Teleosts are a group of ray-finned fishes and are one of the largest group of living vertebrates. The group includes more than 20,000 species of fishes. For all their diversity, there are a few traits that unify the teleosts. One is their tail, it consist of two lobes of equal size. Another trait of the teleosts is their jaw. It's unique among fish in that the bones of the upper jaw (which include the maxilla and the premaxilla) are highly mobile. This enables teleosts to protrude their jaw out away from their face when opening their mouth. And that's makes a teleost's mouth all the better to catch prey with.