Comparative analyses of Bertolanius species (Eohypsibiidae; Eutardigrada) with the description of Bertolaniusbirnae sp. nov. from northern polar regions

Species of the genus Bertolanius (Eohypsibiidae, Eohypsibioidea) are morphologically very similar and can be distinguished by only minute differences. During faunal surveys in Arctic areas (Disko I., Greenland; Uummannaq, Greenland; Abisko, Sweden), the four species Bertolanius nebulosus, Bertolanius smreczynskii, Bertolanius weglarskae and Bertolanius birnae sp. nov. were found. Bertolanius nebulosus and Bertolaniussmreczynskii have been compared with their paratypes, and type material of other species of Bertolanius has been considered for comparison within the genus. Bertolaniusbirnae sp. nov. possesses a unique combination of characters (i.e., an evident anterior band of teeth, the median ridge of the buccal armature consisting of two large teeth instead of one, absence of eyes, and eggs with conical processes without areolation around their bases) that is not seen in any other species in the genus, though these characters may be present in other combinations within the genus. Our revision and analytical comparison among these Bertolanius species adds new and important information on claw, buccal armature, egg surface morphologies as well as the encystment process of the species. We also provide a taxonomic key to aid the identification of Bertolanius species. The new discoveries of Bertolanius species from northern polar regions further support the hypothesis that the distribution of Eohypsibioidea is restricted to the Holarctic in the Arctic and Periarctic areas, or in alpine areas between 550 and 2400 m a.s.l. of more temperate regions.