Threespot Damselfish are yellowish brown with dark verticle lines when mature and mostly just yellow when young. When young they have a black spot on top just before the tail and they have a large black spot below the middle rear of the dorsal fin.
They inhabit coral reefs. They feeds mainly on algae but also on harpacticoid copepods, small gastropods, eggs of mollusks, sponges, polychaetes and hydroids. Juveniles subsist on the external parasites of fishes.