Revision of thehirsuticornis‐like species ofMacrothrixBaird, 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, 1902are 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.

Endemism in the Cladocera (Crustacea: Branchiopoda) of Southern Africa

“…However, lower endemism in South Africa (Korovchinsky, 2006) can be attributed to an insufficient level of study, confirmed by recent findings (Kotov 2007b(Kotov , 2009Sinev, 2008Sinev, , 2009; this study). Segers and De Smet (2008) also concluded that there are few known rotifer endemics in the Cape region, but that this is probably due to the absence of data, rather than being a fact (H. Segers, personal communication).…”

“…There are doubts on their origins: they could not be regarded as primitive, but assuming that the crowngroup is very old (=possibly even as far as the Mesozoic), they could be regarded as descendants of a proto-taxon with a pan-continental distributional area. The same is true for Macrothrix sarsi, an endemic member of the hirsuticornis-group (Kotov, 2007b). The endemic genus Dumontiellus Smirnov, 2007 is another example of a South African rock-pool endemic from high altitudes, and so is Pleuroxus carolinae (Smirnov, 2007;Smirnov et al, 2006).…”

“…Stacked photographs of A. capensis were made using a mounted digital camera and compiled with HeliconFocus™ software. For the system of seta enumeration, see previous papers (Kotov, 2007a(Kotov, , 2007b(Kotov, , 2009Bekker et al, 2012). The homologies of different limb parts of the Anomopoda are explained in Smirnov and Kotov (2010).…”

The Morphological Radiation of Setae in the Cladocera (Crustacea) and Their Potential for Morphogenesis

“…12I). At the same time, in other Macrothrix species with known morphology (KOTOV, 1999b(KOTOV, , 2007b Fig. 11G) no such transformation of the form of the posterior setae of thoracic limbs takes place.…”

“…A tendency for reduction of the number of posterior setae is strong in the chydorid line. In Bosmina, Ophryoxus and Macrothrix, the series of posterior setae is incomplete; only remnants of this series are present (e.g., see KOTOV, 1999bKOTOV, , 2007b, see also Fig. 10A, C).…”