Morphology and Phylogeny of Two Novel Pleurostomatids (Ciliophora, Litostomatea), Establishing a New Genus.

Pleurostomatida Schewiakoff, 1896 is a cosmopolitan order of ciliates. In the present study, we investigated two new pleurostomatid species, Apolitonotus lynni gen. et sp. nov. and Protolitonotus clampi sp. nov., with state-of-the-art methods. Apolitonotus lynni lacks its oral extrusomes and its right kineties form an anterior semi-suture near the dorsal margin. Based on these two features, the new genus Apolitonotus was established within the Protolitonotidae Wu et al., 2017. Protolitonotus clampi differs from its congeners by its size of 80-130 × 15-30 μm, 4-6 left, and 9-11 right kineties, extrusomes arranged along the oral slit, and two macronuclear nodules. Because Litonotus antarcticus possesses an anterior semi-suture and oral extrusomes, it was transferred to the genus Protolitonotus, becoming P. antarctius comb. nov. (basionym Litonotus antarcticus Song and Wilbert, 2002). Phylogenetic analyses based on SSU rDNA sequences suggest a sister group relationship of P. clampi and the family Kentrophyllidae, and A. lynni is adelphotaxon to Litonotus gracilis, both within the order Pleurostomatida. Based on the new findings, an improved diagnosis for Protolitonotus was also provided.