Morphology and Molecular Phylogeny of Pseudocyrtohymena koreana n. g., n. sp. and Antarctic Neokeronopsis asiatica Foissner et al., 2010 (Ciliophora,Sporadotrichida), with a Brief Discussion of the Cyrtohymena Undulating Membranes Pattern

We discovered a new brackish water oxytrichid Pseudocyrtohymena koreana n. g., n. sp. in South Korea and investigated the new species on the basis of morphology, ontogenesis, and 18S rRNA gene sequences. The new genus has the 18 frontal‐ventral‐transverse cirri of typical oxytrichids with flexible body, cortical granules, Cyrtohymena undulating membranes (UM), and one left and one right marginal cirral row. Ontogenesis of the new species indicated that dorsal kinety anlage 3 stretches within the parental row without any fragmentations (Urosomoida pattern) and exclusively forms all caudal cirri. The new genus is morphologically similar to Cyrtohymena Foissner, 1989, but has the following distinctive features: (i) caudal cirri absent in dorsal kineties 1 and 2 (vs. present in Cyrtohymena); and (ii) dorsal kinety 3 nonfragmented (vs. fragmented in Cyrtohymena). Further, we collected an additional species Neokeronopsis asiatica Foissner et al. 2010, from King George Island, Antarctica, and the species shares the morphology of UM with Cyrtohymena. Herein, we describe the previously unidentified characteristics of N. asiatica (i.e., cortical granules, body flexibility, contractile vacuole, and 18S rRNA gene sequence). In addition, we obtained two 18S rRNA gene sequences from Cyrtohymena muscorum and Parasterkiella thompsoni to expand samples for phylogenetic analysis. Our 18S rRNA gene tree supports the hypothesis that the Cyrtohymena UM pattern might have evolved several times in hypotrichs (e.g., Neokeronopsidae, Oxytrichinae, and Stylonychinae).