Characiformes

Characiformes is an order of ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, there are a few thousand different species (based on Wikipedia, about 2,086), including the well-known piranha and tetras.

Taxonomy

Characiformes form part of a series called Otophysi within the superorder Ostariophysi. Otophysi contains three other orders, Cypriniformes, Siluriformes, and Gymnotiformes. Characiformes forms a group known as Characiphysi with Siluriformes and Gymnotiformes. Characiformes is the sister group to the orders Siluriformes and Gymnotiformes, though this has been debated in light of recent molecular evidence.

Originally the characins were all grouped within a single family, the Characidae. Since then 18 different families have been separated out. However, classification varies somewhat, and the most recent (2011) study confirms the circumscribed Characidae as monophyletic. Currently, there are eighteen families, about 270 genera, and at least 1674 species. The suborder Citharinoidei, which contains the families Distichodontidae and Citharinidae, is considered the sister group to the rest of the characins, suborder Characoidei.