全骨类鱼上颌皮内骨不与颊部骨骼连接，短时间内可以用鱼鳔直接呼吸空气，现仅存两目：

Holostei are bony fish that retain basal characteristics inherited from an early time in their evolution. There are eight species divided among two orders, the Amiiformes represented by a single living species, the Bowfin (Amia calva), and the Lepisosteiformes, represented by seven living species in two genera, the gars. Further species are to be found in the fossil record and the group is often regarded as paraphyletic. Holosteians are closer to teleosts than are the chondrosteans, the other group intermediate between teleosts and cartilaginous fish. The spiracles are reduced to vestigial remnants and the bones are lightly ossified. The thick ganoid scales of the gars are more primitive than those of the bowfin.