The Characiformes form part of a series called the Otophysi within the superorder Ostariophysi. They are the sole group in the clade Anotophysi, a subgroup of the superorder Ostariophysi. Like other orders of the Ostariophysi, fishes of Cypriniformes possess a Weberian apparatus. Ostariophysi, which includes most freshwater fishes, have developed some unique adaptations. Gymnotiformes are among the more derived members of Ostariophysi, a lineage of primary freshwater fishes. The monophyly of Ostariophysi has come into question with molecular evidence. The clade Otocephala includes the Clupeiformes (herrings) and Ostariophysi (carps, catfishes and allies). Ostariophysi is the second largest teleost superorder. Ostariophysi is the second-largest superorder of fish.