Multiple Euryhaline Lineages of Centrohelids (Haptista: Centroplasthelida) in Inland Saline Waters Revealed with...

The diversity of centrohelids in inland saline waters was studied with metabarcoding for the first time. The fragment of V6-V7 regions of 18S rDNA was sequenced with newly designed primers. Obtained OTUs were identified with molecular phylogenetic analysis and comparison of the signatures in 39es9 hairpin of V7. The obtained data included some OTUs, which could be attributed to four described species, but the majority belonged to previously established or novel environmental clades. Along with some presumably marine/brackish clades and freshwater/low salinity (0-2 ppt) clades, seven presumable species demonstrating broad (from 1-2 up to 78 ppt) salinity tolerance were detected. A number of OTUs belonged to Raphidocystis contractilis, which is known from three independent findings in brackish habitats only. Thus, it was assumed that this species is stenohaline and specifically adapted to salinity 5-15 ppt. The high level of salinity tolerance was suggested for centrohelids before based on morphology, which was used to justify their cosmopolitan distribution. Later these views were criticized based on environmental sequencing, but the results of the current survey indicate, that at least some species are present at salinities from almost freshwater (1-2 ppt) to twice oceanic (78 ppt) and are presumably capable of overcoming oceanic salinity barriers for their distribution.