Carcinisation

The porcelain crab Neopetrolisthes resembles a crab, but is more closely related to squat lobsters and hermit crabs.

In evolutionary biology, carcinisation (or carcinization) is a hypothesised process whereby a crustacean evolves into a crab-like form from a non-crab-like form. The term was introduced by L. A. Borradaile, who described it as "one of the many attempts of Nature to evolve a crab".^[1]

Carcinisation is believed to have occurred independently in at least five groups of decapod crustaceans, most notably king crabs,^[2][3] which most scientists believe evolved from hermit crab ancestors. The other examples are the family Porcellanidae, or porcelain crabs (which are closely related to squat lobsters),^[4] the hairy stone crab Lomis hirta, the coconut crab Birgus latro, and true crabs.^[5] The example of king crabs (family Lithodidae) evolving from hermit crabs has been particularly well studied and, although some doubt this theory, there is considerable evidence in its favour. For example: most hermit crabs are asymmetrical, so that they fit well into spiral snail shells; the abdomens of king crabs, even though they do not use snail shells for shelter, are also asymmetrical.^[6][7][8][9]

An exceptional form of carcinisation, termed "hypercarcinisation", is seen in the porcelain crab Allopetrolisthes spinifrons.^[10] In addition to the shortened body form, A. spinifrons also shows similar sexual dimorphism to that seen in true crabs, where males have a shorter pleon than females.^[10]

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