The commonest caligid copepod infesting commercial salmonid netpen systems in southern Chile is described as a new species, Caligus rogercresseyi. This species belongs to the macarovi-group of species within the genus. It differs from Caligus flexispina Lewis 1964, with which it has previously been confused, in several important characters. These include the relatively elongate caudal rami, the proportions of the female genital complex and of the male abdomen, and the armature and ornamentation of the antenna in both sexes. The form of the sensillae associated with the postantennal process and the form of the male maxilliped are identified as possible additional diagnostic characters of the macarovi-group.