Hypsibius, Ehrenberg, 1848

Bartels, Paul J., Fontoura, Paulo & Nelson, Diane R., 2018, Marine tardigrades of the Bahamas with the description of two new species and updated keys to the species of Anisonyches and Archechiniscus, Zootaxa 4420 (1), pp. 43-70 : 64-65

Hypsibius sp.

Material examined: One specimen from site 1, body length 171 µm.

Remarks: This single specimen is poorly preserved and oriented so that an adequate description is not

possible. But it is remarkable in that only a very small number of marine eutardigrades are known. The genus Halobiotus Kristensen, 1982 is secondarily adapted to saltwater environments in northern latitudes, as is, apparently, Thulinius itoi Tsurusaki, 1980 . All were described from intertidal or supralittoral sand. Our specimen was found in sand at 3 m depth, over 2000 m from the nearest shore. Is it a truly marine species or a terrestrial species that was an “accidental” in these samples? The distance from shore might suggest the former hypothesis, while the lone occurrence supports the latter. The specimen has a granulated cuticle without gibbosities, no visible eyes, Hypsibius - type claws with thick primary branches and well-developed accessory points, light refracting areas at the base of primary branches of all claws, lack of claw lunules, and a pharynx with two small macroplacoids (the first pear-shaped and larger than the second) and a minute roundish microplacoid/septula. Together with some morphometric characters, this does not match any currently known Hypsibius species. It seems to us improbable that an accidental terrestrial specimen would also be a species never before encountered. Further sampling is needed to resolve this intriguing question.