Morphology and multi-gene phylogeny of Rubrioxytricha hasllaensis n. sp. (Ciliophora, Spirotrichea) from South Korea.

The morphology and multi-gene phylogeny of Rubrioxytricha hasllaensis n. sp., a non-oxytrichid dorsomarginalian ciliate discovered in a brackish water habitat in South Korea, were investigated. The new species is characterized by a body size of 125-145 × 30-40 μm in vivo, colorless cytoplasm, yellow cortical granules, 30-36 adoral membranelles, 25-35 left and 25-38 right marginal cirri, a single caudal cirrus, and undulating membranes distinctly curved leftward. In phylogenetic analyses based on 18S rRNA gene sequences, the new species clusters with other Rubrioxytricha species, forming a monophyletic clade that groups with members of the genera Polystichothrix, Pseudogastrostyla, Pseudocyrtohymena, and Pseudocyrtohymenides. In phylogenetic analyses using concatenated 18S-ITS1-5.8S-ITS2 and partial 28S rRNA gene sequences, newly obtained sequences from Rubrioxytricha, Pseudocyrtohymena, and Pseudocyrtohymenides form a sister clade to the assemblage of soft-bodied hypotrichs possessing dorsal kinety fragmentation. In addition to identifying morphological apomorphies shared by Rubrioxytricha and its phylogenetically related genera, including the absence of dorsal kinety fragmentation, a reduced number of caudal cirri, and the presence of a bipolar dorsomarginal kinety, new generic characters are introduced for dorsomarginalian hypotrichs and used to improve the diagnosis of the genus Rubrioxytricha.