The Moorish idol (Zanclus cornutus) is a species of marine ray-finned fish belonging to the family Zanclidae.

The Moorish idol was first formally described as Chaetodon cornutus in 1758 by Carl Linnaeus in the 10th edition of the Systema Naturae with "Indian Seas" given as its type locality.

The species, Angiolinia mirabilis, was described by Giorgio Carnevale and James C. Tyler in 2024 based on three specimens found in Bolca, Italy.

Carnevale & Tyler found that Zanclus cornutus and Angiolinia mirabilis form a derived clade distinguishable from Eozanclus brevirostris by one supernumerary spine on the first dorsal-fin pterygiophore, one uroneural in the caudal skeleton, and distally filamentous dorsal-fin spines (except the first two fins).

[10][11] The genus name Zanclus is derived from the Ancient Greek word zanklon, meaning "sickle", and is an allusion to the long curved dorsal fin.

[12] The Moorish idol's body is highly compressed and disc-like in shape with a tube-like snout and small bony protuberances above the eyes in adults.

[10] The dorsal fin is supported by 6 or 7 spines, which are elongated into a long filament which resembles a whip, and between 39 and 45 soft rays.

[10] Like their closely related family, the Acanthuridae, the Moorish idol has larvae that are specialized for a long pelagic life stage.

[14] In the postflexion stage, the Moorish idol larvae have fully developed fins, their body form is compressed and deep-bodied.

[17][18] Although, Moorish idols are omnivores, they mostly feed on sponges, as well as, algae, coral polyps, tunicates and other benthic invertebrates.

[16][19][20] A gut content analysis study shows that sponges make up about 70% of the total weight consumed by Moorish idols.

These substitutes are all butterflyfishes of the genus Heniochus and include the pennant coralfish, H. acuminatus; threeband pennantfish, H. chrysostomus and the false Moorish idol, H.