Bony Fishes (Teleostei) form the most important sub-class of fishes, and include the vast majority of known forms, probably 8500 out of 10,000 species. They are the modern successors of the ancient fishes (Palæichthys), of which the direct survivors are now in the marked minority. The Teleostei appeared in all probability in the Chalk period, and have increasingly predominated over their gristly (Elasmobranchs or Chondropterygii) and heavily-armoured (Ganoidei) fore-runners. Many naturalists have found in Ganoids the direct ancestors of the Teleostei; but this is not allowed by our greatest modern authority—Dr Günther. They are, however, their geological successors.
In the bony fishes (Teleostei) the skeleton is bony, with completely formed vertebrae; the skin is usually clad in the characteristic light scales; the heart has a non-contractile swelling of the artery in front of the heart (the bulbus arteriosus); the gills are free and protected by a bony cover (operculum); the intestine has no spiral fold running down it; the nerves to the eyes simply cross one another, and do not fuse as they cross. Generally speaking, they are more active than their fore-runners.
Günther divides the bony fishes into six orders, and since these must be repeatedly mentioned, the following key, based on the same authority, and copied from Leunis' Synopsis des Thierreichs, is essential:
- I. Acanthopterygii—e.g. perch, mullet, beryx, mackerel, bull-head, lump-sucker, goby, blenny, gray-mullet, stickleback.
- II. Acanthopterygii Pharyngognathi—e.g. wrass.
- III. Anacanthini—e.g. cod, ling, sand-cel, turbot, flounder.
- IV. Physostomi—e.g. carp, minnow, flying-fish, pike, salmon, trout, herring, eel.
- V. Lophobranchii—e.g. pipe-fishes and seahorses.
- VI. Plectognathi—e.g. file-fish, coffer-fish, globe-fish, sun-fish.
The diagram classifies bony fishes based on gill structure:
- Gills comb-like:
- Pre-maxilla and upper jaw movable:
- Spinous rays on dorsal, anal, and ventral fins:
- Lower pharynx bones separate.... I.
- United..... II.
- Without spinous rays:
- Ventral fin (if present) on throat or breast; air-bladder without duct... III.
- Ventral fins posterior; air-bladder with duct..... IV.
- Spinous rays on dorsal, anal, and ventral fins:
- Pre-maxilla and upper jaw rigidly fixed to one another and to skull..... V.
- Pre-maxilla and upper jaw movable:
- Gills composed of small rounded lobes..... VI.
For further information, see the article on FISHES, and separate articles; consult Günther's Introduction to the Study of Fishes, and Huxley's Anatomy of Vertebrates.