what is the evolution of the just mentioned type of crab?
They are an example of carcinisation, whereby a noncrab-like animal (in this case a relative of a squat lobster) evolves into an animal that resembles a true crab.
Porcelain crab
 are an example of carcinisation, whereby a noncrab-like animal (in this case a relative of a squat lobster) evolves into an animal that resembles a true crab. 
what is coconut crab? It is a species of terrestrial hermit crab, also known as the robber crab or palm thief. It is the largest land-living arthropod in the world what are the classification of the above mentioned species of crab? Squat lobsters and porcelain crabs describe the former mentioned Squat lobsters are dorsoventrally flattened crustaceans with long tails held curled beneath the cephalothorax. how are these classified? Squat lobsters were placed together in the superfamily Galatheoidea alongside the porcelain crabs of the family Porcellanidae.
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Porcelain crab [SEP] Evolution
Porcelain crabs are an example of carcinisation, whereby a noncrab-like animal (in this case a relative of a squat lobster) evolves into an animal that resembles a true crab. Porcelain crabs can be distinguished from true crabs by the apparent number of walking legs (three instead of four pairs; the fourth pair is reduced and held against the carapace), and the long antennae originating on the front outside of the eyestalks. The abdomen of the porcelain crab is long and folded underneath it, free to move.