Teleostei

Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in the Triassic period, includes 20,000 extant species in about 40 orders. The other two infraclasses, Holostei and Chondrostei, are paraphyletic.

On the basis of biomass as well as of species count, teleosts are the typical vertebrates, and all other vertebrates are exceptions to the teleost rule. See Actinopterygii for a complete list of orders.

Characteristics
Teleosts have a movable maxilla and premaxilla and corresponding modifications in the jaw musculature. These modifications make it possible for teleosts to protrude their jaws outwards from the mouth. The caudal fin is homocercal, meaning the upper and lower lobes are about equal in size. The spine ends at the caudal peduncle, distinguishing this group from those in which the spine extends into the upper lobe of the caudal fin.