Group of bony fish belonging to the class Actinopterygii. Often ranked as a superorder, the chondrosteans have a partly cartilaginous skeleton (see cartilage), a heterocercal tail, a spiracle, and an intestinal spiral valve. The group includes the extant orders Acipenseriformes and Polypteriformes, and the extinct order Palaeonisciformes (palaeoniscids, or ‘ancient fish’).