Dimyoidea

Dimyidae is a family of extremely flattened, small (<1 cm), pleurothetic, relatively rare marine bivalve molluscs in the order Pectinida inhabiting the deeper regions of continental shelves from the Caribbean to Japan. They are sometimes called dimyarian oysters. Unlike other ostreids, the dimyarian oysters attach themselves to a substrate via their right (rather than left) valves. They are related to the scallops and other oysters.