYLE

Habit: Collects in large groups

that attach to floating objects.

Diet: Plankton, sand hoppers,

copepods, and isopods.

Lifespan: Up to 6 years. Many

die during nauplius stage.

RELATED SPECIES

There are about 900 species of bar­

nacle worldwide, including many

other species of goose barnacle in

the suborder Lepadomorpha.

Range of the goose barnacle.

DISTRIBUTION

Found in the northern half of the Atlantic Ocean and the

North Sea.

CONSERVATION

This species and the other species of goose barnacle are all

numerous with in their range, even though marine engineers

have been trying to prevent them from gathering on man­

made objects. No conservation measures are necessary.

FEATURES OF THE GOOSE BARNACLE TH E PUPA

1. Penis: Pro­trudes into shell of another bar­nacle to deposit sperm.

2. Anus: Releases waste from the gut.

3. Gut: Stom­ach is linked to and fed by the cirri.

4. Ovaries: Situated in the fleshy stalk and connected by the oviduct.

5. Cement gland: Near the bottom of the stalk. Secretes a substance to anchor the barnacle to a floating obj

© MCMXCII IMP BV/IMP INC WILDLIFE FACT FILE'M

6. Cirri: Barnacle feeds by opening the

upper plates of its shell and extending

5 pairs of limbs, called cirri. Plankton

floating on the tide become caught in the hai rs that coat

these limbs. The cirri retreat back into

the shell , taking the prey with them.

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In its first stage of development, the goose barnacle is a tiny nau­plius larva. It builds up fat re­serves as it changes into a nonfeeding cyprid larva.

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When sailing ships dominated the seas/ goose barnacles

were a major menace because they clung to the ships /

hulls in huge numbers and greatly reduced their speed.

Goose barnacles are less of a problem today because the

hulls of modern ships are treated with a special paint

that prevents these animals from settling on the hulls.

~ CHARACTERISTICS The goose barnacle lives only in the open sea. This crustacean has a shell made up of five thin, whitish gray plates with a tinge of dark blue. It also has a long, leathery stalk, or peduncle, so it is sometimes called the stalked barnacle. One end of the stalk

[SJ NATUREWATCH Many barnacle species can be found on seashore rocks, but the goose barnacle lives only in the open sea . Large num­bers attach themselves to var-

anchors a barnacle to an object. When the goose barnacle's

shell is open, a bunch of feath­ery tentacles, called cirri, appear. The cirri are the equivalent of the legs found on other crus­taceans, and they are used to trap food.

ious objects, from buoys and pieces of wood to whales. If the object is cast up on the shore, the barnacle may still be attached by its long stalk.

~ FOOD & FEEDING The adult goose barnacle eats mainly tiny planktonic animals. It sweeps the water with its cirri to catch the plankton. Most of the cirri are arranged as two netlike scoops on either side of a basket shape. They open and close regularly, about 40 times a minute. Food particles that are trapped when the scoops close are scraped off by the remaining cirri and dragged

Left: Like other stationary animals, the goose barnacle waits for food to come near it.

Right: Goose barnacles may clus­ter together to form a large, free­floating raft.

to the barnacle's mouthparts. The goose barnacle some­

times catches larger copepods, sand hoppers, and isopods by seizing their legs with an indi­vidual cirrus.

Right: The goose barnacle's stalk may grow to an inch long. It is cemented to a floating object.

Left: The goose barnacle can survive when it is washed ashore because its strong ad­ductor muscle seals the shell tightlYt keeping the body from drying out.

I DID YOU KNOW? • In the Middle Ages, people thought that the goose barna­cle was an embryonic form of the barnacle goose, and that is how it got its name. The leg­end survived until the Euro­peans discovered the goose's Arctic breeding grounds.

~ BREEDING The goose barnacle is a herma­phrodite, having both male and female sex organs. Yet it usual­ly mates with another, nearby goose barnacle so that cross­fertilization takes place.

The barnacle's eggs hatch in­side its body, and the larvae are released into the sea. The initial larva--called a nauplius larva­looks like a water flea. It has a compound eye and three pairs of limbs with which to propel itself. After six months and sev-

Left: Goose barnacle colonies may be found on shoreline debris such as bits of plastic or wood.

• Details of the barnacle's de­velopment were revealed in 1833, when a naturalist caught immature forms and observed them as they grew into adults. • When its eggs hatch, one goose barnacle may release 1 3,000 young.

eral instars (stages of develop­ment), it becomes a cyprid larva. At this point it looks like a tiny mussel and has a pair of eyes, six pairs of legs, and a soft shell.

In the nauplius stage, the bar­nacle is mobile. By drifting on tidal currents and swimming, it can move to a new habitat. The cyprid larva attaches itself to an object by secreting a cement­like substance. After some fur­ther changes, it develops a hard shell and cylindrical cirri. The adult goose barnacle remains anchored to the same object for the rest of its life.

WAVED WHELK

CLASS Gastropoda

ORDER Neogastropoda

GROUP 6: PRIMITIVE ANIMALS .. FAMILY

'11IIIIIIII Buccinidae GENUS & SPECIES Buccinum undatum

The waved whelk may look harmless, but it is one of the main predators of the seabed. This marine relative of the garden

snail attacks and feeds on other shelled sea creatures.

KEY FACTS

SIZE

Length: Up to 3 in . near the shore.

Up to 6 in. in deep water.

BREEDING Mating: Internal fertilization .

Eggs: More than 1,000 white cap­

sules containing hundreds of eggs

are attached to a rock in a large

spongelike mass.

LIFESTYLE Habit: Predator that feeds on sea­

bed. Usually stays underwater.

Diet: Bivalve mollusks, such as mus­

sels; echinoderms, and sea snails.

Also dead or injured fish .

RELATED SPECIES

Whelks of the family Buccinidae are

found from tropical seas to cool

North Atlantic waters. They come

in many colors and sizes. There are

several other families that contain

whelks, including the dog whelks

of the family Nassariidae.

• Range of the waved whelk.

DISTRIBUTION

Found in the North Atlantic in coastal waters from 6 to 500

feet deep. Range extends as far south as the Carolinas on the

American side and Spain on the European side.

CONSERVATION

The waved whelk is caught for food and fishing bait but is so

abundant that fishing does not seem to affect its population .

FEATURES OF THE WAVED WHELK

Tentacles: Used for feeling objects. Each one has an eye at the base.

Mouth: Can be extended on a long proboscis for sucking in food.

Siphon: Draws water into the

whelk. Also detects

chemicals in the water.

Shell: Often encrusted with tiny barnacles and keel worms. The spiral lines around the shell reveal the whe lk's approximate age.

Foot: Broad and muscular. Carries the whelk across the seabed.

Operculum: Hard disk on the

end of the foot acts as a lid to seal the whelk

safely inside

its~1 ©MCMXCVI IMP BV/IMP INC. WILDLIFE FACT FILETM PRINTED IN U.SA us P 6001 12 078 PACKET 78

The waved whelk is found in coastal waters in the North

Atlantic. This whelk is a typical sea snail that prefers to be

covered by water. But sometimes it is found on the lower

part of a beach when the tide is out. It can also be seen in

fishing harbors, after it has been dredged from the seabed

in nets or caught in baskets baited with dead fish. The

waved whelk may be sold as food or used as fishing bait.

~ HABITAT The waved whelk usually lives in water 6 to 500 feet deep, of­ten in areas of muddy gravel or sand. It sometimes appears on the lower shore but is not found farther up because it dries out and dies if exposed to the air for long.

During the period of neap

DID YOU KNOW? • The genus name Buccinum is derived from the Latin word for trumpet and refers to the shape of the shell. • In the past fishermen used the empty egg capsules of the waved whelk as "sea soap" to clean their hands.

tide (when the difference be­tween high and low tide is the smal lest), the waved whelk may move up the beach . In spring, when the extreme tides come, some whelks may be left high and dry. Most, however, find the sea again or remain below the low tidemark.

• Hermit crabs use discarded whelk shells as homes. For pro­tection, a crab may place a sea anemone, which has stinging cells, on top of the whelk shell. • Waved whelks in deep wa­ters may grow to twice the size of those near the beach.

~ BREEDING After mating, the female waved whelk lays over 1,000 egg cap­sules-each containing more than 100 eggs. The capsules are embedded in a mass of albumin

(egg white) and are surrounded by a spongy casing. Many of the eggs never hatch because their contents are absorbed by others for nourishment.

Inside the egg, the body of the larva is symmetrical at first. Left: A small, hard lid on its foot seals the waved whelk in when it withdraws into its shell.

[" .'.t1 NATUREWATCH It is rare to find a live waved whelk on the seashore. Most of the shells found on the beach are empty. The whelk's egg masses are often cast up along the tide line, but they are likely to be empty as well.

A deep tide pool may con-

But near the end of its develop­ment, it undergoes a process called torsion, in which most of the body's upperpart twists counterclockwise 180 degrees . Torsion is common in most gas­tropod species. No one really knows why it happens, but one possibility is that it helps the whelk to carry its shell. When the egg case breaks, a tiny, fully formed whelk emerges. Right: The female waved whelk lays a huge cluster of egg capsules, which she attaches to a rock.

tain a living whelk creeping over pebbles and seaweed. But if the shell moves sudden­ly across the bottom of the pool, it does not contain a waved whelk. Instead, it is oc­cupied by a hermit crab that has claimed a discarded shell .

~ FOOD & HUNTING The waved whelk eats other sea snails, bivalve mollusks such as mussels and oysters, and echi­noderms such as starfish. It also eats dead or wounded fish.

It finds its prey by detecting chemicals in the water. Unlike some whelks, it does not bore through a mollusk's shell to reach the flesh. Instead, it pries

~ CHARACTERISTICS The waved whelk's hard shell varies from yellowish brown to chalky gray. It is made up of sev­

en or eight swollen whorls, with broad ribs crossed by spiral lines. The number of spiral lines re­veals the whelk's approximate age. Barnacles and bits of sea­weed often cover the shell.

Inside the shell, a fold of skin known as the mantle encloses the whelk's soft body. Glands in the mantle secrete a substance that hardens to form the shell.

The waved whelk employs its broad, muscular foot to creep

Left: A tubular siphon protrudes from the waved whelk 's body and detects chemicals.

the two halves apart, grips one half firmly with its foot, and then wedges the other up with the lip of its own she ll. It next inserts its radula (a filelike ribbon) and cuts the muscles that hold the two halves of the shell togeth­er. After it sucks out the flesh, it leaves the empty shell behind and sea rches for its next victim.

along the seabed. At the end of the foot is a shell-like operculum,

a "trapdoor" that the animal can shut when it retreats into its shell. The waved whelk uses its special columella muscle to pull its head and foot into its shell.

On its head the waved whelk has a pair of tentacles with eyes at their base. It also has a long proboscis that it can extend to suck in food . Close to the head there is a siphon, which the ani­mal uses to draw in water.

In its mouth the waved whelk has a radula, a long ribbon with rows of horny teeth . It moves

the radula like a saw when at­tacking shelled animals.

GIANT CLAM GROUP 6: PRIMITIVE ANIMALS

~--------------------------------~ ... ORDER

"11IIIIIIII Veneroida ... FAMILY ~ Tridacnidae

GENUS & SPECIES Tridacna gigas

The giant clam is an enormous shellfish that can weigh a quarter of a ton. This huge, colorful inhabitant of coral reefs feeds

by filtering microscopic plankton from the sea.

KEY FACTS

SIZES

Length: Up to 5 ft.

Weight: Up to 570 lb .

LIFESTYLE

Habit: Immobile, half-buried on

reefs or in sand.

Diet: Feeds by filtering plankton.

Obtains carbohydrates from algae

in mantle.

Lifespan: Well over 100 years.

BREEDING

Spawning: Synchronized when

conditions are right. Each giant

clam produces sperm and eggs

alternately.

• Range of the giant clam.

DISTRIBUTION No. of eggs: Several million.

Larvae: Free-floating. Drift in

plankton before settling for life in

shallow waters on seabed.

Found in shallow, clear water on coral reefs and reef flats in the

Indian and Pacific oceans.

CONSERVATION RELATED SPECIES

Tridacnid clams occur only in the

Indian and Pacific oceans. They are

closely related to the Venus clams

of North America and Europe.

Although the giant clam is not directly threatened by human

exploitation, any threat to a coral reef affects the clam as well

as the coral.

FEATURES OF THE GIANT CLAM

Valves: 2 cor­rugated hard shell halves that interlock.

Mantle: Fleshy membrane lin­

ing the valves. It contains internal body organs. Al­

gae that are in the mantle edge convert sunlight

'~l~~t\l~'~L into sugars.

OPENING AND CLOSING

The clam's valves are usually set slightly apart. When its valves are open , the clam can feed by pass­ing water into its siphons. It can also eject sperm and eggs when it reproduces .

To defend itself, the clam simply closes up by contracting a power­ful adductor muscle attached to the inside of both hinged valves.

o r--. f­LU ::.:: o ~ o r--. o ~ ;; o <0

CL (j) ::J

The giant clam is a bivalve mollusk with a wavy,

ridged shell. It is basically an enormous clam that

leads a stationary life wedged in a coral reef in the

sea. The giant clam is similar in many ways to the

coral among which it lives. Like coral, it cultivates

algae within its body tissues so that it can benefit

from the food these tiny plants make from sunlight.

~ HABITAT The giant clam can be found on coral reefs and flats in the Indian and Pacific oceans. Af­ter the clam has settled in a good site, it remains there for life. It is held to the spot by strong, silken fibers and its great weight.

The giant clam has adopted a lifestyle similar to that of cor­al. It feeds on floating organ­isms and harbors microscopic single-celled plants, or algae,

under its mantle's skin, beneath a layer of transparent cells.

The algae convert sunlight into food. During the daylight hours, they need to be in con­stant sunlight to work effec­tively. As a result, the giant clam is found only in shallow, clear water-in the same habi­tat as coral.

Right: The giant clam filters food and also has energy-making algae on the edge of its mantle.

~ FOOD & FEEDING The giant clam requires a bal­anced diet with vitamins and proteins to build its body and carbohydrates to give it energy. Its energy needs are fulfilled by algae that live in its mantle. The algae use sunlight to convert water and carbon dioxide into sugars. They use much of this food themselves, but some sug­ar leaks into the clam's body tissues and is absorbed. The clam also consumes cells of al­gae as they multiply in the sun.

Sugars produced by the algae

left: Measuring up to five feet in length the giant clam is the larg­est living bivalve.

Right: The siphon, or opening in the clam's mantle, passes water in and out of the clam.

I DID YOU KNOW? • The giant clam has small "eyes" along the edge of its mantle that respond to light. If a shadow passes over its eyes, the clam slowly closes up to protect itself from pos­sible attack. • Stories of divers getting their feet trapped in giant clams are probably untrue.

provide energy that drives the clam's water-pumping system. The clam pumps water through its body, drawing it into one siphon and ejecting it from the other. Not only does the water carry vital oxygen, but it also contains tiny organisms such as fish eggs. The clam filters and digests this waterborne food, extracting the proteins and vita­mins that it needs.

Right: The giant clam's mantle edge often protrudes when the shell valves are open.

The clam closes its shell so slowly that it is a very ineffi­cient trap. • Many giant clams provide homes for small crabs called pea crabs. A single pair of crabs lives inside each clam. They may defend their terri­tory against small invading sea creatures by eating them.

The giant clam has the same structure as any other clam. Like all bivalve mollusks, it has a shell with two plates, or valves, that are joined by a spring-loaded hinge at the bottom. They gape open naturally, but the clam can pull them shut with its powerful adductor muscle, sealing itself against enemies.

~ BREEDING From its position half-buried in sand or in a coral crevice, a gi­ant clam ejects its eggs into the water. Some eggs encounter the sperm of nearby clams, are fertilized, and grow into adults.

To improve the chances of fer­tilization, the giant clams in an area all spawn at the same time. They produce huge numbers of eggs and sperm in a few hours. Each clam alternates between producing only eggs or only

The shell's interior is lined with a thick quilt of skin called the mantle. This protrudes from the shell like fleshy lips. The linings of both valves fuse together to form a sheet that covers the in­ternal organs. There are two openings, or siphons, which serve as the clam's communi­cation channels with the water.

sperm. Correct water tempera­ture may trigger spawning, and chemical signals released by the spawning clams may then cause nearby clams to spawn.

Most of the eggs are eaten by predators. Fertilized eggs devel­op into veliger(free-swimming)

larvae. They drift with the cur­rent, feeding on algae. In a few days, the larvae settle on the seabed. If water conditions are right, they become adult clams.

SOWBUG ~~~E:::-----::==:<GROUP 6: PRIMITIVE ANIMALS

.. CLASS .. ORDER .. SUBORDER ~ Crustacea ~ Isopoda ~ Oniscoidea

Sowbugs are crustaceans, like lobsters and shrimps. But unlike their relatives, these small creatures have adapted to life

on dry land and are never found in the water.

CHARACTERI STICS length: Uo-l in. The larger species occur in the tropics . Coloration: Slate gray, reddish, or white. Some species have yel­low markings.

BREEDING Sexual maturity: 1 year. Mating season: Summer in tem­perate regions. Varies in tropical and desert regions. No. of eggs: 30-50. Hatching time: 5 weeks.

LIFESTYLE Diet: Decaying plant and animal matter; some fresh vegetation. lifespan: 2-3 years.

RELATED SPECIES There are about 4,000 other spe­cies in the order Isopoda. These are the nearest relatives of the 7 sow­bug families. They include grib­bles, sea pillbugs, sea roaches, and many parasitic forms.

FEATURES OF SOWBUGS

Thorax: Consists of 7 segments. Each segment supports a pair of equal-size legs.

Exoskeleton: Outer cover­ing. Not water­proof. Shed and replaced as a sowbug grows.

• Range of sowbugs.

DISTRIBUTION Sowbugs are found all over the world except in the Arctic and Antarctic, where they cannot survive the cold.

CONSERVATION Because they thrive in so many different habitats and climates, sowbugs are not threatened by human settlement or endan­gered in any other way.

Head: Has 2 antennae. Mouthparts contain ·1

pair of mandibles (jaws) and 2 pairs of maxillipeds

(feeding appendages).

Pillbug: A kind of sowbug that can roll itself into a ball to protect under­parts from losing moisture.

Abdomen: Made up of 6 seg­ments. The last segment has a pair of feelerlike appendages.

Body: A pillbug's body is more arched and compact than the body of a sowbug.

© MCMXCII IMP BV/IMP INC WILDLIFE FACT FILETM PRINTED IN U.S.A. 0160200791 PACKET 79

Sowbugs have colonized all parts of the world, with the

exception of the Arctic and Antarctic, where they cannot

survive the freezing temperatures. Although most sowbugs

frequent damp places, some species flourish in dry areas,

and a few species even live in deserts. All sowbugs avoid

prolonged exposure to open air and sunlight however,

for under such conditions they dry out and die.

~ CHARACTERISTICS A typical sowbug has a head, a thorax, and an abdomen. The thorax has seven segments, and each supports two short legs. The abdomen has six segments.

A sowbug molts (sheds its out­er covering) as it grows. Its skin loosens, then splits. The rear half is shed first. In three days, when the new rear covering has hardened, the front half is shed. When the new front cov­ering hardens three days later, the animal eats its cast-off skin.

A sowbug lacks a waterproof outer covering, so it cannot re­tain moisture. Some sowbugs can roll up to prevent moisture loss. Sowbugs that can do this are called pillbugs.

Most sowbugs stay in damp places to avoid drying out. They hide under stones and rotting logs, as well as in damp grass, moss, and even moist corners of houses. Some species live in forests, on grassland, and under driftwood on sand dunes.

In North Africa and the Near East, one desert species lives in burrows dug by several sow­bugs. The animals stay in the burrows by day and emerge at night to feed.

This social behavior is typical of many sowbugs. Equipped with poor vision, they secrete a scent to attract one another. The scent also repels predators such as spiders and ants.

~ FOOD & FEEDING To avoid the drying heat of the day, sowbugs feed at night or dawn. They are part of a small group of animals known as "de­composers" because they help recycle organic waste matter by eating decaying vegetation.

Sowbugs also eat growing plants but cause less damage than people think. In addition, they feed on some flesh such as

left: Because it has many legs, a sowbug can move easily over both horizontal and vertical surfaces.

DID YOU KNOW? • Sowbugs have a number of names in different places. Lo­cal names include chisel-hog, wood louse, lugdor, palmer, and roly-poly. • A pillbug is often confused with a pill millipede, which also rolls into a ball. But the latter has many more pairs of legs than a pill bug and also a

the decaying bodies of other ti­nyanimals.

Sowbugs take in moisture in different ways. Some species absorb it from the outside of the body through a system of tubes. Other species have body grooves that carry condensation from the upper surface to the gills. Still other sowbugs actual­ly drink water. Right: A pillbug protects itself from drying out by rolling its armored body into a ball.

square-shouldered appear­ance. Pill millipedes live pri­marily in woodlands. • At one time sowbugs were prescribed as medicine for various diseases of the liver and digestive system. The type of sowbug swallowed by the patient was, of course, a pillbug.

[", j NATUREWATCH

There are 200 species of sow­bug in North America. The most common species are around half an inch long. They are easy to find under rocks or decaying logs. If you expose a few, they will scurry around looking for another

moist, shady place to hide. Porcellio scaber is a common

species that can be found hid­ing under loose bark and in sand dunes. In fairly dry habi­tats, look for pillbugs. A very small specimen might be a youngster or a related species.

~ BREED I NG A male sowbug fertilizes a fe­male through a pair of open­ings at the base of each leg on her fifth segment. The sperm is stored until the female's next molt, when it is released to the oviducts to fertilize the eggs.

The female carries the eggs in a brood pouch. The large yolk in each egg nourishes the em­bryo, which undergoes all the larval stages before hatching.

The tiny sowbug develops its last pair of legs after it molts for the first time, a day after hatch­ing . Growth is slow, continuing even after sexual maturity.

left: After molting-and before its new covering hardens-a sowbug is vulnerable to attack.

PLUMOSE SEA ANEMONE

ORDER Anthozoa

FAMILY Actiniaria

~ ........... G~ROUP 6. PRIMITIVE ANIMALS ... GENUS &: SPECIES ~ Metridium senile

The plumose sea anemone appears to be harmless. But it uses its spectacular tentacles to trap and kill animals, paralyzing

them with the venom of countless stinging cells.

KEY FACTS

SIZES Height: Up to 18 in. Diameter: Up to 8 in . across ex­panded tentacles.

BREEDING Sexual: Eggs and sperm are re­leased into water, where they then combine and develop into free­swimming larvae. Asexual: New individuals may "bud" off the parent or develop from fragments of body tissue.

LIFESTYLE Habit: Attached to rocks in shallow coastal waters. Diet: Planktonic plants and ani­mals; also small sea creatures that drift or swim into its paralyzing tentacles.

RELATED SPECIES Like all other anemones, it is re­lated to jellyfish and corals. The beadlet anemone, Actinia equina,

is a close relative.

Range of the plumose sea anemone.

DISTRIBUTION The plumose sea anemone is widely distributed in shallow coastal waters as well as on rocky shores throughout the Northern Hemisphere.

CONSERVATION Marine pollution takes its toll on local populations. But the plumose sea anemone is still common throughout its range.

THE STINGING CELLS OF THE PLUMOSE SEA ANEMONE

"Trapdoor" : Nematocyst

Tentacles: Mass of small exten­sions in clusters on the top of the body column.

©MCMXCVI IMP BV/IMP INC. WILDLIFE FACT FILETM

Spring-loaded, with a hair trigger. Covers the entrance of the stinging cell 's sac.

Retracted position: Shortened, jellylike blob when anemone retracts its tentacles.

Nucleus: Re­sponsible for growth and rep rod uction of the cell.

PRINTED IN U.S.A.

coiled: There are hundreds of nematocysts in the anemone's tentacles. Each is a tiny poison

harpoon. Set on the end of a thin

flexible tube, it is stored inside

out in a tiny sac.

Nematocyst uncoiled: When

an animal brushes the tentacles , the

trapdoor opens and the barbed harpoon injects

venom into the victim.

US P 6001 12074 PACKET 74

The plumose sea anemone is found in shallow waters

throughout the Northern Hemisphere. This creature can

easily take advantage of the wealth of food that flows

past it in the ocean currents. Attached to a rock in

shallow coastql waters, the anemone simply waits until

plankton and small sea creatures drop into its trap.

~ STRUCTURE The plumose sea anemone re­sembles a flower more than an animal. It is one of the most spectacular sea anemones in northern coastal waters. On top of a long body column, feath­ery plumes of stinging tentacles surround a central mouth that opens into a stomach cavity in the column. At the base a pow­erful disk like a suction cup an­chors the anemone to a rock.

Instead of a brain, the plu­mose sea anemone has a net-

work of nerve cells throughout its body. When they sense the touch of a potential predator, they trigger a response from muscle fibers attached to the tentacles. Within seconds, the anemone draws its tentacles in­to its body, contracting itself in­to a shurt, rubbery pillar. After the danger is over, the anem­one extends its tentacles again.

Right: The anemone's form varies greatly, with clusters of tentacles around the mouth.

~ BREEDING Because its cells are not highly specialized, the plumose sea anemone can reproduce itself asexually by making new indi­viduals from "buds." Also, if the anemone is cut in half, the cells

. in both parts can reorganize to develop into two individuals.

The species does not broaden its range much by asexual repro-

Left: The plumose anemone can grow a replica of itself as a bud sprouting from its disk.

DID YOU KNOW? • The plumose sea anemone is not completely stationary. It is held to a rock by secretions from its suctionlike disk. If it settles on a poor feeding site,

~ NATUREWATCH Most plumose sea anemones live well below the low-tide level. But you may find one during a very low spring tide if you search among seaweed on rocks or pier pilings. Out of water it looks like a blob of jel-

duction, so it also reproduces sexually. It ejects great quanti­ties of eggs and sperm into the water. Only a small proportion of the sperm fertilizes the eggs.

The larvae that hatch from the fertilized eggs look like tiny free­swimming jellyfish. Those that survive settle on the seabed and develop into adults.

Right: The plumose sea anemone defends itself by simply retracting its tentacles.

it can unstick itself and move. • At up to 18 inches high, the plumose anemone is one of the largest anemones found in northern coastal waters.

Iy, with its tentacles tucked in­side to prevent drying out.

When submerged, the plu­mose sea anemone unfurls its tentacles. You might see this spectacular sight in the deeper rock pools at low tide. -----1

~ FOOD &: FEEDING The plumose sea anemone con­sumes plankton, including the eggs and larvae of fish and in­vertebrates. It also eats other small sea creatures like shrimp.

Attached to a rock, the anem­one spreads its tentacles and waits for prey to drift by. The tentacles are armed with nemo­

tocysts, stinging cells that are like tiny poison harpoons. When a victim brushes against the ten­tacles, the harpoons shoot out and inject venom into its body.

Left: The mass of tiny tentacles waving in the currents draws objects into the plumose sea anemone's cen­tral mouth. The anemone digests any­thing that is edible.

Each stinging cell does little damage by itself. However, as the anemone's tentacles em­brace the prey, the combined venom of the cells paralyzes the victim almost instantly. The ten­tacles then guide the prey into the anemone's central mouth, which closes to let the digestive juices work. After digesting the prey's soft parts, the anemone opens its mouth, ejects any re­mains, and prepares to ensnare another meal.

BLUE CRAB

ORDER Oec;apoda

GENUS &. SPECIES Callinectes sapidus

The blue crab is one of the largest and most colorful American crabs. This marine creature can swim very well, aided by

the paddle-shaped tips of its last pair of walking legs.

SIZE

Body width: 5-9~ in . after reaching

sexual maturity.

BREEDING

Sexual maturity: 12-16 months.

Mating season: June to October.

Spawning season: May to October.

No. of eggs: 750,000-2,000,000.

Hatching time: 2-3 weeks.

LIFESTYLE

Habit: Solitary. Lives in quiet inshore

waters and migrates into deeper wa­

ter for the winter.

Diet: Plant matter, clams, worms, and

dead marine animals.

Lifespan: 3 years.

RELATED SPECIES

The blue crab belongs to the family

Portunidae, which includes the swim­

ming crabs. The lady crab, Ova/ipes

ocellatus, is a close North American

relative of the blue crab.

FEATURES OF THE BLUE CRAB

• Range of the blue crab.

DISTRIBUTION

Found in estuaries and bays along the coast from Nova Scotia

south to Mar del Plata in Argentina, as well as in Bermuda.

CONSERVATION

The blue crab is an abundant animal in inshore waters through­

out its range, although it is heavily fished . Like all marine crea­

tures, it suffers from pollution in the ocean and coastal waters.

STAGES IN DEVELOPMENT

Adult: As its name im­plies, the full-grown crab is boldly marked with blue. Both sexes have this coloring .

Swimming legs: The two back legs are paddle-shaped, enabling the animal to swim fai rly swiftly.

'" MCMXCII IMP BV/IMP INC WILDLIFE FACT FILEIM

vision. Can also be ret racted.

Claws: Stout; used both for defense and to capture food .

Zoea larva: Almost mi­croscopic, it floats freely in the water.

Megalops: Develops from zoe a larva. It soon settles on the bottom and turns into a recognizable crab.

----------~------------ ----PRINTED IN U.S.A 0160200981 PACKET 98

The blue crab is found in inshore waters along the Atlantic

coast from Canada to Argentina. It is the most important

commercial crab in North America, where the annual catch

is about 300 million pounds. A freshly caught crab must

be handled carefullYt because it is extremely agile and

has powerful pincers that can inflict a painful wound.

~ HABITS The blue crab spends the major­

ity of its time searching for food

in eelgrass beds in the shallow,

sunlit waters of bays, estuaries,

and lagoons. When this animal

is scavenging for food or hunt­

ing prey, it is helped by its oar­

like rear legs, which allow it to

move as fast as three feet a sec­

ond. This speed also enables it

to escape its predators, includ­

ing large fish as well as herons

and other water birds.

The blue crab is a skillful swim­

mer. It usually moves sideways

or backward, but it sometimes

hovers in one place in the water.

When the weather turns cool

in the fall, blue crabs migrate

from the shallows into deeper

water, where the temperature

remains more or less constant.

The females tend to migrate in­

to deeper water than the males.

In spring, both sexes return to

the shallow inshore waters.

Above: The favorite habitat of the blue crab is an eelgrass bed in the shallow water of a bay or estuary.

Right: In its threat display, the blue crab spreads its formidable claws, which can inflict a painful pinch.

~ FOOD & FEEDING The blue crab is mainly a scav­

enger, feeding on any dead ma­

rine creature it finds. But it also

sometimes uses its sharp, pow­

erful claws to prey on worms,

clams, or other marine animals.

Because the blue crab can swim

rapidly and has keen eyesight, it

can catch a variety of creatures

that other crabs must pass up. It

is so fast that it can even capture

shrimp and minnows.

The blue crab often includes

plant matter in its diet. It feeds

on tender leaves of eelgrass as

well as soft seaweeds.

I -:,~ NATUREWATCH The blue crab rarely comes

to the surface of the bay or

estuary in which it lives. As

a result, you are unlikely to

find one unless you go out

in the water with a bait line

or fishing net.

Like all crabs, the blue crab

molts (sheds its shell) several

times before it reaches full

size. Its discarded shell usu­

ally washes ashore, where it

is often mistaken for a crab

that has died. The shell re­

tains its color for some time,

and it makes an interesting

souvenir of a beach visit.

~ BREEDING Blue crabs can mate at any time

during the warm months, from

June to October. Mating occurs

when an adult female has just

molted and her shell is still soft,

so the male can penetrate her.

After mating, the female be­

gins her migration into deeper

water. She stores the sperm in

a special chamber in her body

until she returns to the inshore

waters in spring. Then she pro­

duces her eggs, fertilizing them

with the stored sperm. A single

female may produce up to two

million eggs.

The female carries all the eggs

DID YOU KNOW? • The scientific name of the

blue crab is an apt description

of this creature. Callinectes is

from the Greek for "beautiful

swimmer," and sapidus is Lat­

in for "tasty."

• Several animals are adapted

for living on or in the body of

the blue crab. Three species

of barnacle hitchhike on the

shell of this crab. There is also

a type of worm that lives only

under her body until they hatch

in two or three weeks. Each be­

comes a free-swimming zoea larva. After it has molted sever­

al times, the zoea larva becomes

a more crablike animal called a

mega lops because of its big eyes.

The mega lops settles into the

eelgrass. Gradually, after sever­

al more molts, it assumes the

shape of a small crab. By the

age of 12 to 16 months, the

young crab is sexually mature

and ready to mate.

Above: As it grows, the blue crab sheds its shell. The new shell hard­ens within a day or two.

among the blue crab's gills.

• Although the blue crab is

generally found in relatively

shallow coastal waters, it is

occasionally caught in water

almost 300 feet deep.

Maryland and Virginia .

• Chesapeake Bay is the cen­

ter of the blue crab industry.

Every year about 100 million

pounds of crab are caugh:Jin this large estuary that lies in

-----

VIOLET SEA FAN

ORDER Gorganacea

FAMILY Plexauridae

GROUP 6: PRIMITIVE ANIMALS ... GENUS·&: SPECIES ~ Muricea chamaeleon

The violet sea fan looks like a plant, but it is actually an animal. This colony of individual polyps is attached to a branching,

twiggy support that is set firmly on the seabed.

KEY FACTS

SIZES Width: Up to 20 in .

Height: Up to 3 ft.

BREEDING Sexual: Polyps release sperm to

fertilize eggs. These become mo­

bile and establish new colonies.

Asexual: New polyps grow buds

to build up a colony.

LIFESTYLE Habit: Fixed to rocks and firm sur­

faces on the seabed at depths of

65-100 ft. Diet: Minute planktonic animals

strained from the water.

Lifespan: 30 years or more.

RELATED SPECIES There are many species of sea fan,

including the white horny coral,

Eunicella verrucosa. They are close­

ly related to other corals as well as

to sea anemones.

Range of the violet sea fan.

DISTRIBUTION The violet sea fan is found in the warm currents of the Gulf

Stream in the eastern North Atlantic.

CONSERVATION Many Mediterranean and tropical sea fans are endangered by

collecting for commercial trade. For this reason the violet sea

fan's population is decreasing. In addition its decline has prob­

ably been accelerated by the effects of pollution.

FEATURES OF THE VIOLET SEA FAN

Polyp: Similar to a tiny sea anemone. Each polyp is attached to the violet sea fan's "twigs" and to the network of tubes within the fan's structure. Polyp can be extended and retracted.

Holdfast: A gripping base that holds the fan firmly to a rock.

©MCMXCVI IMP BV/IMP INC. WILDLIFE FACT FILETM

Tentacles: 8 feathery arms, visible when the polyp is extended. Armed with numerous stinging cells.

PRINTED IN U.S.A. US P 6001 12077 PACKET 77

Sea fans are intricate, fragile-looking corals that are

composed of many hundreds of tiny polyps. Using their

feathery, stinging tentacles, these polyps feed by straining

microscopic creatures from the ocean currents. Because the

polyps are linked to one another by a network of tubes, the

entire sea fan colony shares the benefits of a single catch.

~ STRUCTURE A sea fan is a type of coral. It is

not one animal but a colony of

individual polyps linked togeth­

er by a mutual support system.

Approximately one-tenth of

an inch high, each polyp has

eight feathery tentacles to trap

food and to absorb oxygen. A

polyp does not depend only on

its own efforts to survive, how­

ever, because it is part of a net­

work of tubes that acts as a food

distribution system. Nutrients

absorbed by one polyp are thus

shared by the others, ensuring

the health of the entire colony.

In many sea corals, polyps oc­

cupy cavities in a rocklike skele­

ton. But violet sea fans are very

different. Instead of living inside

a strong supporting structure,

the polyps and their network of

tubes are attached to the out­

side of a branching, twiggy sup­

port made of a horny material

called gorgonin. The "twigs" all

branch out in the same plane,

creating the flat, fanlike effect

that gives the violet sea fan its

name. The "trunk" is rooted to

a rock with a gripping disk that

is called a holdfast.

~ BREEDING The polyps of the violet sea fan

produce both eggs and sperm.

But the colonies cross-fertilize

each other by releasing sperm

into the water and letting it drift

away in the current. Each violet

sea fan draws in the sperm of

neighboring sea fans.

The sperm cells pass into the

body cavity of a polyp and fer­

tilize the eggs inside. Each egg

develops into a microscopic in­

dependent larva that eventual­

ly emerges from the mouth of

the polyp. It propels itself in the

water by beating a fringe of mo­

bile hairs called cilia.

Left: The white horny coral, Euni­cella verrucosa, is closely related to the violet sea fan.

DID YOU KNOW? • Tropical relatives of the violet

sea fan may grow over 1 0 feet

wide and have a lifespan of

more than 100 years.

• The stinging polyps of a sea

fan make it an unpopular prey

animal. However, sea fans are

often preyed upon by Tritonia

Carried by the current, the

larva may drift a long distance

before resting on the seabed,

where it changes into an adult

polyp. It then starts to build a

colony by "budding" -grow­

ing new polyps that are con­

nected by a horny skeleton and

a network of tubes. In 30 years,

the sea fan may grow three

feet high, with hundreds of

genetically identical polyps.

Every season, these polyps

produce eggs and sperm. As

a result, it is possible for cross­

fertilization with other violet

sea fans to take place.

Right: When breeding, the violet sea fan extends its polyps to release clouds of sperm cells.

odhneri, a small pink sea slug

that is camouflaged to match

the polyps. This aquatic mol­

lusk seems to be immune to

a sea fan's venom. In fact, it

even seems to use the sting­

ing cells, transferring them to

its own skin to repel attackers.

~ FOOD & FEEDING The individual polyps of the vio-

let sea fan feed like sea anem­

ones, preying on tiny floating

animals that drift in the sea.

Each polyp has many stinging

cells called nematocysts. These

tiny, barbed poison darts shoot

out when an animal brushes

against the polyp's tentacles. If

enough darts penetrate the vic­

tim, it is paralyzed by the ven­

om and unable to resist when

moved by the tentacles into the

Left: Feeding like a mass of small, linked sea anemones, the violet sea fan seizes prey from a wide area.

polyp's central mouth. After the

prey reaches the stomach cavity

and is digested, the nutrients

pass into the tube network to

nourish the rest of the colony.

The massed tentacles of the

colony form a net in the water

to trap food over a broad area.

But the net only works if there is

a continuous water current flow­

ing through it. The violet sea fan

is most abundant where there

are steady currents in deeper

water. It is too fragile to survive

the battering it would receive in

coastal waters.

GREAT BLACK SLUG

... PHYLUM ~ Mollusca

... CLASS ~ Gastropoda

The great black slug is a harmless animal that spends the day hidden in dense vegetation. It emerges at night and after

rain to feed primarily on decaying plant matter.

SIZE

Length: 6 in . when fully grown .

BREEDING

Sexual maturity: 1 year.

Mating: Wet summer nights.

Eggs: White to brown; less than

X in . long. Laid in clusters of up

to 150.

Hatching time: 4-6 weeks. May

overwinter if laid late in the season.

LIFESTYLE

Habit: Usually active by night but

emerges after rain in day. Burrows

underground in cold or dry weather.

Diet: Rotting and fresh plants.

Some animal matter such as feces

and rotting carcasses.

Original range of the great black slug.

DISTRIBUTION

Lifespan: Up to 3 years .

The great black slug is common throughout Europe. It was

accidentally introduced to North America and has started to

spread there.

RELATED SPECIES CONSERVATION

The common garden slug is a close

relative. Other European slugs in­

clude the great gray slug and the

shield slug.

Despite the variety of pesticides used by farmers and gardeners,

the great black slug is flourishing throughout its range.

FEATURES OF THE GREAT BLACK SLUG

Mantle: Slightly raised with a grainy texture. Contains most of the slug 's organs, including the lung .

Tentacles: Used for locating food . Each longer tentacle has an eye on the end, which probably distinguishes only light and dark.

Sole: Muscular and lubricated with

mucus. Wavelike movements pass up

the sole to propel the slug forward.

Breathing pore: Air is taken in and expelled through this

hole and passes into the simple

lung cavity with­in the mantle.

(~ , MCMXCII IMP BV/IMP INC WILDLIFE FACT FILE TM PRINTED IN U.S.A

DEFENSE AND COLOR

Coloration: Differs greatly among individuals. In addition to black, Arion atermay be brick red , dark brown , or even pale orange.

0160200581 PACKET 58

The great black slug is related to the snail, but it does not

have a shell. Without a shell, the slug is more exposed to

the sun and to the cold. But, unlike the snail, it does not

need to find calcium to build a shell. As a result the slug

can live in a greater variety of places-anywhere that

provides it with enough food and moisture to survive.

~ HABITS At dusk the great black slug glides out of its daytime refuge

to begin its nightly search for food . This soft-bodied creature

may become dehydrated if it is

exposed to the sun. It appears

in daylight only if the ground is thoroughly soaked by rain .

Most of the great black slug's organs are contained under its

mantle-the raised, saddlelike structure behind its head . Its

lung is a simple cavity lined with blood vessels that takes

in air through the conspicuous

hole on the front right side of the mantle.

Because it has no shell, the

great black slug is vulnerable

Right: If you watch a slug for a while, you may see its breathing hole open and close.

to cold and drought. It bur­rows deep into the soil during

cold winters and hot, dry sum­mers. But, without a shell, the

slug can thrive in sandy places and on acid moors where the

soil does not contain the calci­um (lime) that snails need to build their shells.

Right: The great black slug feeds on mushrooms and any rotting plant matter it can find.

~ BREEDING The great black slug is a her­maphrodite-it possesses both male and female organs. But

it still must mate for its eggs

to be properly fertilized. In the mating ritual, a pair

of slugs circle one another for

some time before entwining their bodies to transfer sperm, which are contained in small

packages called spermato­

Left: The great black slug is not always black and often has a black-flecked orange "skirt."

phares. The eggs are fertilized

inside the slug'S body and laid soon after mating . They are buried in loose soil, where

they remain for several weeks, or even throughout the win­

ter, safe from rain and frost. In the spring they hatch, pro­

ducing infant great black slugs that are perfect miniatures of

their parents.

Right: The slug lays its tiny white eggs in batches. The eggs' hard shells keep them from drying out.

DID YOU KNOW? • The great black slug is often tive at cushioning sharp sur-host to tiny mites that crawl faces that the slug can crawl

1 to- ,.J NATUREWATCH

all over its body and feed on over the edge of a razor blade its mucus. without being harmed.

• The great black slug avoids • The slug's silvery trail can be being out in the rain and waits its downfall. A snake may fol-for it to stop before emerging. low the trail and eat the slug it

L The slug's mucus is so effec- _ finds at the e_nd_ o_f _it. ___ ----I

Great black slugs are most often seen after a heavy rain

when the ground is soaking wet. If a person's shadow falls

over the slug, it may instinc-tively shy away. If you touch a

tentacle, the slug will retract

~ FOOD &: FEEDING Despite what many gardeners

think, the great black slug is not the main cause of damage to

vegetables. This slug prefers to

eat rotting plant and animal matter that has been softened

by the processes of decay. But if no dead matter is available, it

feeds on tender young leaves,

seedlings, and soft fruit. The great black slug finds its

food by smell and taste, rather

~ MOVEMENT The bottom of the great black

slug is a long, muscular sole, lu­

bricated by mucus secreted by a gland under its tail. The slug

appears to glide forward with no effort, but in fact it moves in

a series of waves that travel for­

ward along the sole.

it and may turn aside. It uses its tentacles to feel for obsta­

cles, and it may assume your finger is an obstacle. Prod it a

little more firmly, and it may contract its whole body into

a tight, hard lump.

than by sight. It uses its sensitive tentacles to test if something is

edible. When it finds a suitable morsel, it uses its radula--a filelike "tongue" studded with

sharp teeth for grating tough

plant tissue. The radula grows

continuously, and each new

section is fully equipped with teeth. As the teeth move for­ward, they wear down and

finally fall off at the tip.

The slug keeps lifting part of its

sole and putting it down a little farther forward. These move­

ments ripple up the sole in a

continuous process. The sticky mucus helps the slug cling to

smooth surfaces and protects it when it moves over rough areas.