Chondrostei is a superorder of Actinopterygii in the class Osteichthyes. Fish with a spindle-shaped body, bare or covered with five rows of bony bugs. The mouth is lower, there is a rostrum. The upper blade of the heterocercal caudal fin has ganoid scales and fulcra. Skull with superimposed bones of skin origin. The chordae are preserved for life. There are no vertebrae. Intestine with spiral valve, heart with arterial cone. Includes an order of living fishes - Acipenseriformes with two families - Acipenseridae and Polyodontidae.
Modern cartilaginous fish reach lengths of up to 9 metres (beluga). The body is spindle-shaped. It may be covered with bony ganoid scales, five rows of bony bugs, or bare. Sometimes the scales are fused into plates. There is a rostrum, the mouth is inferior. The tail is heterocercal or shortened heterocercal, with ganoid scales and fulcra on the upper blade. The paired fins are horizontal to the body, with the anal opening close to the pelvic fins. The pelvic fins are in an abdominal position, the pectoral fins are low. The skeleton is mainly cartilaginous. The endocranium is cartilaginous with well developed cover bones. The chorda is unbranched, there are only cartilaginous arches, vertebral bodies are absent. The heart has an arterial cone, the intestine has a spiral valve. The swim bladder is connected to the oesophagus by a canal (open bladder).