Clams have two shells that are joined together by a hinge. The shells are made of calcium carbonate, which is the same material that makes up pearls. Clams also have two adductor muscles, which are used to close the shells. When the adductor muscles relax, the shells open.

Clams are filter feeders. They use their gills to filter plankton and other small organisms from the water. Clams also have a digestive gland, which is used to break down food.

Clams are important members of the marine ecosystem. They provide food for other animals, such as fish, crabs, and birds. Clams also help to clean the water by filtering out pollutants.