hermit crab

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hermit crab,

a crustaceancrustacean
, primarily aquatic arthropod of the subphylum Crustacea. Most of the 44,000 crustacean species are marine, but there are many freshwater forms. The few groups that inhabit terrestrial areas have not been particularly successful in an evolutionary sense; most require
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 distinguished from true crabs by its long, soft, spirally coiled abdomen terminating in an asymmetrically hooked tail. Most hermit crabs protect this vulnerable portion of their bodies by occupying the empty shells of periwinkles, whelks, and other gastropod mollusks. A few find other homes; for example, a species that inhabits the Indian Ocean lives in sections of old bamboo cane. When the hermit crab grows out of one shell it seeks a larger one, fighting for it if challenged. Sea anemones often attach themselves to these shells, obtaining free transportation and scraps of food in return for protecting their hosts. Hermit crabs are common beach scavengers in most parts of the world.

Most species are marine, but some tropical forms, such as the coconut, or robber, crab, Birgus latro, are largely terrestrial. This species, the largest hermit crab, generally reaches over 1 ft (30 cm) in length. It becomes increasingly terrestrial and develops heavy armor as it matures into an adult, at which stage it is able to completely discard its adopted shell. With its great pincers it has been known to crack coconuts, which it obtains by climbing palm trees.

Hermit crabs are classified in the phylum ArthropodaArthropoda
[Gr.,=jointed feet], largest and most diverse animal phylum. The arthropods include crustaceans, insects, centipedes, millipedes, spiders, scorpions, and the extinct trilobites.
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, subphylum Crustacea, order Decapoda.

hermit crab

[′hər·mət ‚krab]
(invertebrate zoology)
The common name for a number of marine decapod crustaceans of the families Paguridae and Parapaguridae; all lack right-sided appendages and have a large, soft, coiled abdomen.

hermit crab

any small soft-bodied decapod crustacean of the genus Pagurus and related genera, living in and carrying about the empty shells of whelks or similar molluscs