A new “flagship” ciliate, Pseudostylonychia obliquocaudata n. gen., n. sp. (Ciliophora, Hypotricha), from South Korea

The morphology, ontogenesis, and molecular phylogeny of a new ciliate, Pseudostylonychia obliquocaudata n. gen., n. sp., discovered in a semiterrestrial habitat in South Korea, were investigated. The new species is characterized by an obovate or triangular body with pointed posterior end. The caudal area is distinctly obliquely truncated rightwards. Pseudostylonychia n. gen. is established and characterized by the obovate or triangular body, Stylonychia-like infraciliature and macronuclear pattern, and undulating membranes in Laurentiella pattern. It is also characterized by the involvement of cirri III/2 and IV/3 in primordia formation. SEM investigations show that the resting cyst has high, spirally arranged ridges. Phylogenetic analyses based on SSU rRNA gene sequences show that the new species is placed as a sister to the clade containing sequences of Stylonychia mytilus complex, Stylonychia (Metastylonychia), and Coniculostomum. Furthermore, Stylonychia koreana Kumar et al., 2016 nov. stat. is raised to species level based on the differences in the cyst morphology between the two subspecies of S. ammermanni. Also, Metastylonychia Kumar and Foissner, 2017 nov. stat. is raised to genus rank based on the new molecular data and the morphological and ontogenetic differences to Coniculostomum and Stylonychia.