The Spot-Bellied Side-Necked Turtle is the largest member of the Phrynops genus, growing up to 18 inches in length. The carapace is olive-brown with yellow margins, and is parallel sided with a flattened top. The plastron is yellow with symetrically-placed round black spots. The distinctive feature is a narrow black line running along each side of the neck through the eyes and snout. Above this line the color is gray, and below it is white. Also, two barbels ringed at the base project downward from the underside of the head.