The butterflyfish are a group of conspicuous tropicalmarine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group. The approximately 129 species in 12 genera are found mostly on the reefs of the Atlantic, Indian, and Pacific Oceans. A number of species pairs occur in the Indian and Pacific Oceans, members of the huge genus Chaetodon. Butterflyfish look like smaller versions of angelfish, but unlike these, lack preopercle spines at the gill covers. Some members of the genus Heniochus resemble the Moorish idol of the monotypic Zanclidae. Among the paraphyleticPerciformes, the former are probably not too distantly related to butterflyfish, whereas the Zanclidae seem far less close.
Butterflyfish mostly range from in length. The largest species, the lined butterflyfish and the saddle butterflyfish, C. ephippium, grow to. The common name references the brightly coloured and strikingly patterned bodies of many species, bearing shades of black, white, blue, red, orange, and yellow. Other species are dull in colour. Many have eyespots on their flanks and dark bands across their eyes, not unlike the patterns seen on butterfly wings. Their deep, laterally narrow bodies are easily noticed through the profusion of reeflife. The conspicuous coloration of butterflyfish may be intended for interspecies communication. Butterflyfish have uninterrupted dorsal fins with tail fins that may be rounded or truncated, but are never forked. Generally diurnal and frequenting waters less than deep express such an armored stage.
The Chaetodontidae can be, but are not usually, divided into two lineages that arguably are subfamilies. The subfamily name Chaetodontinae is a little-used leftover from the period when the Pomacanthidae and Chaetodontidae were united under the latter name as a single family. Hence, Chaetodontinae is today considered a junior synonym of Chaetodontidae. In any case, one lineage of Chaetodontidae contains the "typical" butterflyfish around Chaetodon, while the other unites the bannerfish and coralfish genera. As the Perciformes are highly paraphyletic, the precise relationships of the Chaetodontidae as a whole are badly resolved. Before DNA sequencing, the taxonomy was confused about whether to treat these as species or subspecies. Also, numerous subgenera have been proposed for splitting out of Chaetodon, and it is becoming clear how to subdivide the genus if that is desired. The fossil record of this group is marginal. Their restriction to coral reefs means their carcasses are liable to be dispersed by scavengers, overgrown by corals, and any that do fossilize will not long survive erosion. However, Pygaeus, a very basalfossil from the mid- to late Eocene of Europe, dates from around the Bartonian 40–37 million years ago. Thus, the Chaetodontidae emerged probably in the early to mid-Eocene. A crude molecular clock in combination with the evidence given by Pygaeus allows placement of the initial split between the two main lineages to the middle to late Eocene, and together with the few other fossils, it allows the deduction that most living genera were probably distinct by the end of the Paleogene 23 Mya.
Genera
The bannerfish-clown fish are the same fish because of how they look these might be considered tribes, but have not been formally named. Genera are listed in order of the presumed phylogeny, from the most ancient to the youngest:
