cockle common name applied to the heart-shaped, jumping or leaping marine bivalve mollusks, belonging to the order Eulamellibranchia. The brittle shells are of uniform size, are obliquely spherical, and possess distinct radiating ridges, or ribs, which aid the animal in gripping the sand. The mantle has three distinct apertures (inhalant, exhalant, and pedal) through which the inhalant and exhalant siphons and the foot protrude. The cockle lives in sand and mud in shallow water, often in brackish inlets. It burrows until only the siphons project, pulling in water from which the animal strains the minute planktonic organisms on which it feeds. All cockles are hermaphroditic. In order to accomplish the characteristic jumping form of forward locomotion, the large, powerful, muscular foot is bent backward beneath the shell and then straightened. In most adults, the foot is about as long as the greatest length of the shell. Several species of cockles are considered to be good, edible clams. In the British Isles, great numbers of cockles are taken annually for food from densely populated beds. These beds have been known to migrate in units, probably in response to changes in currents. Protothaca staminea, the rock cockle, is among the best known and most widely used for food. It usually does not exceed 3 in. (7.5 cm) in length. Rock cockles are poor diggers and inhabit packed mud, or gravel mixed with sand, usually 8 in. (20 cm) below the surface. They are found on the...