Ostariophysi

Superorder of fishes

Ostariophysi is the second largest superorder of fish. Members of this superorder are called ostariophysians. This diverse group contains 10,758 species, about 28% of known fish species in the world and 68% of freshwater species, and are present on all continents except Antarctica. They have a number of common characteristics such as an alarm substance and a Weberian apparatus. The superorder is classified below:
Series Anotophysi
Gonorynchiformes, about 37 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). 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 Cyprinoformes 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. 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.

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 is made up of a set of bones known as Weberian ossicles, a chain of small bones that connect the auditory system to the gas bladder of fishes. The ossicles connect the gas bladder wall with Y shaped lymph sinus that abuts the lymph filled transverse canal joining the sacculi of the right and left ears. This allows the transmission of vibrations to the inner ear. In anotophysians, the three first vertebrae are specialized and associated with one or more cephalic ribs (a primitive Weberian apparatus). In the otophysians, a distinct modification of the anterior four or five first vertebrae is found, as well as the Weberian ossicles. The fully functioning Weberian apparatus consists of the swim bladder, the Weberian ossicles, a portion of the anterior vertebral column, and some muscles and ligaments. It is named after the German anatomist and physiologist Ernst Heinrich Weber who first described the Weberian ossicles.