Temporal range: Early Triassic–Recent 
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Retroculus lapidifer (Perciformes: Cichlidae)
Hairy Blenny, Labrisomus nuchipinnis
Blue Tang, Acanthurus coeruleus
Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in the Triassic period, includes 26,840 extant species in about 40 orders and 448 families; most living fishes are members of this group. The other two infraclasses, Holostei and Chondrostei, may be paraphyletic.
Teleosts have a movable maxilla and premaxilla and corresponding modifications in the jaw musculature. These modifications make it possible for teleosts to protrude their jaws outwards from the mouth. The caudal fin is homocercal, meaning the upper and lower lobes are about equal in size. The spine ends at the caudal peduncle, distinguishing this group from those in which the spine extends into the upper lobe of the caudal fin.
Systematics and evolution 
The oldest teleost fossils date back to early Triassic. Teleosts are here divided into twelve superorders, but this system is unlikely to be entirely correct and is in the process of being studied.
- Superorder Osteoglossomorpha
- Superorder Elopomorpha
- Superorder Clupeomorpha
- Superorder Ostariophysi
- Order Gonorynchiformes, including the milkfishes
- Order Cypriniformes, including barbs, carp, danios, goldfishes, loaches, minnows, rasboras
- Order Characiformes, including characins, pencilfishes, hatchetfishes, piranhas, tetras.
- Order Gymnotiformes, including electric eels and knifefishes
- Order Siluriformes, the catfishes
- Superorder Protacanthopterygii
- Superorder Stenopterygii (may belong in Protacanthopterygii)
- Superorder Cyclosquamata (may belong in Protacanthopterygii)
- Superorder Scopelomorpha
- Superorder Lampridiomorpha
- Superorder Polymyxiomorpha
- Superorder Paracanthopterygii
- Superorder Acanthopterygii
- Order Mugiliformes, the mullets
- Order Atheriniformes, including silversides and rainbowfishes
- Order Beloniformes, including the flyingfishes
- Order Cetomimiformes, the whalefishes
- Order Cyprinodontiformes, including livebearers, killifishes
- Order Stephanoberyciformes, including the ridgeheads
- Order Beryciformes, including the fangtooths and pineconefishes
- Order Zeiformes, including the dories
- Order Gobiesociformes, the clingfishes
- Order Gasterosteiformes including sticklebacks, pipefishes, seahorses
- Order Syngnathiformes, including the seahorses and pipefishes
- Order Synbranchiformes, including the swamp eels
- Order Tetraodontiformes, including the filefishes and pufferfish
- Order Pleuronectiformes, the flatfishes
- Order Scorpaeniformes, including scorpionfishes and the sculpins
- Order Perciformes 40% of all fish including anabantids, bass, cichlids, gobies, gouramis, mackerel, perches, scats, whiting, wrasses
- Palmer, Douglas (1999). The Marshall Illustrated Encyclopedia of Dinosaurs & Prehistoric animals. London: Marshall Editions Developments Ltd. ISBN 3-8290-6747-X.
- Miller, Stephen, and John P. Harley. Zoology, Seventh Edition, pg 297. McGraw-Hill Higher Education. New York, 2007.
- Benton, Michael J. (1990). Vertebrate Paleontology. London: Chapman & Hall. ISBN 0-412-54010-X.
- Ben Waggoner (1995-07-17). "Telostei". Museum of Paleontology, University of California, Berkeley. Retrieved 2006-06-08.
- In ITIS, Gobiesociformes is placed as the suborder Gobiesocoidei of the order Perciformes.
- In ITIS, Syngnathiformes is placed as the suborder Syngnathoidei of the order Gasterosteiformes.