Mollusks

Have you ever walked along the beach collecting shells? If so, you are already familiar with mollusks. These shells may have belonged to oysters, clams, snails, or mussels. There are about 40,000 kinds of mollusks, which makes it the next to the largest animal group.

Photos Jack2205

Learn more about the group of animals that live in the ocean and have shells.

Small to Giant

All mollusks have soft bodies. Most of them have a distinct head plus a muscular foot. The foot, along with the soft body is an important characteristic that distinguishes them from other invertebrates. Most of them have shells to protect their bodies.

Most mollusks live in the sea. Some live in fresh water, and a few kinds are terrestrial, or land-dwellers. They range in size from small snails, less than two centimeters long, to the giant squids that may be more than 18 meters long. The giant clams of the South Pacific may weigh as much as 225 kilograms each.

One group of mollusks is known as the bivalves. (clams, scallops, and others). These animals have two shells that are hinged together. The shells can be opened or closed by strong muscles. Bivalves are filter feeders. They draw water into their shells, and as the water passes over their gills, food particles in the water are trapped. The food is then passed to the mouth and eaten.

Clams, oysters, and most other bivalves don't have eyes. But scallops have a hundred blue eyes along the edge of their shell. These eyes enable the scallops to distinguish between light and dark.

Snails have a single shell that is usually coiled or spiraled. They have a tongue that is covered with toothlike bumps, called a radula. Using the radula, the snail cleans off the algae that grows on fish aquarium glass. Most snails have eyes at the tips of their tentacles.

Ink Squirters

The group of mollusks that includes octopuses (in the picture), and squids, have no shells. They protect themselves by squirting ink into the water. This confuses their enemies and gives them enough time to escape danger. They grab and hold food with their arms, or tentacles. They also have a sharp beak which they use to break open clam shells. Squids have well-developed humanlike eyes that can form distinct images.

Oysters, clams, scallops, mussels, snails, and squids are examples of mollusks eaten by people. If you have never tasted one, why not try it?