Don Dawson, Age 12, of Costa Mesa, Calif., for his question:
How does a crab shed his shell?
Mr. Crab is never a sweet natured animal. But at molting time, he is even mare crabby than usual.. No one could blame him for this, because for a few days the poor fellow is at the mercy of his many foes. He is a soft shelled crab, trying to keep out of sight, and Very annoyed if anyone disturbs his privacy.
A newly hatched crab must go through a Series of molts before he begins to look like his parents. At last he becomes a miniature crab, but for the rest of his life he will molt his shell from time to time. His crusty shell has many advantages. But molting time is very risky and uncomfortable for the crab. And this may happen more than once during the year.
Just before shedding time, the body of the crab withdraws some of the salty minerals in the old shell. Under the shell, he grows a tough skin, 8 leathery copy of his existing, crusty shell. The humped shell over the crab's back is called the carapace, and when all is ready for molting, a crack appears in the carapace. The escape hatch opens near the rear of the carapace in a straight line from side to side.
Mr. Crab struggles and struggles to free himself. At last he steps forth and leaves his crusty old shell behind him. He is now clothed in a pliable coat, too thin to protect him from his toothy enemies. He is a soft shelled crab, and the helpless fello4r scuttles away to hide himself.
The crab's body immediately becomes enlarged with extra liquids. The pliable new shell is pushed out and extended to the limit. In a few days, it begins to harden with deposits of limy minerals. Soon it is as crusty as the old shell left behind. Mr. Crab comes forth again to fight his endless battles with the hungry sea.
The crab has no bony skeleton inside his body. His shell is an exoskeleton which serves to support his internal organs and shelter him from attack. But the encasing shell cannot stretch to keep pace with the crab as he grows. After a molt, the new shell is a little roomier. What's more, the old shell may be cracked or worn or even cluttered with barnacles, so the new shell gives the crab a new lease on life.
There are 1000 or more species of crab, and most of them are smaller than half an inch. A giant king crab has a carapace 18 inches long and afoot wide. His stringy legs may stretch to a width Of 10 feet or more. All crabs belong in the class Crustacea, meaning the crusty animals. The lobsters, shrimps and crayfish are also crustaceans. They, too, molt and shed their crusty coats from time to time.