.]], Tridacna maxima.]] Lima, Peru.]] A clam is a kind of mollusc that has a shell divided into two pieces called valves; in other words, a clam is a bivalve mollusc. The word "clam" has no real taxonomic significance in biology. However in the USA the word can sometimes be used to mean any bivalve mollusc. 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 (). 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. 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 researc