Kathy Guyader, age 10, of Milltown, New Jersey, for her question:
What exactly is a horseshoe crab?
Most animal families gradually change through millions of years. But not all of them. The stodgy turtles have not altered much through the ages and the ancestors of crocodiles shared the world with the dinosaurs. The strange horseshoe crab is more living proof that it's not al_i ;ays best to change with the times. And he has been proving this much lower than the turtles and crocodiles.
He belongs to the huge arthropod group of animals which includes the shrimps and insects, the crabs red spiders. But the horseshoe crab, alias the king crab, is not really a true crLb. In spite of his somewhat crabby appearance, he is more closely related to the spiders. Scientists classify him and his four cousins in a special class all their o rn. He is called the horseshoe crab because his shell is shaped like the outline of a horse's hoof. This hard shell humps over his entire body, with its eig?it crabby legs, and tapers back to end in a long pointed tail. He is called the king crab because of his size. When grown he may be one foot wide and two feat long.
His home is the sea nn,! we find him along the Atlantic shores of North and South America.. He has relatives living off Japan and other shores of the Pacific. While he searches for food on the bed of the sea, he depends on his tough, crusty armor to protect him from his foe. As a rule, it does. But sometimes when grubbing for a maal, he gets a claw caught between the shells of a clam. Otherwise, as a grown up king crab he is fairly safe. But his earlier life is very, very risky.
Life begins in early spring, when the adults leave the deep water and crowd in to the shallows near the shores. The females dig hollows in the sand, just about where the lcw tide ebbs from the beaches. Then they coax the males to strew their milt over the nests to fertilize the little green eggs. Sometimes the females grab the males in groups and pull them to the shore. The parents then go back to grubbing on the ocean floor. In time, the eggs turn clear and the tiny embryos can be seen curled up inside. They hatch in three to ten weeks, depending on the warmth of their watery world. Right away, they troop down to deeper water.
A row of 20 of them measures about an inch. They have no tails and are not much like their horseshoe shaped parents. Scientists say that the crawly little fellows look like their ancient ancestors, the trilobites. Many of them are smashed by the pounding sea and many more are devoured by fish and other hungry foes. The few survivors eat and grow. As their shells become too tight, the young crabs molt, shedding them for bigger ones. In the first year, they molt several times and grow 1 1/2 inches long. They also grow tails. In about four years, they become fully mature, although some king crabs keep growing and molting for eight years or more.
Scientists suspect that horseshoe crabs thrived in the seas of 300 million years ago. They were there when the first insects set up housekeeping on the land. About 200 million years ago, they may have seen the first salamanders and then the first reptiles leave the seas. They lived through the long age of the dinosaurs and on into the age of mammals. And through all these ages, the horseshoe crabs have refused to change with the times.