Acanthuridae is the family of surgeonfishes, tangs, and unicornfishes. The family includes about 86 extant species. The family is composed of marine fish living in tropical seas, usually around coral reefs. Many of the species are brightly colored and popular for aquaria. The distinctive characteristic of the family is the scalpel-like spines, one or more on either side of the tail ("thorn tails"), which are dangerously sharp. The dorsal, anal, and caudal 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.