Ronald Javier, age 8, of Garden Grove, California, for his question:
How does a clam dig himself into the sand?
We must dig down into the sandy silt to find his secret hiding place. So we know that he can dig himself a borrow. But it takes a sharp prong and a pair of strong, grown up hands to open his closed clam shells. You wonder how in the world he used his stiff, solid saucers to dig a hole in the ground.
The soft, juicy clue, lives inside his two sturdy shells. When something scares him, he pulls them shut to protect himself from his hungry enemies. And he holds them shut with two small, but very mighty muscles. He feels scared when someone digs him out of his secret, sandy burrow and bumps him into a basket. When we meet him, he is shut up as tight as a scared clam should be. But he does not spend his everyday life sealed tight in his house of shells. Parts of his soft body are movable and one part can move outdoors.
The clam belongs in the animal class called Pelecypoda. This fancy scientific name means hatchet foot. The clam has one, just one thick, fleshy foot. And when he partly opens his two shells, he can poke this amazing foot outdoors. Sometimes, though not always, it is shaped somewhat like a hatchet. But he never uses it as a hatchet or chopping ax. The muscular foot can move and change its shape. When it takes the shape of a hatchet, it is being used as an anchor or a two sided hook to grip and hold the sand.
When his quiet world is quite peaceful, the clam may rest near the surface. The hinged side of his two shells is uppermost. The partly opened side of his shells is in the moist sand and the crusty clam is half buried. His enemies can spot him and this is not safe. What's more, the food and water he needs are often deeper in the silty sand. So as a rule, he decides to move down lower and to do this, he uses his hatchet foot.
The fleshy foot pokes out from the partly opened shells and stretches downward like a probing finger. Moisture from the clam's juicy body flows down to make the foot swell and grow. It reaches its full length. Then the tip changes its shape and spreads two flat branches, one on each side. The amazing foot now looks somewhat like a hatchet. This is the hatchet shape that the scientists borrowed to name the pelecypoda clam creatures.
When the clam's foot is a pointing finger, it can probe down through the loose, moist sand. But when the tip changes to a flat ax, it can probe no farther. However, this hatchet can grip and grab like the hooks of an anchor. And this is dust what it does. While the hatchet holds tight into the sand, the rest of the foot begins to pull itself shorter. And as it does so, it pulls the solid clam with it, sliding down through the soft, silty sand. Now it is time for the foot to pull in its hatchet and change back again to a probing finger. Once again, the hatchet grows and grips while the clam is pulled another and then another notch deeper into the sand.
Now you know how a clam digs himself into the sand. But chances are, you cannot guess which is his front end or which side is which. His front, strange to say, is at the hinged side of his shells. And, of all things, his two sturdy shells are cupped one on each of his sides. Actually, the proper position for the little double saucer is not flat, but standing upright on one edge with the hinged edge of his shells at the top.