Acanthurus is a genus of marine ray-finned fish belonging to the family Acanthuridae, which includes the surgeonfishes, unicornfishes and tangs, found in the Atlantic, Indian and Pacific Ocean. They are found in tropical oceans, especially near coral reefs, with most species in the Indo-Pacific but a few are found in the Atlantic Ocean. As other members of the family, they have a pair of spines, one on either side of the base of the tail which are dangerously sharp.

Taxonomy

Acanthurus was first proposed as a subgenus of Chaetodon in 1775 by the Swedish-speaking Finnish explorer, orientalist and naturalist Peter Forsskål, although he recognised that it was probably different from Chaetodon even at the family level. In 1856 Desmarest designated Teuthis hepatus, which had been described from a type now known to have been collected at Ambon Island in the Moluccas (other erroneous type localities were named) in 1758 by Linnaeus, as the type species of the genus. T. hepatus is a synonym of Paracanthurus hepatus and this would make Paracanthurus synonymous with Acanthurus. An alternative would be to use the name Harpurus proposed as a monospecific genus in 1788 by Johann Reinhold Forster when he described Harpurus fasciatus, a synonym of Acanthurus triostegus. It has been proposed that the International Commission on Zoological Nomenclature should be petitioned to stabilise the genera Acanthurus and Paracanthurus. In 2014 it was proposed that the type species of Acanthurus should be Chaetodon sohal, which had also been described by Forsskål in 1775 as a member of the subgenus alongside C. bifasciatus, C. nigrofuscus and C. unicornis, and had been designated as the type species by Jordan and Evermann in 1917.

It has been proposed that the genus Ctenochaetus should be merged with Acanthurus, as Acanthurus is currently paraphyletic. All Ctenochaetus species are nested within Acanthurus, while A. nubilis and A. pyroferus are furthermore nested within Ctenochaetus. The 5th edition of Fishes of the World recognises these two genera as valid and classifies them as the two genera in the tribe Acanthurini of the subfamily Acanthurinae within the family Acanthuridae.

Etymology

The genus name Acanthurus comes from Ancient Greek ἄκανθα (ákantha), meaning "spine", and οὐρά (ourá), meaning "tail", a reference to the scalpel-like bony plates on the caudal peduncle, these also give rise to the vernacular English names surgeonfish and doctorfish.

Evolution

Fossil remains of Acanthurus are known from the Middle Miocene of the former Paratethys region, including Austria, Croatia, Hungary, and Ukraine. The specimens from Austria and Ukraine are assigned to the extinct species †Acanthurus haueri. Their presence coincides with the Middle Miocene Climatic Optimum, and they likely inhabited coralgal and bryozoan-dominated reefs. Previously, specimens from Monte Bolca in Italy were also assigned to the modern Acanthurus, but they have since been split into their own genera.

Distribution

Acanthrus surgeonfishes are distributed around the world in tropical waters.

Species

There are currently 41 recognized species in this genus:

Fossil species

• †Acanthurus haueri (von Meyer, 1842) (Middle Miocene of Austria and Ukraine)

Characteristics

Acanthurus surgeonfishes have disc shaped, highly laterally compressed bodies with a steep dorsal profile to the head. They have a small mouth positioned low on the head and the fish can protrude the jaws. The 8 to 28 teeth in the jaws are fixed and have flattened, serrated tips. There are typically 11 spines in the dorsal fin. There is a single spine on each side of the caudal peduncle and these can be pressed down into a groove.

The Indo-Pacific yellowfin surgeonfish (A. xanthopterus) is the largest species with a maximum published total length of while the smallest is the black-barred surgeonfish (A. polyzona) with a maximum published total length of .

References