In most clams, two adductor muscles contract to close the shells. The clam has no head, and usually has no eyes, (scallops are a notable exception), but a clam does have kidneys, a heart, a mouth, and an anus. A clam does not have any of the five senses so they cannot smell, taste, feel, hear or see. The shell has 3 layers. The top one is called mother-of-pearl because it is a coating of pearl material. Clams have a burrowing foot that they use to dig down into the sand or mud to hide. If you go to the beach and see little holes that appear in the sand each times the waves go away, it is probable that clams made them. Scientists classify clams by how far down they dig and what kind of surface they dig into. Some burrow less than an inch under the sand, while others dig several inches below the surface.