Bony Fishes
The skeleton contains, at least in part, true bone. The skull has sutures. Teeth are usually attached to bone. Fin rays are dermal in origin, bilateral, and may be either unbranched, ossified and rigid, forming spines (often rather threatening), or though being ossified, still are soft and flexible, or they are branched and segmented, consisting of numerous small elements. The upper jaw is usually formed by the maxillaries and premaxillaries, these bones are dermal in origin. A swim bladder is usually present; this structure is used as a functional lung in some and as a hydrostatic organ in others. An intestinal spiral valve is found in only a few of the more generalized groups. Internal fertilization is relatively rare. The caudal fin is primitively heterocercal but becomes homocercal in more advanced groups.
Common character of the Teleostei are the round or elasmoid scales, consisting of bony tissue only, without any covering of enamel or ganoine or related compounds. The classification of the scales in cycloid and ctenoid scales, dependent on whether their outer edge is smooth or spiny, however, is of little meaning because several fish may have both kinds at the same time. It may be a good feature within a family or genus, but not suited to separate higher taxa.
After Fritzsche and Fuiman, 1982.