Characteristics
Osteichthyans are characterized by a relatively stable pattern of cranial bones, rooted, medial insertion of mandibular muscle in lower jaw. The head and pectoral girdles are covered with large dermal bones. The eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species. The labyrinth in the inner ear contains large otoliths. The braincase, or neurocranium, is frequently divided into anterior and posterior sections divided by a fissure.
Bony fish typically have swim bladders, which helps the body create a neutral balance between sinking and floating. However, these are absent in many species, and have developed into primitive lungs in the lungfishes. They do not have fin spines, but instead support the fin with lepidotrichia (bone fin rays). They also have an operculum, which helps them breathe without having to swim.
They also are able to see in colour, unlike most other fish.
Bony fish have no placoid scales. Mucous glands coat the body. Most have scales of sort: ganoid, cycloid, or cytenoid. These scales are smooth and overlapping.
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