Clams are a very diverse group of bivalves in that there is notable variation
in the shape, size, thickness, colour and degree of sculpturing of the shell from
one species to the next. The one feature that all clams have in common is
that they burrow into the sea-bed. Consequently, both shell and body (see
below) display modifications necessary for this type of existence. The quahog
clam, Mercenaria mercenaria, has a thick, triangular shell