Any of more than 500 species of decapods that are closely related to the lobster. Nearly all the species live in freshwater, and over half are found in North America. They have a joined head and thorax (midsection) and a segmented body that is yellow, green, red, or dark brown. The head has a sharp snout, and the eyes are on movable stalks. The exoskeleton is thin but tough, and the front pair of legs have large pincers. Crayfish are usually about 3 in. (7.5 cm) long but range from 1 to 16 in. (2.5–40 cm) long.