Anastasiia A. Saulenko

Four species of tardigrades have been found in the meiofauna communities of the seagrass meadows and adjacent areas off the coast of Vietnam. For two of them, Batillipes binhdinhicus sp. nov. and Batillipes ampullus sp. nov., integrative descriptions are presented. Batillipes binhdinhicus sp. nov. belongs to the B1 subgroup of species by having toe 3 shorter than toe 4 on legs IV, while Batillipes ampullus sp. nov. with toes 3 and 4 on legs IV of equal length belongs to the A group of species. Batillipes binhdinhicus sp. nov. can be distinguished from all previously described species by a set of features: very long cephalic cirri and leg sensory spines, both with swollen tips, presence of a single pair of conical lateral body projections between all pairs of legs and simple triangular caudal appendage. The distinctive features for Batillipes ampullus sp. nov. are short sensory organs on the fourth pair of legs, which consists of two parts and have swollen tips with a tuft of additional sensory filaments that are structurally similar to those found on the cephalic appendages. In addition, Batillipes ampullus sp. nov. does not have noticeable lateral body projections between the legs, and the body ends in a semi-circular tail appendage. Based on the obtained data on the nucleotide sequences of 18S rDNA and 28S rDNA, the distinction between the new species was confirmed.

Hadal trenches, some of the Earth’s least explored and understood environments, have long been proposed to harbour chemosynthesis-based communities^1,2. Despite increasing attention, actual documentation of such communities has been exceptionally rare^3,4. Here we report the discovery of the deepest and the most extensive chemosynthesis-based communities known to exist on Earth during an expedition to the Kuril–Kamchatka Trench and the western Aleutian Trench using the manned submersible Fendouzhe. The communities dominated by siboglinid Polychaeta and Bivalvia span a distance of 2,500 km at depths from 5,800 m to 9,533 m. These communities are sustained by hydrogen sulfide-rich and methane-rich fluids that are transported along faults traversing deep sediment layers in trenches, where methane is produced microbially from deposited organic matter, as indicated by isotopic analysis. Given geological similarities with other hadal trenches, such chemosynthesis-based communities might be more widespread than previously anticipated. These findings challenge current models of life at extreme limits and carbon cycling in the deep ocean.

Three deep-sea tardigrade species were identified from the sediment samples collected during the four German–Russian joint deep-sea cruises that were conducted in the North-Western Pacific: Coronarctus sonne sp. nov., Moebjergarctus okhotensis sp. nov., and Angursa cf. bicuspis. Specimens of those species were collected at depths between 1700 and 5410 m. The new species Coronarctus sonne sp. nov. belongs to the Cor. tenellus group of species on the basis of morphological traits such as the short cephalic appendages and heteromorphic claws. The structure of the secondary clavae and two points, with an accessory point and a primary point simultaneously on the internal and external claws on legs IV, are significant characteristics distinguishing Coronarctus sonne sp. nov. from other described species. Moebjergarctus okhotensis sp. nov. is characterized by having cephalic cirri with the long smooth portion of the scapus and annulated scapus only in the basal portion, the structure of the male and female reproductive system, and differences in the sizes of some structures compared to the other described species. An analysis of the results of four deep-sea expeditions indicates a patchy distribution of tardigrades in the North-Western Pacific.

Oloncholaimus piipi gen. et sp. nov. is described from Piip submarine volcano, the Bering Sea. Oloncholaimus gen. nov. shows all main characters of Oncholaiminae: females monodelphic-prodelphic with antidromously reflexed ovary, three teeth with left ventrosublateral the largest, oncholaimoid type of Demanian system. New genus can be differentiated from all other genera of the family Oncholaimidae by the complex shape of dorsal and right ventrosublateral teeth with apical antler-shaped extension. Oloncholaimus piipi sp. nov. has large body (5960–7045 μm), six outer labial and four cephalic setae equal in size (5–7 μm), equal spicules (110–131 μm long) without gubernaculum, and complex precloacal supplementary organ composed of 8–9 cylindrical processes.