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. Clams, oysters are suspension feeders.
Water comes in by incurrent siphon, moves over gills.
Gills are covered with mucus that traps bits of food. Food is moved by cilia to mouth. Most have 2 separate sexes, with sperm shed into water, enters female and fertilizes eggs in mantle cavity. Young develop in female. Tentacles have suckers to hold prey.