Like oysters (family Ostreidae), scallops have a central adductor muscle, and thus the inside of their shells has a characteristic central scar, marking the point of attachment for this muscle. The adductor muscle of scallops is larger and more developed than that of oysters, because they are active swimmers; scallops are in fact the only migratory bivalve. The adductor mussel quickly opens and closes the shell, expelling water, which allows the scallop to move. This method of motion is also a defensive technique, protecting it from threatening predators.
Scallops possess eyes with a lens and retina, which are more complex compared to other bivalves. Their eyes can't see shapes, but can detect light and motion.