Euteleosts

Euteleostei, or euteleosts, is a large clade of ray-finned fishes within the teleosts (Actinopterygii). They constitute the majority of living teleost species, representing the most species-rich and ecologically diverse portion of the group. The clade includes many familiar fishes across a wide range of habitats, from oceans to freshwater systems.

Taxonomy and evolution: Euteleostei is one of the principal subdivisions of Teleostei. In many modern classifications it is divided into major lineages such as Protacanthopterygii and Neoteleostei, the latter containing most living orders. The exact relationships among euteleost lineages have been refined repeatedly through anatomical studies and molecular analyses, reflecting the group's long and complex evolutionary history.

Characteristics: Euteleosts are distinguished by a set of derived features that separate them from more primitive teleosts. While specific traits vary among lineages, the group is characterized by substantial diversification in the feeding apparatus and sensory systems, along with broad morphological variety. The clade encompasses a remarkable range of body forms, ecological roles, and life-history strategies.

Diversity and ecology: Euteleosts inhabit virtually every aquatic environment, from deep oceans to freshwater lakes and rivers. They include taxa such as salmonids, cods, herrings, perches, flatfishes, and many others. This diversity supports a wide array of ecological interactions, from predation and herbivory to parasitism and symbiosis, and underpins significant economic value in fisheries and aquaculture.

Fossil record and significance: The euteleost crown group appears in the fossil record during the Late Jurassic to Early Cretaceous, with extensive diversification in the Cretaceous and later. Today, euteleosts dominate many fish faunas and are central to global biodiversity and human economies.