teleostean

Teleostean, or Teleostei, refers to a clade of ray-finned fishes that constitutes the vast majority of living fishes. Teleostei is one of the principal lineages within Actinopterygii (the ray-finned fishes) and includes thousands of species inhabiting almost every aquatic environment. The group spans a wide range of forms, from tiny freshwater minnows to large pelagic predators and benthic flatfishes, and it contains most species that support commercial fisheries and the aquarium trade.

Key features commonly associated with teleosts include a mobile upper jaw (protrusible jaws) that allows rapid suction feeding, a typically flexible skull, and a caudal tail that is often homologous or symmetrical. The skeleton and paired fins tend to be highly derived relative to more primitive ray-finned fishes. Most teleosts have cycloid or ctenoid scales and a gas-filled swim bladder for buoyancy regulation, with some lineages showing further specialization.

Distribution and diversity: Teleosts are found in nearly all aquatic habitats, from high-altitude streams to the abyssal plain and tropical reefs. With tens of thousands of described species, they represent the dominant component of freshwater and marine fish assemblages.

Evolution and importance: The teleosts underwent a major evolutionary radiation starting in the early Cretaceous, leading to extensive ecological and morphological diversification. They are of major ecological and economic importance, including species such as tuna, salmon, cod, and cichlids, and are a major focus of evolutionary, developmental, and ecological research.