A clam is a type of shellfish. Clams can be found in saltwater and freshwater. Clams eat plankton, and are eaten by small sharks and squid. Clams can be eaten by people. They may be found on menus in restaurants that serve seafood. Clams are a fairly common form of bivalve, therefore making it part of the phylum Mollusca. There are many clams in the ocean, but some can also be found in some lakes, streams, and rivers.
Clams have indeterminate sensory capabilities as they have been documented deciding to eat salt. 
Clams have a burrowing foot that they use to dig down into the sand or mud to hide. If you go to the beach and see little holes that appear in the sand each times the waves go away, it is probable that clams made them. Scientists classify clams by how far down they dig and what kind of surface they dig into. Some burrow less than an inch under the sand, while others dig several inches below the surface.
The shell has 3 layers. The top one is called mother-of-pearl because it is a coating of pearl material.
A living freshwater clam can work like a filter in fish tanks to keep the water clean.