Carcinisation

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."

Carcinisation is believed to have occurred independently in at least five groups of decapod crustaceans, most notably king crabs ,which most scientists believe evolved from hermit crab ancestors (there is still some debate over this point). The other examples are the family Porcellanidae, or porcelain crabs (these are closely related to squat lobsters), the "hairy stone crab", the "coconut crab", and the true crab itself. [cite journal | quotes=no|author = Morrison, C L, A W Harvey, S Lavery, K Tieu, Y Huang & C W Cunningham |year=2001 |title=Mitochondrial gene rearrangements confirm the parallel evolution of the crab-like form |journal=Proc. Roy. Soc. Lond. B |volume=269 |number=1489 |pages=345–350 |url=http://www.biology.duke.edu/cunningham/pdfs/Morrison%2520et%2520al.pdf |doi=10.1098/rspb.2001.1886 |format=Dead link|date=May 2008]

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.

References

*cite journal | quotes=no|author=McLaughlin, P A & R Lemaître |year=1997 |title=Carcinization in the Anomura - fact or fiction. 1. Evidence from adult morphology |journal=Contributions to Zoology |volume=67 |number=2 |pages=79–123 |url=http://dpc.uba.uva.nl/ctz/vol67/nr02/a01
*cite journal | quotes=no|author=McLaughlin, P A, R Lemaître & C C Tudge |year=2004 |title=Carcinization in the Anomura - fact or fiction. 2. Evidence from larval, megalopal and early juvenile morphology |journal=Contributions to Zoology |volume=73 |url=http://dpc.uba.uva.nl/ctz/vol73/nr03/a01