Pertaining to an animal that has a soft body with no bones which is usually covered by a hard shell; as well as some seeds of certain plants: "The bivalvular creatures have two shells and they consume small particles from the water by filtering them."

"Oysters and mussels, permanently attach themselves to hard surfaces as adults and the foot is sedge-shaped and is used for digging in the sand or mud where they secrete tough attachment threads."