A clam is a kind of mollusk that has a shell divided
into two pieces called valves; in other words, a clam is a bivalve mollusk.
The word "clam" has no real taxonomic significance in biology. However in
the USA the word can sometimes be used to mean any bivalve mollusk. It can
also be used to mean a bivalve other than an oyster, mussel, or scallop, and
that has a more-or-less oval shape, or a freshwater mussel (Merriam-Webster
Dictionary.). The word clam is also often used to mean any one of many
edible bivalve species which live buried in sand, hence, "digging for clams"
or clam digging.
Not all edible clams are round or oval in shape: the
razor clam has an elongated shell whose shape suggests a straight razor.
Coming from the east coast, New York to be exact, I am familiar with the
clams we have here:
Hard-shell clams: They have hard tightly closed
shells. Varieties include:
Quahogs - they are about 3" or more across
and are good for soups/chowders or for the various stuffed clam recipes.
Cherrystones - they are about 2 1/2" across and are good eaten raw or
Littlenecks - they are less than 2" across and are good eaten
raw or steamed. (This is my favorite steamed clam)
You can find these in your grocer listed as "Steamers" and are between 1
1/2" to 3". I think the smaller sizes are more tender.
people don't go out to dig clams but rather buy them, you should look for
clams that are closed and DO NOT SMELL. When you get them home you may want
to clean (purge) them. You can do this by:
Rinse the clams well in
cold water and scrub the shells
Soak them in a bowl of cold water -
do not use salt or sea water. I have read that you can add a tablespoon of
cornmeal or flour to help the clams purge out any dirt but I have yet to try