Acanthogonatus nahuelbuta is a mygalomorph spider of Chile, named after its type locality: Piedra del Águila, Parque Nacional Nahuel-Buta, Malleco. Males differ from A. patagallina by having the basal portion of the bulb less rounded and the basal loop of the bulbal duct less sinuous; and from those of A. hualpen by the differently shaped embolus and the palpal tibia with the apical two-thirds (instead of its apical one-third) tapering gradually and having thickened setae.