Ostariophysi

Most species possess a swim bladder (except in Gonorynchus). The swim bladder is usually divided into two chambers. A smaller anterior chamber is partially or completely covered by a silvery peritoneal tunic. A larger posterior chamber may be reduced or absent in some groups. Minute, unicellular, horny projections known as "unculi" are commonly present on various body parts and are only known from ostariophysians. It also contains a number of species considered to be some of the smallest vertebrates extant; Danionella translucida at in length, and Paedocypris progenetica at . The families Malapteruridae and Gymnotidae have the ability to produce strong electric charges; they are considered among the prototypical electric fishes. == Taxonomy ==

The superorder is divided into two series, Anotophysi and Otophysi. However, in older literature, Ostariophysi was restricted only to the fish that are currently classified under Otophysi. The superorder is classified below: • Series Anotophysi • Gonorynchiformes, about 107 species • Series Otophysi (Euostariophysi) • Cypriniformes (minnows and allies), about 4,501 species (contains Cyprinidae, largest family of freshwater fishes) • Characiformes (characins and allies), about 2,168 species • Siluriformes (catfishes), about 3,813 species • Gymnotiformes (electric eels, American knifefishes), about 239 species (sometimes grouped under Siluriformes) The monophyly of Ostariophysi has come into question with molecular evidence. Gonorynchiformes is more closely related to Clupeiformes than Otophysi. It is possible that the Gonorynchiformes and Clupeiformes form a monophyletic group. There is evidence for a sister group relationship between Ostariophysi and Clupeomorpha (the taxon Ostarioclupeomorpha, also known as Otocephala, was coined to describe this possibly monophyletic group). resources such as the National Center for Biotechnology Information (NCBI) continue using this treatment, though some researchers prefer to treat it as monotypic, containing just Characiformes. The following primitive fossil ostariophysans are known:'''''' • Series Otophysi • Genus Acronichthys Liu et al., 2025 (Late Cretaceous of the western United States and Canada)''' ==Evolution==

Ostariophysian fossils, both anotophysan and otophysian, are known from the early Cretaceous. Ostariophysian fossils are known from every continent except Australia. The Otophysi originated in freshwaters during the Jurassic (c. 200–145 Ma) before the breakup of the super continent Pangea. The division of the Otophysi into the four extant clades closely follows the breakup of Pangea. The separation of Laurasia in the north from Gondwana in the south isolated the lineages which gave rise to the modern Cypriniformes and Characiphysi. The Characiphysi then was itself divided into the diurnal (day-active) Characiformes and the nocturnal (night-active) Siluriphysi, including Siluriformes and Gymnotiformes. Modern Characiformes are present in both South America and Africa, and have relatively recently extended their range to North America. The Siluriphysi are characterized by many derived traits, including notably, electroreception. The Siluriphysi originated before the breakup of Gondwana into South America and Africa in the Aptian (c. 110 Ma) but the presence of several basal Siluriphysan taxa in modern South America (Gymnotiformes, Diplomystidae, Loricaridea) suggest that the Siluriphysi may have originated on the western portion of Gondwana. Alternatively, these basal taxa have subsequently become extinct in Africa. The modern distribution of Siluriformes is cosmopolitan due to subsequent dispersal. ==References==