A thin tissue that adheres to the inner surfaces of the shell,
called the mantle, and a thickened rim of muscular tissue at the mantle
edge deposit new shell material at the shell edge. Rings on the shell
indicate how many years old a clam may be.
Certain kinds of clams, in early stages of life possess a gland
that produces a thread-like material (byssus) that serves to anchor
them to grains of sand or rocks. Other types of clams lack a byssal
gland and use the foot to burrow into the seabed. As the clam grows,
its wedge-shaped foot, which expands and contracts as it moves, becomes
more important as a burrowing tool.
Eggs and sperm are released into the water seasonally,
generally in mid-summer when water is warm and planktonic food is
abundant. After fertilization of an egg, cellular division produces
larvae and eventually tiny clams that settle to the bottom. In a few
species, the final stage is completed within the mantle cavity of the
The oceanic surf
clam is the most important commercial species.
The largest clam of the U.S. east coast, it sometimes reaches a shell
length of more than eight inches. Landings of surf clams in New Jersey
and Virginia account for about half the total U.S. annual landings of
all clam species. The surf-clam catch in recent years--in shucked
meats-- ranged from about 41 to 63 million pounds.
They are dug from the intertidal flats of bays and
estuaries at low tide in New England, using a short-handled fork to
obtain clams living in burrows six to ten inches below the surface. In
Chesapeake Bay, because the beds are mostly subtidal, a hydraulic
dredge washes clams from the bottom and onto an endless belt that
conveys the clams to the dredge boat.