Scallops and clams are often confused due to their shared bivalve classification and similar marine habitats. While both are mollusks, distinct biological characteristics set them apart.
What Defines a Scallop?
Scallops are marine bivalve mollusks known for their fan-shaped shells with radial ribs and small “ears” near the hinge. The most commonly consumed part of a scallop is its large, cylindrical adductor muscle, which is responsible for opening and closing its shells. This powerful muscle enables many scallop species to move through water using a form of jet propulsion. They do this by rapidly clapping their shells together, expelling water and propelling themselves. Unlike many other bivalves, most adult scallops are free-living and often rest on the seabed surface rather than being buried. They possess numerous eyes, up to 200, appearing as small blue dots along their mantle, which detect light and movement. Scallops belong to the taxonomic family Pectinidae, with over 300 species found worldwide.
What Defines a Clam?
Clams are also bivalve mollusks, but their shells generally exhibit a more rounded or oval shape compared to scallops, often appearing smoother and thicker. Their shells frequently display concentric growth rings, which are similar to tree rings and indicate their age. Most clams are infaunal, meaning they live buried within the sand or mud of the seafloor or riverbeds. They use a strong, muscular foot to dig and burrow into the substrate, allowing them to anchor themselves in place. For feeding and respiration while buried, clams extend tube-like structures called siphons up into the water column. One siphon draws in water containing food particles and oxygen, while the other expels filtered water and waste. This sedentary, buried lifestyle contrasts with the more mobile nature of scallops. Clams encompass a diverse group of species, belonging to various families within the order Veneroida.
Distinguishing Scallops from Clams
While both are bivalve mollusks with two hinged shells, scallops and clams have distinct characteristics. Taxonomically, scallops are members of the family Pectinidae within the order Pectinida, while clams belong to various families primarily within the order Veneroida.
Differences in shell appearance are readily apparent; scallops have a fan-like shell with radial ribs and distinctive “ears” near the hinge, whereas clam shells are typically more rounded or oval and smoother. Their modes of movement and preferred habitats also vary significantly.
Scallops are unique among bivalves for their ability to “swim” using jet propulsion, allowing them to escape predators and move across the seabed. In contrast, clams are largely sedentary and burrow into soft substrates, extending only their siphons to the water.
The edible parts of these mollusks further distinguish them. When consuming scallops, one primarily eats the large, tender adductor muscle responsible for their swimming motion. For clams, the entire soft body, including the foot, mantle, and siphons, is typically consumed, resulting in a chewier texture.
Furthermore, scallops possess a sophisticated visual system with up to 200 blue eyes lining their mantle, enabling them to detect movement and light. Clams, due to their buried lifestyle, generally have less developed sensory organs. Despite these distinctions, both are marine filter feeders, contributing to water clarity by straining particles from their environment.