Any of more than 20 species (family Trionychidae) of swift-moving, carnivorous turtles found in North American, African, and Asian freshwaters with soft, muddy bottoms. They have a pancakelike, leathery shell; webbed feet; a long neck; and an elongated snout. They often lie buried in mud or sand and occasionally emerge to bask in the sun. Aggressive when captured, they can deliver rapid, vicious bites. The two North American species have a grayish or brown shell, 14-18 in. (35-45 cm) long. Two Old World species grow to 24 in. (60 cm) or more