It is demonstrated here that Charcotia Chevreux, 1906 (Amphipoda) has priority over Charcotia Vayssière, 1906 (Gastropoda), and that Waldeckia Chevreux, 1906 has to be treated as an invalid objective junior synonym of Charcotia Chevreux, 1906. An analysis of a part of the mitochondrial COI gene of Charcotia indicates that Charcotia obesa sensu lato, consists of two genetically distant clades that fulfil the criteria of genetic species. Each genetic clade corresponds to a different morphotype. The first one has a low triangular protrusion on the dorsal border of urosomite 1, a strong tooth on epimeron 3, and the posterodistal corner of the basis of pereiopod 7 is regularly rounded. It agrees with the original description of Charcotia obesa Chevreux, 1906. The second one has a protrusion of urosomite 1 prolongated by a sharp and usually long denticle, a small tooth on epimeron 3, and the posterodistal corner of the basis of pereiopod 7 is bluntly angular. The second form is treated herein as a new species, Charcotia amundseni sp. nov., which is described in detail. While the bathymetric distribution of the two Antarctic Charcotia species overlaps (0–300 m for C. obesa and 7–1200 m for C. amundseni sp. nov.), C. obesa largely predominates at depths of less than 150 m, while Charcotia amundseni sp. nov. predominates at greater depths. Both species are widely distributed and presumably circum-Antarctic.
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Cladogenesis is often driven by the interplay of dispersal and vicariance. The importance of long-distance dispersal in biogeography and speciation is increasingly recognised, but still ill-understood. Here, we study faunal interconnectivity between four large Brazilian floodplains, namely the Amazon, Araguaia, Pantanal (on Paraguay River) and Upper Paraná River floodplains, investigating a species complex of the non-marine ostracod genus Strandesia. We use DNA sequence data from the mitochondrial COI and the nuclear Elongation Factor 1 alpha genes to construct molecular phylogenies and minimum spanning networks, to identify genetic species, analyse biogeographic histories and provide preliminary age estimates of this species complex. The Strandesia species complex includes five morphological and eleven genetic species, which doubles the known diversity in this lineage. The evolutionary history of this species complex appears to comprise sequences of dispersal and vicariance events. Faunal and genetic patterns of connectivity between floodplains in some genetic species are mirrored in modern hydrological connections. This could explain why we find evidence for (aquatic) long-distance dispersal between floodplains, thousands of kilometres apart. Our phylogenetic reconstructions seem to mostly indicate recent dispersal and vicariance events, but the evolution of the present Strandesia species complex could span up to 25 Myr, which by far exceeds the age of the floodplains and the rivers in their current forms.
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