While it appears stuffed with bread crumbs and spinach upon the table, the crab appears quite different in the ocean. A most delicious meal, the clam is a burrower and lives deep within the sand. It is a small sessile creature and a filter feeder via its incurrent and excurrent siphons. The hinge ligament opens and closes the shell. The oyster and scallop are also members of the phylum Mollusca and the class Bivalva.
Oysters are prized possessions because they have the ability to form pearls.
Years later, after many layers of calcium carbonate have been secreted, a pearl emerges. Scallops are very interesting creatures. They inhabit the grassy beds found along the seafloor, and they swim by moving water in and out of their valves. A stream of water shoots out at the hinge and moves the scallop backward. The octopus does not have an external shell.