Dr. Steve W. AltstielNaples High School

Phylum Molluska: over 100,000 species Second-largest animal phylum. Examples: chitons, clams, snails, slugs, and

squids. Some of the shells are highly valued by collectors.

◦ From seashell collections we have learned much of what we know about this group.

Gastropods (snails)

Bivalves (oysters, clams)

Cephalopods (octopus)

The foot is a muscular organ, shaped and used differently by different species.

A clam uses its hatchet-shaped foot for digging. Clams and oysters belong to the class

A snail has a flat foot it uses for crawling.

◦ Because its stomach is in its foot, it is named Gastropoda, “stomach foot”

The foot in octopus and squids is modified into many tentacles that are attached to the animal’s head.

◦ Octopus and squids use their tentacles for moving and for grasping and holding the prey they capture for food.

The area of the mollusk called the “mantle” makes the shell for the animal (if it has a shell).

Mantle creates the colors and patterns on the shells.

The shell is an exoskeleton, even though it is completely surrounded by soft tissue in some mollusks. Be cause the shell is continually produced, it grows with the animal.

Produces 8 separate plates that cover the body. ◦ Have joints between each of these plates to allow

for it to curl up in a ball.

Mantle in bi-valves make two distinct shells.

Mantle in gastropods produce a single shell in a sprial shape.

Mantle cannot be seen, since it is the inner layer of the shell.

Yes, they do have a small shell.◦ But the mantle is opposite and covers the shell

instead of being inside the shell.

◦ This shell is inside their bodies and is called a pen (pen… ink… pen… ink)

Nudibranchs or sea slugs are gastropods that don’t produce a shell

Are all soft-bodied.

Radula: rasplike tounge in the mollusk’s mouth. Herbivorous (plant-eating) snails have a mouth

with radula containing many rows, each row with five to seven complex teeth.

The snail uses its radula like a file, scraping off small bits of food.

Snails called cone shells are carnivorous (meat-eating) hunters that produce venom in glands near the mouth.

Their radulas are shaped into long, hollow teeth, which they thrust one at a time into their prey like harpoons.

A barbed radular tooth fires through the proboscis, an extension of the mouth.

It pierces the prey, paralyzing it with venom and preventing its escape.

C:\Documents and Settings\marcella.williams\Desktop\Snail Mouth.qtl

The cone shell “swallows” the prey by engulfing it with its proboscis.

Some snails produce a poison strong enough to kill humans who handle them carelessly.

Their poison is a neurotoxin, one that attacks and destroys nerves.

The class of mollusks called Bivalves includes clams, oysters, mussels, and scallops.

Foot size varies among marine bivalves. Clams have a big hatchet-shaped foot for moving

about and for burrowing in mud or sand.

Clams: large foot to dig deep in sand

Oyster (and mussels):small foot because these animals attach themselves to hard objects early in life and do not move around.

Scallops don’t use their small foot to move around either.

They swim by jet propulsion, clapping their shells together and forcing water out the rim.

Water enters and leaves a bivalve by way of two tubes called siphons.

One siphon takes in water while the other expels water and wastes.

Water taken in contains oxygen and food particles consisting of detritus and plankton.

As the water flows across the gills, oxygen and carbon dioxide are exchanged.

Mucus on the gills traps microscopic food particles, and tiny hair-like cilia on the gills move the food-laden mucus toward the mouth.

Liplike structures called palps help sort the food and direct it into the mouth.

Bivalves do not have a radula. The food suspended in mucus moves through the digestive organs, which break it down and absorb it.

In some bivalves, such as oysters, mantle tissue secretes a pearly substance that coats any irritating particles—bits of gravel, for example—that lodge between the mantle and the shell.

As coats of this substance build up they form a pearl.

Bivalves such as clams, oysters, and scallops are valuable as food;

They make up a major share of the marine invertebrate cash crop.

Except for the shell, bivalves can be eaten whole.

But when water in which they grow becomes polluted with chemicals or disease organisms, bivalves should not be eaten.

At certain times of year, for example, microscopic organisms called dinoflagellates multiply rapidly in the enclosed waters of bays and estuaries.

When they grow so thick that the pigment in their bodies makes the water look red, the phenomenon is called a red tide.

Toxic substances produced by dinoflagellates can concentrate in the clams and oysters that use them as food.

Although the bivalves are not harmed, the toxin attacks the nervous system of humans who eat the clams and oysters.

This “paralytic shellfish poisoning” can be fatal to humans

Some people have died after eating just one clam or mussel, others after eating many--each with a small amount of poison.

You cannot tell whether the dinoflagellates are present by looking at the water with your naked eye.

Signs and symptoms of PSP most often occur within 10 to 30 minutes after eating affected seafood. Problems can include nausea, vomiting, diarrhea, abdominal pain, and tingling or burning lips, gums, tongue, face, neck, arms, legs, and toes. Later problems may include shortness of breath, dry mouth, a choking feeling, confused or slurred speech, and lack of coordination.

a specialized foot used in digging, grasping, or creeping.

a mantle that covers the soft body, encloses the internal organs, and, in many species, produces a shell. Not all mollusks produce a shell.

a radula, which in most species is a rasp-like scraping organ used in feeding.