Crab | 水產百科網

CrabsaredecapodcrustaceansoftheinfraorderBrachyura,whichtypicallyhaveaveryshort...Femalescanstorethespermforalongtimebeforeusingittofertilisetheireggs.Whenfertilisationhastaken...Afteronemoremoult,thecrabisajuve

Infraorder of decapod crustaceans

Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) (Greek: βραχύς, romanized: brachys = short,[2] οὐρά / οura = tail[3]), usually hidden entirely under the thorax. They live in all the worlds oceans, in fresh water, and on land, are generally covered with a thick exoskeleton, and have a single pair of pincers. They first appeared during the Jurassic Period.

Crabs are generally covered with a thick exoskeleton, composed primarily of highly mineralized chitin,[4][5] and armed with a pair of chelae (claws). Crabs vary in size from the pea crab, a few millimeters wide, to the Japanese spider crab, with a leg span up to 4 m (13 ft).[6] Several other groups of crustaceans with similar appearances – such as king crabs ...