Revision of the hirsuticornis‐like species of Macrothrix Baird, 1843 (Cladocera: Anomopoda: Macrothricidae) from Subantarctic and temperate regions of the southern hemisphere

Abstract

The aim of this paper is to revise populations of Macrothrix cf. hirsuticornis (Cladocera: Anomopoda: Macrothricidae) from different regions of the southern hemisphere. It is demonstrated that M. hirsuticornis Norman and Brady, 1867 s. str. is absent there, and five related species occupy different Subantarctic islands and the southernmost portions of South America, and Africa. Macrothrix boergeni Studer, 1878 from the Kerguelen Archipelago is redescribed and a neotype is selected. All populations in the southernmost portion of continental South America, Tierra del Fuego, Falklands, South Georgia, South Orkney Islands, and on the Antarctic Peninsula belong to M. oviformis Ekman, 1900. All the taxa described from this region—M. ciliata Vávra, 1900, M. odontocephala Daday, 1902, M. propinqua Sars, 1909, and, probably, M. inflata Daday, 1902—are junior synonyms of M. oviformis. Two new species are established: M. sarsi sp. nov. from the Cape region of South Africa and M. ruehei sp. nov. from Crozet, Marion islands, and Île Amsterdam. Macrothrix cf. flagellata Smirnov and Timms, 1983, previously known only from Tasmania, is found on Macquarie Island too. Differences between species from the southern hemisphere and Palaearctic M. hirsuticornis are summarized. It is demonstrated that characters of the general body shape (i.e. presence of a hood or a tooth on posterior head border) have a limited value for the systematics of Macrothrix. In contrast, some fine details, mostly missed by previous authors, are valuable for species discrimination. The present study increases the number of species recorded from the Antarctic‐Subantarctic region. Probably, the current pattern of Macrothrix distribution results from a disruption of a pan‐continental (early Mesozoic?) species complex.