Tardigrades of the genus Halobiotus (Eutardigrada, Isohypsibioidea) inhabiting Arctic seas – new taxonomic and biological data

In this paper we present the results of taxonomic and ecological investigation of several populations of marine tardigrades of the genus Halobiotus inhabiting the seas of Russian Arctic. We studied representatives of the genus Halobiotus collected from three localities of the White Sea, from the Barents Sea and from the Laptev Sea. Morphological analysis was performed using the methods of light and scanning electron microscopy, and supplemented with statistical analysis of the morphometric data. For the comparative genetic analysis, we obtained data on mitochondrial COI gene and on 18S rRNA, 28rRNA and ITS-2 sequences. Our study revealed the presence of two species, clearly differentiated both morphologically and genetically in the fauna of Arctic seas of Russia. Comparison of our specimens with the available type material of the previously described Halobiotus species and the obtained gene sequences with those deposited in GenBank made it possible to attribute the White Sea and the Barents Sea populations to the species Halobiotus crispae , while the Laptev Sea population was recognized as belonging to Halobiotus arcturulius . We provide here emended morphological descriptions for both species based on the in-depth study of the obtained material together with the type specimens of both species. In our opinion, the genus Halobiotus currently includes only two adequately described species, other species of this genus should be considered nomina inquirendae. We provide a new diagnosis for the family Halobiotidae based on the new data, and specify taxonomic position of the species Isohypsibius occultus as Grevenius occultus comb. nov. We also provide new biological data for the Halobiotus spp. populations from the Barents Sea and the Laptev Sea.