Tail is vertically compressed with prominent dorsal and ventral fins. Each side of trunk and posterior margins of legs with wrinkled, fleshy folds of skin. Ground color usually gray, but varying from yellowish brown to almost black. Irregular dark blotches on dorsum and sides. No external gills.
Gill slits present, but difficult to detect.
Front feet with four toes and hind feet with five toes. Similar species include mudpuppies and waterdogs, but both have external gills and four toes on the hind feet. Adults lack eyelids and retain one pair of gill slits. Hellbenders also express unusual specializations associated with cutaneous respiration. Fleshy folds along the body and legs increase the surface area of the skin available for gas exchange.