What's a teleost? Let's see what Wikipedia has to offer...
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.
Alright: Teleosts are ray-finned fish that developed 200 to 250 million years ago, making them evolutionarily "advanced" relative to some ancient fish species. About 80 percent of the world's 25,000 fish species are teleosts.
When Wells Reserve scientists study fish, they invariably focus on teleosts. So as we develop a simple guide to our region's coastal fish species — due this spring — only one non-teleost ekes its way in.