Mopsechiniscus franciscae, a new species of a rare genus of Tardigrada from continental Antarctica

Despite the importance and regular occurrence of tardigrades in the Antarctic terrestrial ecosystem, taxonomic studies of, in particular, continental Antarctica species have advanced very slowly. During a large survey to study tardigrade biodiversity along the Victoria Land coastal line, a new species was found belonging to the rare heterotardigrade genus Mopsechiniscus. The new species Mopsechiniscus franciscae is described using an integrative taxonomy approach, combining morphological description (with light and electron microscopy techniques) and molecular characterisation (analysing portions of the 18S and 28S genes). The new species differed from other congeners by clear morphological characters related to shape and sculpture of cuticular plates, presence of papillae on legs, and length and number of body filaments. The results of the combined (18S+28S) phylogenetic analyses (Bayesian and Maximum Likelihood) on Echiniscoidea indicate two main lineages: one incorporating the genus Echiniscoides (Echiniscoididae) and the other the current data on Echiniscidae and Oreellidae genera. Although the resolution of relationships within the latter line is not clear, there is a well defined evolutionary line for Mopsechiniscus. The addition of continental Antarctic M. franciscae sp. nov. to the genus broadened the distributional range of Mopsechiniscus southwards and supported the hypothesis that the genus represents a Gondwanan faunal element. Our report of a new Antarctic species, belonging to this rare heterotardigrade genus, increases our knowledge of the underreported terrestrial meiofaunal communities within continental Antarctica.