hermit crab

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of various crabs belonging to a group within the order Decapoda that protect their soft unarmored abdomens by occupying and carrying about the empty shells of snails or other univalve mollusks.

Century Dictionary and Cyclopedia

1. n. A crab of the family Paguridæ (which see). This crab has neither a long hard tail like a shrimp or crawfish, nor yet a short one doubled underneath like ordinary crabs, but a soft fleshy one requiring to be covered and protected. To this end it takes possession of and occupies a cast-off shell of some univalve mollusk, such as a periwinkle or a small whelk. The crab backs into the shell, inserting the tender abdomen in the spire, and filling the aperture of the shell with his claws and other hard parts, thus guarding his otherwise unprotected and vulnerable rear. In moving about, the crab carries his house with him, like a snail with his shell on his back, and quits it for another only when he outgrows it. In many cases sea-anemones grow on the shell, the triple association furnishing an excellent example of commensalism. (See cut under cancrisocial.) There are several genera and numerous species of hermitcrabs; the commonest belong to Pagurus and Eupagurus. (See cut under Eupagurus.) The Diogenes crab, a species of Cenobita, belongs here. The most common hermit-crab on the Atlantic coast of the United States is the short-armed hermit, Eupagurus pollicaris, attaining a large size and inhabiting the shells of such mollusks as Pyrula and Natica. It is called by the fishermen jack-in-the-box, thief, and stone-lobster, and is believed by some to turn into a lobster.

Wiktionary

1. n. A type of crab species which salvages empty seashells or other portable objects to permanently shelter and protect their soft abdomens.

GNU Webster's 1913

1. n. (Zoöl.) a marine decapod crustacean of the family Paguridæ. The species are numerous, and belong to many genera. Called also soldier crab. The hermit crabs usually occupy the dead shells of various univalve mollusks. See Illust. of Commensal.

WordNet 3.0

1. n. small soft-bodied marine crustaceans living in cast-off shells of gastropods