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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RBINS Staff Publications 2018
Mitochondrial DNA hyperdiversity is primarily caused by high mutation rates (µ) and has potential implications for mitogenome architecture and evolution. In the hyperdiverse mtDNA of Melarhaphe neritoides (Gastropoda: Littorinidae), high mutational pressure generates unusually large amounts of synonymous variation, which is expected to (1) promote changes in synonymous codon usage, (2) reflect selection at synonymous sites, (3) increase mtDNA recombination and gene rearrangement, and (4) be correlated with high mtDNA substitution rates. The mitogenome of M. neritoides was sequenced, compared to closely related littorinids and put in the phylogenetic context of Caenogastropoda, to assess the influence of mtDNA hyperdiversity and high µ on gene content and gene order. Most mitogenome features are in line with the trend in Mollusca, except for the atypical secondary structure of the methionine transfer RNA lacking the TΨC-loop. Therefore, mtDNA hyperdiversity and high µ in M. neritoides do not seem to affect its mitogenome architecture. Synonymous sites are under positive selection, which adds to the growing evidence of non-neutral evolution at synonymous sites. Under such non-neutrality, substitution rate involves neutral and non-neutral substitutions, and high µ is not necessarily associated with high substitution rate, thus explaining that, unlike high µ, a high substitution rate is associated with gene order rearrangement.
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