The Teleosts are by far the largest infraclass, the Teleostei, in the class Actinopterygii, the ray-finned fishes. The other two infraclasses are the Holostei (bowfins and garfish) and the paraphyletic Chondrostei (sturgeons and reedfish). The name is derived from Greek (teleios, "complete" + osteon, "bone"). This diverse group, which arose in the Triassic period, has over 26,000 members, arranged in about 40 orders and 448 families. Teleosts range from giant oarfish, measuring or more, and ocean sunfish weighing over two tons, to the minute male anglerfish Photocorynus spiniceps, just long. As well as torpedo-shaped fish built for speed, teleosts can be flattened vertically or horizontally, be elongated cylinders or take bizarre shapes like anglerfish and seahorses that are hardly recognisable as fish. Ninety-six percent of all fish are teleosts; they dominate the seas from pole to pole and inhabit the ocean depths, estuaries, rivers, lakes and even swamps.

The Teleosts are by far the largest infraclass, the Teleostei, in the class Actinopterygii, the ray-finned fishes. The other two infraclasses are the Holostei (bowfins and garfish) and the paraphyletic Chondrostei (sturgeons and reedfish). The name is derived from Greek (teleios, "complete" + osteon, "bone"). This diverse group, which arose in the Triassic period, has over 26,000 members, arranged in about 40 orders and 448 families. Teleosts range from giant oarfish, measuring or more, and ocean sunfish weighing over two tons, to the minute male anglerfish Photocorynus spiniceps, just long. As well as torpedo-shaped fish built for speed, teleosts can be flattened vertically or horizontally, be elongated cylinders or take bizarre shapes like anglerfish and seahorses that are hardly recognisable as fish. Ninety-six percent of all fish are teleosts; they dominate the seas from pole to pole and inhabit the ocean depths, estuaries, rivers, lakes and even swamps.