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 steamed
Littlenecks – they are less than 2″ across and are good eaten raw or steamed. (This is my favorite steamed clam)
Soft-shell clams: 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.
Since most 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