Discovery of a new Kinorhyncha species from the uncharted South Orkney Trench (Southern Ocean)

The knowledge about the deep-sea Kinorhyncha community has increased considerably in recent years. However, the records of kinorhynchs inhabiting hadal depths are still extremely limited. In the present study, we describe a new species of Echinoderes discovered from the South Orkney Trench, Southern Ocean. Echinoderes australis sp. nov. is characterized by the presence of middorsal acicular spines on segments 4-8 and lateroventral ones on segments 6-9, and tubes in lateroventral position on segment 5, in lateral accessory position on segment 8, and in laterodorsal position on segment 10. Additionally, the new species has conspicuous papillary flaps on segments 8-9. Among its morphological characteristics, the increase in length of the middorsal spine of segment 8 and lateroventral spines of segment 9 in relation to those of the previous segments are striking features, showing a whip-like appearance. E. australis sp. nov. Becomes the third hadal species of the phylum. In addition, we provide morphological information on the two other species found in the trench. Finally, we study in detail the diversity and distribution patterns of the Kinorhyncha of the South Orkney Trench, addressing aspects such as species richness, abundance, number of adults versus juveniles and the effect of bathymetry on the community composition.