The mantle, which secretes the shell, is the dorsal body wall covering the visceral mass.The mantle cavity is lateral and in most bivalves, the gills have a respiratory and digestive function.

• 双壳贝的外壳是由外套膜分泌而来；套膜包覆著内脏；在多数双壳贝中；外套腔多位于两侧；鳃具有呼吸和消化的功能.