Revision of the phylogeny of Placididea (Stramenopiles): Molecular and morphological diversity of novel placidid protists from extreme aquatic environments

Recent studies suggested that the diversity of microbial eukaryotes in hypersaline environments is widely underestimated. Placidids are a group of heterotrophic stramenopile flagellates that are frequently found in these environments, but up to now only very few species were isolated and fully described, mostly from marine or brackish water sites. In this study, we extend the known diversity of Placididea by three new genera (Allegra, Haloplacidia, and Placilonga) compromising nine new species, isolated from athalassic, mostly hypersaline environments (Allegra dunaii, Allegra atacamiensis, Allegra hypersalina, Haloplacidia cosmopolita, Suigetsumonas keniensis) and marine waters (Placilonga atlantica, Placidia azorensis, Placidia abyssalis, Wobblia pacifica) including a description of their morphology and molecular phylogeny. In total, 36 strains were comparatively analysed. Studies from athalassic waters revealed an especially high number of different genotypes. A multigene analysis based on a ten genes dataset revealed a clear separation into marine, athalassic and brackish water clades. Several representatives were found to cope with hypersaline conditions from 20 to 250 PSU, even up to 284 PSU, suggesting that they may form a halotolerant group.