The moorish idol, Zanclus cornutus ("Crowned Scythe"), is a small perciform marine fish, the sole representative of the family Zanclidae (from the Greek zagkios, "oblique"). A common inhabitant of tropical to subtropical reefs and lagoons, the moorish idol is notable for its wide distribution throughout the Indo-Pacific. A number of butterflyfishes (all of the genus Heniochus) closely resemble the moorish idol.
It is said the moorish idol got its name from the Moors of Africa, who purportedly believe the fish to be a bringer of happiness. Moorish idols are also popular aquarium fish, but despite their popularity, they are notorious for their short aquarium lifespans and difficulty.
With distinctively compressed and disk-like bodies, moorish idols stand out in contrasting bands of black, white and yellow which make them look very attractive to aquarium keepers. The fish have relatively small fins, except for the dorsal fin whose 6 or 7 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 bodies; in adults, perceptible bumps are located above each. The anal fin may have 2 or 3 spines. Moorish idols reach a maximum length of 23 cm. The sickle-like dorsal spines actually shorten with age.