Any of more than 400 species (family Pectinidae) of marine bivalves found worldwide, from the intertidal zone to deep waters. The two halves of the shell (valves) are usually fan-shaped, except for a winglike projection at either side of the straight hinge. The shells are 1–6 in. (2.5–15 cm) long. They may be smooth or ribbed and red, purple, orange, yellow, or white. Cilia filter microscopic plants and animals from the water and move them toward the mouth. Scallops swim by clapping the valves, propelling themselves forward. The muscle that closes the valves is a popular food item.