Clam Fact:
Clams are shelled marine or freshwater mollusks belonging to the class Bivalvia. The term “clam” has no taxonomic significance in biology, but is often used to refer to any bivalve (a mollusk whose body is protected by two symmetrical shells) that is not an oyster, mussel, or a scallop, and that has a more-or-less oval shape. Clams can live up to 150 years old - or perhaps longer (science suspects that some larger quahogs found off the East Coast of the US may be 200 years old).
A Clam can be hard-shelled or soft-shelled, according to the degree of calcification of their shells, according to species. They are eaten raw, steamed, boiled, baked or fried, again (often) according to species.
Source: Clam Facts