scallop or pecten, marine bivalve mollusk. Like its close relative the oyster, the scallop has no siphons, the mantle being completely open, but it differs from other mollusks in that both mantle edges have a row of steely blue "eyes" and tactile projections. The rounded shells have radiating ribs with flared "ears" or "wings" at the hinge. Scallops are capable of swimming or leaping about by snapping their shells, which are controlled by a powerful adductor muscle, the only part of the animal that is eaten. Scallops are more common on the Atlantic coast than the Pacific. The common scallop is about 2 in. (5 cm) long. Found abundantly in shallow and offshore waters and in eelgrass and mud flats from Cape Cod to Texas, it is taken in large numbers around Long Island. The giant scallop, found in deeper waters from Labrador to New Jersey, attains a length of 5 in. (12.7 cm). Scallops are classified in the phylum Mollusca, class Pelecypoda or Bivalvia, order Filibranchia, family Pectinidae.