The genus Andrias contains the largest living salamanders, and fossil species attained even larger sizes, exceeding 2 meters in body length. Fleshy dermal folds are visible along the lower sides of the body in adults. Cryptobranchids are generally found living in depressions under stones in streams and rivers. Andrias occurs in central China and Japan, whereas Cryptobranchus lives in eastern North America. Mating in Cryptobranchus occurs in late summer or early fall.
Males prepare nests below large, submerged stones or logs.
Females lay long, paired strings of several hundred eggs which are fertilized externally by the male. Males guard the eggs until they hatch in 2-3 months after laying. Fossils indicate that Cryptobranchus formerly occurred also in western North America. Asian salamanders of the genus Andrias are used for food and are now considered highly endangered. These large, aquatic salamanders have dorsoventrally flattened bodies except on the tail, which is laterally compressed and finlike.