Acanthuridae ("thorn tail") is the family of surgeonfishes, tangss, and unicornfishes. The family includes about 80 species in six genera, all of which are marine fish living in tropical seas, usually around coral reefs. Many of the species are brightly colored and extremely popular for aquaria.
The distinctive characteristic of the family is a pair of spines, one on either side of the tail, and sharp enough to cause injury to the unwary. Both the dorsal and anal fins are large, extending for most of the length of the body. The small mouths have a single row of teeth used for grazing on algae.
Most species are small, ranging up to 30 cm, but the whitemargin unicornfish Naso annulatus can reach a meter in length.