A marine bivalve mollusc (superfamily Pectinoidea) that in most cases is free-living and capable of swimming by rapidly opening and closing its valves to escape from predators such as starfish. Scallops have up to 100 simple eyes around the edges of their shells. Most scallops live on sandy seabeds, although a few species cement themselves to rocks. There are probably more than 30 genera with 350 species found in all oceans. Many are caught for food.