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a superorder of fishes of the group Actinopterygii. The superorder occupies an intermediate place between cartilaginous fish (Chondrichthyes) and bony fish (Teleostei). The skull, jaw apparatus, and gills are similar to those of the bony fish; however, the lower jaw, which is made of numerous ossifications, and the structure of the skeleton of the caudal fin resemble those of cartilaginous ganoids.
The Holostei, which evidently evolved from the higher cartilaginous ganoids, first appeared in the late Permian period. During the Mesozoic era the Holostei were represented by seven orders, which were almost all extinct by the beginning of the Paleogene epoch. The modern Holostei include the order Cycloganoidei (with one species—the bowfin) and the order Lepisosteiformes (with several species).