The Moorish idol, Zanclus cornutus (“crowned scythe”), is a small marine fish species, the sole extant representative of the family Zanclidae in order Perciformes. A common inhabitant of tropical to subtropical reefs and lagoons, the Moorish idol is notable for its wide distribution throughout the Indo-Pacific. The Moorish idol got its name from the Moors of Africa, who purportedly believed the fish to be a bringer of happiness. Moorish idols are also popular aquarium fish, but despite their popularity, they are notorious for short aquarium lifespans and sensitivity. With distinctively compressed and disk-like bodies, Moorish idols stand out in contrasting bands of black, white, and yellow, which makes them attractive to aquarium keepers. The fish have relatively small fins, except for the dorsal fin, whose six or seven spines are dramatically elongated to form a trailing, sickle-shaped crest called the philomantis extension. Moorish idols have small terminal mouths at the end of long, tubular snouts; many long bristle-like teeth line the mouth. The eyes are set high on the fish's deeply keeled body; in adults, perceptible bumps are located above each. The anal fin may have two or three spines. Moorish idols reach a maximum length of 23 cm (9.1 in). The sickle-like dorsal spines shorten with age. Generally denizens of shallow waters, Moorish idols prefer flat reefs. The fish may be found at depths from 3 to 180 m (9.8 to 590 ft), in both murky and clear conditions. Their range includes East Africa, the Indian Ocean and the Ducie Islands; Hawaii, southern Japan, and all of Micronesia; they are also found from the southern Gulf of California south to Peru.