In the United States, "clam" can be used in several different ways: First, as a general term covering all bivalve molluscs. The word can also be used in a more limited sense, means that of cave sediments bivalves, rather than those attached to the substrate (such as oysters and mussels), or those who can swim, like scallops. In addition, the mussels can be used in a more limited sense, refers to one or more varieties of commonly consumed marine bivalves, in the phrase clam chowder, which means that shellfish soup usually clams . Many edible bivalves are roughly oval-shaped; however, the Pacific razor clam has an elongated, parallel-sided shell, the shape of the show, an old-fashioned straight razor.
In the United Kingdom, "clam" is one of the common names of various species of marine bivalve mollusc, but it is not used as a general term to cover edible clams that burrow, and it is not used as a general term for all bivalves.
Numerous edible marine bivalve species live buried in sand or mud, and respire by means of siphons, which reach to the surface. In the United States, these clams are collected by "digging for clams" or clam digging.
In October 2007 an Arctica islandica clam, caught off the coast of Iceland, was discovered to be at least 405 years old, and was declared the world's oldest living animal by researchers from Bangor University; it was later named Ming.
Some species of bivalves are too small to be useful for food and not all species are considered palatable.
The word "clam" has given rise to the metaphor "clam up", meaning to refuse to talk or answer, based on the clam behavior of quickly closing its shell when threatened. A "clamshell" is the name given to a container consisting of two hinged halves that lock together. Clams have also inspired the phrase "happy as a clam", short for "happy as a clam at high tide" (which should be happy because it cannot easily be dug up and eaten).
A clam's shell consists of two (usually equal) halves, which are connected by a hinge joint and a ligament which can be external or internal.
In clams, two adductor muscles contract to close the shells. The clam has no head or eyes, though scallops are an exception of this rule. Clams do have kidneys, a heart, a mouth, and an anus.
Clams, like most molluscs, also have open circulatory systems, which means that their organs are surrounded by watery blood that contains nutrients and oxygen.
Clams feed on plankton by filter feeding. Clams filter feed by drawing in water containing food using an incurrent siphon. The food is then filtered out of the water by the gills and swept toward the mouth on a layer of mucus. The water is then expelled from the animal by an ex-current siphon.
Clams begin as a shellfish the size of a grain of sand when born. It has a natural glue on it that causes it to connect to other shells or things on the bottom at the bottom of the river. Once a clam is secure, it feeds on the plankton, as stated, and moves with the tide. It takes a clam 24-30 months to become harvestable.
