Bivalve Anatomy: Clams, Scallops & Oysters Explained
Bivalve Anatomy
Clams
Clams, such as the northern quahog, are bivalves, meaning they have two hinged shells. These shells are closed by adductor muscles, which can be relaxed to allow the shell to open via ligaments near the umbo (the hinge area). The clam uses its foot to burrow into the sand, while long siphons extend from its mantle to filter water. Water and food particles enter one siphon, pass through the gills (where tiny cilia trap food in mucus), and are then guided to the clam's mouth by palps. The second siphon expels the filtered water. The clam’s mantle secretes its shell, with the umbo being the oldest part, from which the shell grows.
Scallops
Scallops, like the Atlantic bay scallop, do not burrow but instead move by rapidly opening and closing their valves using the adductor muscle, which ejects water and propels them. Scallops have blue eyes along the edge of their mantle that detect movement, particularly to warn against predators like sea stars. The adductor muscle, which is commonly eaten, is just one of the edible parts of the scallop.
Oysters
Oyster larvae, such as the eastern oyster, attach their mantles to rocks, shells, or other solid surfaces and filter algae from the water as they grow. Oysters are protandric, meaning they begin life as males and typically become females as they age. The shape of an oyster's shell is influenced by the density of the bed they are part of, with crowded oysters often developing differently than those with more space.