Visceral mass twists 180 degrees, with U- shaped digestive system. Anus above head. May let head enter shell first, rather than foot. Elastic ligaments open shell, adductor muscles close the shell. Shell is calcium carbonate, secreted by mantle.
Mother of pearl is the inner layer of shell.
A particle of sand gets stuck between shell and mantle, concentric layers of calcium carbonate secreted from mantle to form pearl. Real pearls have rough surface. Along edge of scallop shell, they can detect image. Oysters attach permanently, clams burrow, as do shipworms. Scallops swim by clapping their shells together.