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.
0160200631 PACKET 63
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.