crab 的英文资料

Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (Greek: βραχύ/brachy = short, ουρά/οura = tail), or where the reduced abdomen is entirely hidden under the thorax. They are generally covered with a thick exoskeleton, and armed with a single pair of chelae (claws). 6,793 species are known.[1] Crabs are found in all of the world's oceans. Additionally, there are also many freshwater and terrestrial crabs, particularly in tropical regions. Crabs vary in size from the pea crab, only a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 m.[2]

The infraorder Brachyura contains about 93 families [3], as many as the remainder of the Decapoda.[4] The evolution of crabs is characterised by an increasing robustness of the body, and a reduction in the abdomen. Although many other groups have also undergone similar processes of carcinisation, it is most advanced in crabs. Th