HERMIT CRAB

any crab of the families Paguridae and Coenobitidae (order Decapoda of the subclass Crustacea). The crabs use empty snail shells (e.g., whelk or periwinkle) or other hollow objects as a shelter for partial containment and protection of the body. Hermit crabs, worldwide in distribution, occur in sandy- or muddy-bottomed waters and occasionally on land and in trees. The soft abdomen is asymmetrical, usually curling to the right. There are two pairs of antennae and four pairs of legs. The first pair of legs is modified to form chelae, or pincers-the right one usually larger-that are shaped so as to cover the shell entrance when the animal is inside. The crab walks on its second and third pairs of legs and uses its last pair, on the end of the abdomen, to grip the central column of the shell. Abdominal appendages in the female carry the eggs, which are held there until they hatch; the young immediately pass into the water and search for their own shells. As the crab grows, it periodically leaves its shell and finds and moves into a larger one. Some hermit crabs live in the tubes of plant stems. Semiterrestrial, tropical species of Coenobita inhabit sections of bamboo stems, broken coconut shells, and other articles, in addition to seashells. Pylocheles, a deepwater crab of the Indian Ocean, lives in bamboo sections; Xylopargus, found in West Indian waters at depths of 180 to 360 m (600 to 1,200 feet), lives in hollow cylinders of wood. Other species make homes in coral or sponge. Some species live in close association with other animals. Pagurus (Eupagurus) bernhardus, a common, bright red hermit crab of European and North American coastal waters, often carries one or more anemones on its shell. The robber crab (q.v.), native to islands of the South Pacific, is a terrestrial species that has discarded the shell-dwelling habit. Pagurus pollicaris, the so-called large hermit crab of the Atlantic coastal waters of North America, is reddish brown and about 10 to 12 cm (4 to 5 inches) long. P. longicarpus, the small hermit crab, occurs in U.S. Atlantic coastal waters and has cylindrical pincers.