crayfish, also called
crawfish or
crawdad, any of numerous crustaceans (order Decapoda, lum Arthropoda) constituting the families Astacidae (Northern Hemisre), Parastacidae, and Austroastracidae (Southern Hemisre). They are closely related to the lobster. Over half of the more than 500 species occur in North America. Nearly all live in fresh water, although a few species occur in
brackish water or salt water.
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Crayfish are characterized by a joined head and thorax, or midsection, and a segmented body, which is sandy yellow, green, red, or dark brown in colour. The head has a sharp snout, and the compound eyes are on movable stalks. The exoskeleton, or body covering, is thin but tough. The front pair of the five pairs of legs have large, powerful pincers (chelae). There are five pairs of smaller appendages on the abdomen, used mostly for swimming and circulating water for respiration.