Large (up to 49 cm CL), aggressive, aquatic turtle with a relatively unpatterned carapace in cryptic shades of brown, olive, gray, or black. Head moderately large, beak moderately hooked, two chin barbels. Liberal covering of tubercles on back of neck. Plastron much reduced, cross-shaped, offering little protection. Legs muscular, feet broad with long claws and extensive webbing between toes. Male grows larger, has thicker tail base, and vent opening behind edge of carapace.