Rayfinned

Ray-finned fishes, or actinopterygians, are fishes whose fins are webs of skin stiffened by bony or horny rays. They form the largest and most diverse group of fishes, comprising the majority of living vertebrates. They are distinguished from the lobe-finned fishes (sarcopterygians), which have fleshy, lobed fins with a robust internal skeleton.

Anatomy and variation: The vast majority have a bony skeleton and fins supported by lepidotrichia, or fin rays. They typically have cycloid or ctenoid scales, a swim bladder for buoyancy, and an operculum covering the gills. The caudal fin and dorsal and anal fin shapes vary widely, reflecting different ecological roles.

Classification and evolution: Actinopterygii includes the Teleostei, which encompasses most living ray-finned fishes. The earliest ray-finned fishes appeared in the Paleozoic, with major radiations in the Mesozoic and Cenozoic. They are contrasted with Sarcopterygii, the lobe-finned fishes that gave rise to tetrapods.

Distribution and ecology: Ray-finned fishes occupy nearly all aquatic habitats, from freshwater rivers to open oceans, reefs, and deep seas. They range from tiny gobies to large tunas and mola sunfishes, and include many species essential to ecosystems and human economies.

Economic and scientific significance: They include numerous food fishes (salmon, cod, tuna) and ornamental species. The zebrafish is a widely used model organism in developmental biology and genetics.