Carcinisation is a hypothesised process whereby a crustacean evolves into a crab-like form from a non-crab-like form. The term was introduced by Borradaile, who described it as "one of the many attempts of Nature to evolve a crab". Classes & Subclasses Branchiopoda Phyllopoda Sarsostraca Remipedia Cephalocarida Maxillopoda Thecostraca Tantulocarida Branchiura Pentastomida Mystacocarida Copepoda Ostracoda Myodocopa Podocopa Malacostraca Phyllocarida Hoplocarida Eumalacostraca The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum [1]. They include organisms such as lobsters, crabs, shrimp and barnacles. ... A hypothetical phylogenetic tree of all extant organisms, based on 16S rRNA gene sequence data, showing the evolutionary history of the three domains of life, bacteria, archaea and eukaryotes. ... Supfamilies See text Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short tail (Greek: brachy = short, ura = tail), or where the abdomen is entirely hidden under the thorax. ... The deepest visible-light image of the universe, the Hubble Ultra Deep Field. ...

Carcinisation is believed to have occurred in at least five groups of decapod crustaceans, independently, 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, Lomis, Birgus latro, and the Brachyura itself (true crabs) ^[1]. Suborders and Infraorders Dendrobranchiata Pleocyemata Caridea Stenopodidea Reptantia, comprising: Eryonoidea Achelata Astacidea Glypheidea Thalassinidea Anomala Brachyura The decapods or Decapoda are a group of crustaceans within the class Malacostraca, including many familiar groups of crustaceans, such as crabs, lobsters and shrimp, but also some families that are less well known. ... Genera Acantholithodes Cryptolithodes Dermaturus Glyptolithodes Hapalogaster Lithodes Lopholithodes Neolithodes Oedignathus Paralithodes Paralomis Phyllolithodes Placetron Rhinolithodes King crabs, also called stone crabs, are a family of crab-like decapod crustaceans chiefly found in cold seas. ... Hermit crabs are decapod crustaceans of the infra-order Paguroidea, distinct from the true crabs in the infra-order Brachyura. ... Genera Aliaporcellana Capilliporcellana Clastotoechus Euceramus Enosteoides Eulenaios Lissoporcellana Megalobrachuium Minyocerus Neopetrolisthes Neopisoma Pachycheles Parapetrolisthes Petrolisthes Pisidia Polyonyx Porcellana Porcellanella Pseudoporcellanella Raphidopus Ulloaia Porcelain crabs are decapod crustaceans in the family Porcellanidae, which superficially resemble true crabs. ... Families and genera Chirostylidae Ortmann, 1892 Chirostylus Ortmann, 1892 Eumunida Smith, 1883 Gastroptychus Caurelly, 1896 Pseudomunida Uroptychus Baba, 1988. ... Binomial name Birgus latro Linnaeus, 1767 The Coconut crab (Birgus latro) is the largest terrestrial arthropod, known for its ability to crack coconuts with its strong pincers in order to eat the contents. ... Sections Dromiacea Raninoida Heterotremata Thoracotremata The term crab is sometimes applied to several different groups of short (nose to tail) decapods with thick exoskeletons, but only members of the Brachyura are true crabs; other taxa, such as hermit crabs, porcelain crabs, king crabs, and horseshoe crabs are, despite superficial similarities...

The example of king crabs (family Lithodidae) evolving from hermit crabs has been particularly well studied and, although some workers 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. Square with symmetry group D4 Symmetry is a characteristic of geometrical shapes, equations, and other objects; we say that such an object is symmetric with respect to a given operation if this operation, when applied to the object, does not appear to change it. ... The name snail applies to most members of the molluscan class Gastropoda that have coiled shells. ... Various seashells The hard, rigid outer covering of certain animals is called a shell. ... The abdomen (from the Latin word meaning belly) is the part of the body between the pelvis and the thorax. ...

References

• McLaughlin, P A & R Lemaître (1997). Carcinization in the Anomura - fact or fiction. 1. Evidence from adult morphology. Contributions to Zoology 67: 79–123.
• McLaughlin, P A, R Lemaître & C C Tudge (2004). Carcinization in the Anomura - fact or fiction. 2. Evidence from larval, megalopal and early juvenile morphology. Contributions to Zoology 73.

1. ^ Morrison, C L, A W Harvey, S Lavery, K Tieu, Y Huang & C W Cunningham (2001). Mitochondrial gene rearrangements confirm the parallel evolution of the crab-like form. Proc. Roy. Soc. Lond. B 269: 345–350.