Expanding Acutuncus: Phylogenetics and morphological analyses reveal a considerably wider distribution for this tardigrade genus

The tardigrade genus Acutuncus has been long thought to be an Antarctic endemism, well adapted to this harsh environment. The Antarctic endemicity of Acutuncus was recently dispelled with the description of Acutuncus mariae Zawierucha, 2020 found in the Svalbard archipelago. The integrated analyses on two newly found Acutuncus populations from UK and Italy, and a population of Acutuncus antarcticus found close to its type locality allowed us to expand the climatic and geographic range of the genus Acutuncus. These findings also allowed us to re-evaluate the morphological diagnoses of Acutuncus and accommodate it in the newly proposed monotypic family Acutuncidae fam. nov. Two new Acutuncus species morpho-groups are instituted based on eggs morphology: one (Acutuncus antarcticus morphogroup) including the Antarctic Acutuncus taxa characterized by eggs with long pillars within the chorion and eggs laid freely to the environment, the other (Acutuncus mariae morphogroup) including the European species, characterized by eggs with short pillars within the chorion and eggs laid in the exuvium. Finally, we describe two new Acutuncus species from Europe: Acutuncus mecnuffi sp. nov. and Acutuncus giovanniniae sp. nov.

Automated summary

The Antarctic endemicity of the Acutuncus genus was refuted with the discovery of Acutuncus mariae Zawierucha, 2020 in the Svalbard archipelago. Through integrated analysis of Acutuncus populations from the UK and Italy, as well as a population of Acutuncus antarcticus near its type locality, the climatic and geographic range of the Acutuncus genus was expanded. These findings led to the re-evaluation of Acutuncus morphological diagnoses and its classification in the newly proposed monotypic family Acutuncidae fam. nov. Two new Acutuncus species were described from Europe: Acutuncus mecnuffi sp. nov. and Acutuncus giovanniniae sp. nov.