actinopterygian

Actinopterygii, or ray-finned fishes, are a clade of bony fishes characterized by fins supported by numerous slender bony rays called lepidotrichia. They constitute the largest and most diverse group of fishes, including the majority of living vertebrate species. The group comprises several major lineages, notably Holostei (gars and bowfins) and Teleostei, which contains most living species, with chondrosteans such as sturgeons and paddlefishes representing a more primitive subset.

Anatomical features common to actinopterygians include a predominantly bony skeleton, webs of skin between the fin rays, an open gill cover (operculum), and a gas-filled swim bladder used for buoyancy. Many have a mobile upper jaw allowing protrusion. Scales are diverse, ranging from ganoid in some primitive forms to cycloid or ctenoid in most teleosts. The lateral line system, well developed in most species, detects water movements. The tail is often homocercal in modern teleosts.

Ecology and distribution: Ray-finned fishes occupy virtually all aquatic environments, from freshwater rivers and lakes to the open ocean, including coral reefs and deep-sea habitats. They exhibit extensive ecological and morphological diversity, with feeding strategies from herbivory to predation and a wide range of life histories.

Evolution and fossil history: Actinopterygii first appear in the fossil record during the Paleozoic, with a rich record beginning in the Silurian and Devonian. They underwent multiple radiations and now dominate almost all modern fish diversity, with teleosts alone accounting for the vast majority of species.