The hellbender is the second largest salamander species in the world. The length is 12 inches to 29 inches, and it resembles an eel, with a broad, flattened head and body. The female is larger than the male. The coloration is gray to olive-brown on the upper sides and back, with variable amounts of spotting or dark mottling. A wrinkled, fleshy fold of skin is present along each side of the body (this wrinkled skin increases surface area for oxygen absorption). On the neck there is a single pair of circular gill openings. The rear half of the body is ridged. The eyes are beady and inconspicuous. The legs are tucked under the body.