structural:summarization, linguistic:paraphrasing, structural:reformatting, information:filtering
Taxonomy

The Characiformes form part of a series called the Otophysi within the superorder Ostariophysi. The Otophysi contain three other orders, Cypriniformes, Siluriformes, and Gymnotiformes. The Characiformes form a group known as the Characiphysi with the Siluriformes and Gymnotiformes. The order 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, 18 families, about 270 genera, and at least 1674 species are known.

The suborder Citharinoidei, which contains the families Distichodontidae and Citharinidae, is considered the sister group to the rest of the characins, suborder Characoidei. This group has a very ancient divergence from the rest of the Characiformes, dating back to the Early Cretaceous or earlier, and it has been suggested that it be better treated as its own order, the Cithariniformes.