A bivalve shell-fish found in many seas, one species being the common edible clam abundant in the United States, and much used as food. There are many varieties-as long clam, round clam, sea clam, little-neck clam, and giant clam. The long clam burrows in the sand with the muscular organ usually known as its foot. Its shell grows at the hinge, and increases as fast as the animal grows, The giant clam is an inhabitant of the China Sea and South Pacific, and is the largest known bivalve mollusc, the shells being known to measure 2 feet in length and weigh 500 lbs.