A new gastrotrich species, Musellifer leasiae sp. nov., is described from the west coast of the Antarctic Peninsula. The species is recognised by its considerable size, up to 415 μm, and by its conspicuous three-lobed, keeled head scales. Besides the new species, the genus Musellifer accommodates five additional species known from the Mediterranean Sea, the Black Sea, the Central-West Atlantic, the Northeast Atlantic, and the Northeast Pacific, and from depths ranging from sublittoral to 5.485 m depth. A representative of Musellifer has previously been reported from Antarctica, but M. leasiae sp. nov. represents the first formally described Muselliferidae species from the Southern Hemisphere, and from the polar regions.
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With only three named species, Antarctica is the continent with the least explored kinorhynch biodiversity. The present contribution provides the most comprehensive study of Antarctic kinorhynchs collected along the coast of the West Antarctic Peninsula. Quantitative samples were collected in three regions along the Peninsula: in Andvord Bay Fjord at the Danco Coast, in the Gerlache Strait, and on the open continental shelf west of the Peninsula. Comparison of the sampling areas suggests that the highest kinorhynch abundance was in the Gerlache Strait, where kinorhynchs were over six times more abundant than in Andvord Bay. Lowest abundance was on the open shelf, where the abundance was four times lower than in Andvord Bay. Among all examined specimens 98% were found in the top 4 cm of the sediment. All adult kinorhynchs were identified, and the study revealed the presence of the known Antarctic species Polacanthoderes shiraseae and at least seven species new to science: Condyloderes notios sp. nov., Polacanthoderes grzelakae sp. nov., Echinoderes ahlfeldae sp. nov., E. nataliae sp. nov., E. kathleenhannae sp. nov., E. antarcticus sp. nov., and E. crux sp. nov. In addition to the five new species of Echinoderes, two potentially known species are reported. Echinoderes aff. angustus shows close resemblance to the Arctic E. angustus, and the specimens only differed by their lack of a midventral fissure in segment 2, present in Arctic specimens of E. angustus only. A detailed examination of the E. angustus type material revealed new diagnostic details for the species, i.e., a complete mapping of sensory spots, presence of a middorsal protuberance between segments 10 and 11, and a tergal division of segment 11. Another unidentified species, Echinoderes aff. beringiensis/romanoi/xalkutaat, showed such close resemblance to three congeners that further studies are needed to identify clear diagnostic characters for the species, or alternatively clarify whether they should be synonymised. The comparisons prompted by the two unidentified species led to the suggestion of a new species group, the Echinoderes remanei species group, including E. remanei, E. angustus, E. beringiensis, E. cernunnos, E. drogoni, E. galadrielae, E. obtuspinosus, E. quasae, E. pennaki, E. romanoi, and E. xalkutaat. In addition, the Echinoderes aragorni species group is proposed, including the New Zealand species E. aragorni and the new species E. crux.
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