To date, only one mitogenome from an Antarctic amphipod has been published. Here, novel complete mitochondrial genomes (mitogenomes) of two morphospecies are assembled, namely, Charcotia amundseni and Eusirus giganteus. For the latter species, we have assembled two mitogenomes from different genetic clades of this species. The lengths of Eusirus and Charcotia mitogenomes range from 15,534 to 15,619 base pairs and their mitogenomes are composed of 13 protein coding genes, 22 transfer RNAs, 2 ribosomal RNAs, and 1 putative control region CR. Some tRNAs display aberrant structures suggesting that minimalization is also ongoing in amphipod mitogenomes. The novel mitogenomes of the two Antarctic species have features distinguishing them from other amphipod mitogenomes such as a lower AT-richness in the whole mitogenomes and a negative GC- skew in both strands of protein coding genes. The genetically most variable mitochondrial regions of amphipods are nad6 and atp8, while cox1 shows low nucleotide diversity among closely and more distantly related species. In comparison to the pancrustacean mitochondrial ground pattern, E. giganteus shows a translocation of the nad1 gene, while cytb and nad6 genes are translocated in C. amundseni. Phylogenetic analysis based on mitogenomes illustrates that Eusirus and Charcotia cluster together with other species belonging to the same amphipod superfamilies. In the absence of reference nuclear genomes, mitogenomes can be useful to develop markers for studying population genetics or evolutionary relationships at higher taxonomic levels.
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Pseudocypretta amor sp. nov. (named after the carapace spots resembling the word “Love”) is here described from all-female populations from the four major floodplains in Brazil. The new species is compared to the other two know species in the genus, P. maculata Klie (1932), the type species, and P. lineata Ma and Yu (2020). As the latter two species are thus far found exclusively in South East Asia and China, respectively, the present extension of the area of the genus to South America is considerable. Several morphological characters in this genus and species are discussed, especially the presence of marginal septa in the valves, the candonid type T3 with 3rd and 4th segment separated (candonid type) and the caudal ramus which is reduced to a flagellum (cypridopsine type) or is fully absent. Based on the combination of these and other characters, the genus Pseudocypretta is here transferred from the Cyprettinae to the tribe Cyprettadopsini in the Cypridopsinae, as it is closely related to the genus Cyprettadopsis Savatenalinton, 2020. The presence of the candonid type T3 in Cyprididae and Notodromadidae, where the T3 generally has a pincer-shaped tip by the fusion of the 3rd and the 4th segment, is further discussed.
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