Silvery to brownish grey in colour. Body short and tall, flattened like a disc. Ventral fins absent. Caudal fin replaced by a stiff fringe of skin. Dorsal and anal fins modified to form long 'paddles' that can only move from side to side. Skin leathery without scales. Small eyes and mouth. May grow up to 4 m in length and 2 tonnes in weight.Often seen drifting at the surface while on its side or close to the surface with its dorsal fin projecting out of the water. Feeds on zooplankton, jellyfish, eel larvae and small deep sea fish.