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Class - Osteichthyes
Class Osteichthyes includes all bony fishes. Like all fishes, Osteichthyes are cold-blooded vertebrates that breathe through gills and use fins for swimming. Bony fishes share several distinguishing features: a skeleton of bone, scales, paired fins, one pair of gill openings, jaws, and paired nostrils.
Osteichthyes includes the largest number of living species of all scientific classes of vertebrates, more than 28,000 species.
Osteichthyes account for about 96% of all fish species. Fishes not included in the Osteichthyes are the Chondrichthyes (sharks and their relatives), the Myxini (hagfishes), and the Cephalaspidomorphi (lampreys).
Living Osteichthyes are divided into three subclasses: Dipnoi, Crossopterygii, and Actinopterygii.
The subclass Dipnoi (lungfishes) is characterized by an upper jaw fused to the braincase, fused teeth, and the presence of an air-breathing organ that opens to the esophagus. A lungfish's caudal fin is continuous with its dorsal and anal fins. Its pelvic and pectoral fins are long and tubular.
The subclass Crossopterygii (coelacanths) is characterized by a type of primitive scale called a
, two dorsal fins, and fleshy paired fins that contain skeletal elements. Scientists used to think that this entire subclass of fishes was extinct. Then in 1938, a living coelacanth (
) was discovered off the coast of Southeast Africa. Several specimens have since been collected.
The subclass Actinopterygii includes all other living bony fishes. Actinopterygians are characterized by fins that are supported by bony elements called rays.
Orders and Families
All orders of bony fishes end in the suffix "iformes".
While there is debate over how certain fishes should be classified, scientists recognize more than 500 different bony fish families. The names of bony fish families all end in the suffix "dae".
Genera and Species
More than 28,000 species of bony fishes have been documented. It's likely that many more, including some deep-sea species, have yet to be identified.
Primitive fishes date back to the Cambrian period, about 550 million years ago. These jawless fishes lived relatively unchanged over the following 100 million years.
The Devonian period, about 360 to 400 million years ago, is known as the "Age of Fishes", because of the abundance and diversity of fishes that appeared during this period.
In the Devonian, fishes began to develop jaws and paired fins. All four living classes of fishes and the three subclasses of Osteichthyes were established by the mid-Devonian.
Many species of fish that lived during the Devonian are now extinct.
Bony fishes continued to evolve after the Devonian period.
Most modern orders of bony fishes probably evolved during the Triassic period, about 200 million years ago.
Today, the Actinoptergians are the dominant vertebrates in the oceans and in freshwater systems.
The most recently evolved orders of bony fishes include the Pleuronectiformes (flatfishes) and Tetraodontiformes (triggerfishes, pufferfishes, and molas).