Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit crab, most of which possess an asymmetric abdomen concealed by a snug-fitting shell. Hermit crabs' soft (non-calcified) abdominal exoskeleton means they must occupy shelter produced by other organisms or risk being defenseless.
Carcinisation is a form of convergent evolution in which non-crab crustaceans evolve a crab-like body plan. The term was introduced into evolutionary biology by L. A. Borradaile, who described it as "the many attempts of Nature to evolve a crab".
The Coenobitidae are the family of terrestrial hermit crabs, widely known for their land-living habits as adults. They are found in coastal tropical regions around the world and require access to the ocean to breed.
The genus Coenobita contains 17 species of terrestrial hermit crabs. Several species in this genus are kept as pets.
The Diogenidae are a family of hermit crabs, sometimes known as "left-handed hermit crabs" because in contrast to most other hermit crabs, its left chela (claw) is enlarged instead of the right. It comprises 429 extant species, and a further 46 extinct species, making it the second-largest family of marine hermit crabs, after the Paguridae.
The Paguridae are a family of hermit crabs of the order Decapoda. The king crabs, Lithodoidea, are now widely understood to be derived from deep within the Paguridae, with some authors placing their ancestors within the genus Pagurus.
The Pylochelidae are a family of hermit crabs. Its members are commonly called the 'symmetrical hermit crabs'. They live in all the world's oceans, except the Arctic and the Antarctic, at depths of 2,000 m (6,600 ft). Due to their cryptic nature and relative scarcity, only around 60 specimens had been collected before 1987, when a monograph was published detailing a further 400.
Dardanus megistos, the white-spotted hermit crab or spotted hermit crab, is a species of hermit crab belonging to the family Diogenidae.
Clibanarius fonticola is a species of hermit crab from Vanuatu. It lives exclusively in fresh water, the only hermit crab in the world to do so. While a number of other hermit crabs are terrestrial or live in estuarine habitats, and certain brackish water species can tolerate low salinity levels for a time, no other hermit crab spends its entire life in fresh water; the only other fully freshwater anomurans are the South American aeglids.
Pagurus sinuatus is a large species of hermit crab found in Australia and the Kermadec Islands. It is red or orange in colour with coloured bands on the legs and patches on the body.
Ciliopagurus liui is a species of hermit crab native to the Gulf of Tonkin and waters to the south of Japan.
The Pylojacquesidae are a small family of hermit crabs, comprising only two monotypic genera. The family was erected in 2001, after two specimens at Museum für Naturkunde at the Humboldt University of Berlin were recognised as being quite distinct from other described hermit crabs. The family members differ from other hermit crabs in that their mandibles are chitinous and toothed.
Pagurus samuelis, the blueband hermit crab, is a species of hermit crab from the west coast of North America, and the most common hermit crab in California. It is a small species, with distinctive blue bands on its legs. It prefers to live in the shell of the black turban snail, and is a nocturnal scavenger of algae and carrion.
Calcinus tubularis is a species of hermit crab. It is found in the Mediterranean Sea and around islands in the Atlantic Ocean, where it lives below the intertidal zone. Its carapace, eyestalks and claws are marked with numerous red spots. C. tubularis and its sister species, C. verrilli, are the only hermit crabs known to show sexual dimorphism in shell choice, with males using normal marine gastropod shells, while females use shells of gastropods in the family Vermetidae, which are attached to rocks or other hard substrates.
Porcellanopagurus edwardsi is a species of hermit crab that lives in the waters around New Zealand and its subantarctic islands.
Dardanus venosus, the starry-eyed crab or stareye crab, is a species of hermit crab in the family Diogenidae. It occurs in shallow water on the eastern coasts of America from Florida southward to Brazil. It is sometimes kept in reef aquaria.
The thinstripe hermit crab, Clibanarius vittatus, is a species of hermit crab in the family Diogenidae. It is found in the Caribbean Sea, the Gulf of Mexico and the western Atlantic Ocean.
Coenobita scaevola is a species of terrestrial hermit crab from the western Indian Ocean and Red Sea.
Aniculus maximus, the hairy yellow hermit crab or large hairy hermit crab, is an aquatic hermit crab of the family Diogenidae.
Labidochirus splendescens, commonly known as the splendid hermit crab, is a species of hermit crab found in the northeastern Pacific Ocean off the coast of North America. It is more heavily calcified and inhabits smaller mollusc shells than most hermit crabs.
