Chiefly marine; also in brackish and freshwater. Atlantic, Indian and Pacific Oceans. Side of head continuous with the anterior margin of pectoral fin. Dorsal fin totally absent or indistinct, when present. Disc about 1.2 times as broad as long. No caudal fin. Tail long and whip-like. Most species with at least 1 long venomous spine on tail, which can cause excruciating pain to humans. Largest species to about 4 m length or width. Live-bearing (ovoviviparous).