Acanthuroidei

Physical characteristics

Species assigned to Acanthuroidei typically have small, closely set scales and bodies that are deeper than long, giving a tall, narrow profile. Many have continuous or closely linked dorsal and anal fins and a variety of tail shapes, from truncate to lunate. A distinctive feature of the surgeonfishes (family Acanthuridae) is the movable, scalpel-like spine on each side of the caudal peduncle used in defense. Mouth and teeth morphology varies according to diet, from comb-like teeth for scraping algae to more generalized dentitions in omnivorous forms.

Principal families

• Acanthuridae — surgeonfishes, tangs and unicornfishes; important algal grazers on reefs.
• Zanclidae — the moorish idol (represented by Zanclus cornutus), a distinctive reef species.
• Luvaridae — the luvar (Luvarus imperialis), an uncommon open-water species.
• Ephippidae — spadefishes and batfishes, laterally compressed and often reef-associated.
• Drepaneidae — sicklefishes, with deep bodies and moderately elongated fins.
• Scatophagidae — scats, often estuarine or coastal and tolerant of variable salinity.
• Monodactylidae — moonyfishes, laterally compressed and sometimes kept in aquaria.

Overall the suborder contains several dozen to a few hundred described species distributed across these families; exact composition has been revised repeatedly as molecular studies refine relationships.

Most acanthuroideans inhabit shallow coastal waters, coral reefs and adjacent seagrass or rocky areas in tropical and subtropical oceans. Some families include species that use estuaries and brackish habitats. Diets span strict herbivory (important for controlling algal growth), omnivory and planktivory, so members contribute to multiple trophic pathways on reefs and in coastal food webs.

Taxonomically, Acanthuroidei has a complex history. The name derives from Greek akantha (“thorn” or “spine”) and oura (“tail”), a reference to the caudal spines of surgeonfishes. Recent phylogenetic work has sometimes treated the group at different ranks or redistributed families between orders, reflecting ongoing revision of percomorph relationships. For a traditional overview within Perciformes see Perciformes.