Joyce Perry, age 10; of San Diego, Calif., for her question:
How does a clam bury himself?
The clam has one foot. It takes him wherever he wants to go ‑ which is not very far or very fast. It can take him through the sand or mud or help him to bury himself under the surface. This foot is a band of tough muscle, which the clam can poke out of his shell as he needs it.
The clam is a bivalve animal, cousin to the oyster. The bivalve name refers to his two shells. As anybody who has tried to open those two sheds knows they are held together by a very strong pair of muscles. Mr. Clam can close his doors and keep them closed against most of his enemies.
The oysters of course, cannot move from place to place. He settles on a solid spot for life and lets the sea bring him his food and oxygen. The clam likes to move about, within reason. And for this he uses his one clam foot. This lump of muscle can be drawn into the shell behind closed doors, or it can be sent outside the shell and controlled from muscles inside.
The foot movement is more or less the same whether the clam is burrowing into the mud or going for a stroll. The band of foot muscle pokes out like a pointed tongue. The tip of the foot swells up and acts as an anchor. An extra flow of blood into a cavity in the toe makes this possible. The anchor tip grips the soil when it is spread wide like a little spade.
The muscles behind the tip now go into action. They contract or shrink. The tip of the foot remains anchored ‑ but something must move when these muscles contract. The clam moves. The whole bulky body is inched along towards the anchored toe of the foot.
The anchor then lets go. The foot shrinks to normal size and extends itself as a pointing toe. It finds another spot of earth into which it can anchor and the process repeats itself. Bit by bit the clam inches himself along on his one foot. Or bit by bit he inches himself down until he is buried in the mud or sand, buried clam, of course, needs his food and water. To take care of these problems he has a long neck which. reaches up through the mud or sand to the surface, There is a siphon tube in this neck through which water passes up and dawn. About three quarts of water piss through the clams body every hour. Instead of lungs, the clam has gills far taking oxygen from water. The water in which he lives is never clean and pure. In fact, if it were the poor follow would soon starve.
The river water or sea water in which the clam lives is filled with little bits of this end that. There are tiny algae plants And broken bits of decaying seaweed. These provide the salads and vegetables on the little fellow's diet. There are bits of decaying fish, little bacteria and midget fish eggs. So the clam has a balanced diet of meat and vegetables. This seafood salad is floated into his stomach on the water. And, when the diet does not suit him, Mr. Clam can always put out his little foot and stroll along to greener pastures.