A clam is a bivalve mollusc. There are freshwater and marine varieties, those that live buried in sand, silt, or mud, or cement themselves to a substrate or are free-living, those which even as adults are nearly microscopic and others, such as the giant clam, which can weigh 200 kilograms. Some have lifecycles of only one year, while at least one has been discovered that may be over 500 years old. They do not have heads and most are blind but some, such as the scallops, have rudimentary eyes. Though a common food item, many species of clam are too small to be useful as food, and not all species are considered palatable. However, all clams have two calcareous shells or valves, and all are filter feeders.
In culinary use, within the eastern coast of the United States, the term "clam" most often refers to the hard clam Mercenaria mercenaria. It may also refer to a few other common edible species, such as the soft-shell clam, Mya arenaria, and the ocean quahog, Arctica islandica. Another species which is commercially exploited on the Atlantic Coast of the United States is the surf clam Spisula solidissima. Scallops are also used for food.
Clams can be eaten raw, steamed
. They can also be made into clam chowder or they can be cooked using hot rocks and seaweed in a New England clam bake.
In Italy, clams are often an ingredient of mixed seafood dishes, or are eaten together with pasta and Spaghetti
. The more commonly used varieties of clams in Italian cooking are the Vongola
(Venerupis decussata), the Cozza
(Mytilus galloprovincialis) and the Tellina
(Donax trunculus). Though Dattero di mare
(Lithophaga lithophaga) was once eaten, overfishing drove it to the verge of extinction (it takes 15 to 35 years to reach adult size and could only be harvested by smashing the calcarean rocks that form its habitat) and the Italian government has declared it an endangered species since 1998 and its harvest and sale are forbidden.
Clams are eaten more in the coastal regions of India, especially in the Konkan, Kerala, Bengal, and Karnataka regions.
In the south western coast of India, also known as the Konkan region, Clams are used to cook curries
) and side dishes, like Tisaryachi Ekshipi
, which is clams with one shell on.