Acanthurus

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 otherwise Acanthurus is paraphyletic. 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.

Species
There are currently 41 recognized species in this genus:
 * Acanthurus achilles G. Shaw, 1803 (Achilles surgeonfish)
 * Acanthurus albimento K. E. Carpenter, J. T. Williams & M. D. Santos, 2017 (White-chin surgeonfish)
 * Acanthurus albipectoralis G. R. Allen & Ayling, 1987 (White-fin surgeonfish)
 * Acanthurus auranticavus J. E. Randall, 1956 (Orange-socket surgeonfish)
 * Acanthurus bahianus Castelnau, 1855 (Barber surgeonfish)
 * Acanthurus bariene Lesson, 1831 (Black-spot surgeonfish)
 * Acanthurus blochii Valenciennes, 1835 (Ring-tail surgeonfish)
 * Acanthurus chirurgus (Bloch, 1787) (Doctorfish tang)
 * Acanthurus chronixis J. E. Randall, 1960 (Chronixis surgeonfish)
 * Acanthurus coeruleus Bloch & J. G. Schneider, 1801 (Atlantic blue tang)
 * Acanthurus dussumieri Valenciennes, 1835 (Eye-stripe surgeonfish)
 * Acanthurus fowleri de Beaufort, 1951 (Fowler's surgeonfish)
 * Acanthurus gahhm (Forsskål, 1775) (Black surgeonfish)
 * Acanthurus grammoptilus J. Richardson, 1843 (Fine-lined surgeonfish)
 * Acanthurus guttatus J. R. Forster, 1801 (White-spotted surgeonfish)
 * Acanthurus japonicus (P. J. Schmidt, 1931) (Japan surgeonfish)
 * Acanthurus leucocheilus Herre, 1927 (Pale-lipped surgeonfish)
 * Acanthurus leucopareius (O. P. Jenkins, 1903) (White-bar surgeonfish)
 * Acanthurus leucosternon E. T. Bennett, 1833 (Powder-blue surgeonfish)
 * Acanthurus lineatus (Linnaeus, 1758) (Lined surgeonfish)
 * Acanthurus maculiceps (C. G. E. Ahl, 1923) (White-freckled surgeonfish)
 * Acanthurus mata (G. Cuvier, 1829) (Elongate surgeonfish)
 * Acanthurus monroviae Steindachner, 1876 (Monrovia surgeonfish)
 * Acanthurus nigricans (Linnaeus, 1758) (White-cheek surgeonfish)
 * Acanthurus nigricauda Duncker & Mohr (de), 1929 (Epaulette surgeonfish)
 * Acanthurus nigrofuscus (Forsskål, 1775) (Brown surgeonfish)
 * Acanthurus nigroris Valenciennes, 1835 (Blue-lined surgeonfish)
 * Acanthurus nigros Günther, 1861 (Grey-head surgeonfish)
 * Acanthurus nubilus (Fowler & B. A. Bean, 1929) (Pin-striped surgeonfish)
 * Acanthurus olivaceus Bloch & J. G. Schneider, 1801 (Orange-spot surgeonfish)
 * Acanthurus polyzona (Bleeker, 1868) (Black-barred surgeonfish)
 * Acanthurus pyroferus Kittlitz, 1834 (Chocolate surgeonfish)
 * Acanthurus randalli J. C. Briggs & D. K. Caldwell, 1957
 * Acanthurus reversus J. E. Randall & Earle, 1999
 * Acanthurus sohal (Forsskål, 1775) (Sohal surgeonfish)
 * Acanthurus tennentii Günther, 1861 (Double-band surgeonfish)
 * Acanthurus thompsoni (Fowler, 1923) (Thompson's surgeonfish)
 * Acanthurus tractus F. Poey, 1860 (Ocean surgeonfish)
 * Acanthurus triostegus (Linnaeus, 1758) (Convict surgeonfish)
 * Acanthurus tristis J. E. Randall, 1993 (Indian Ocean mimic surgeonfish)
 * Acanthurus xanthopterus Valenciennes, 1835 (Yellow-fin surgeonfish)

Etymology
Acanthurus is a combination of acanthus meaning "spine" and urus 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.

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 70 cm while the smallest is the black-barred surgeonfish (A. polyzona) with a maximum published total length of 11 cm.

Distribution
Acanthrus surgeonfishes are distributed around the world in tropical waters.