0065-1583 Jagiellonian University in Kraków Constraints on Phylogenetic Interrelationships among Four Free-living Litostomatean Lineages Inferred from 18S rRNA gene-ITS Region sequences and Secondary Structure of the ITS2 molecule Rajter Ľubomír author Vďačný Peter author Phycology, Faculty of Biology, University of Duisburg-Essen, Essen, Germany Eukaryotic Microbiology, Faculty of Biology, University of Duisburg-Essen, Essen, Germany Comenius University, Department of Zoology, Bratislava, Slovakia Correspondence to: Ľubomír Rajter Correspondence to: Peter Vďačný 14 12 2017 Volume 56, Issue 4 2017 255 281 Copyright © 2017 2017 <p>We investigated interrelationships between four free-living litostomatean lineages, using 18S rRNA gene and ITS region sequences as well as the secondary structure of the ITS2 molecules. Our phylogenetic analyses confirmed the deep split of free-living litostomateans into Rhynchostomatia and Haptoria represented here by Haptorida, Pleurostomatida, and Spathidiida. This bifurcation is also corroborated by the signature of the rhynchostomatian and haptorian ITS2 molecules. Specifically, the consensus stems of helices II and III are longer by one base pair in Rhynchostomatia, while the terminal loops of both helices are longer by one or two nucleotide/-s in Haptoria. A close relationship of Pleurostomatida and Haptorida is favored by quartet likelihood-mapping and supported by a 5’-AG vs. CU-3’ motif in the variable part of helix II and by two morphological apomorphies, i.e., meridionally extending somatic kineties and a non-three-rowed dorsal brush. Although monophyletic origin of Spathidiida is poorly supported in phylogenetic trees, the unique motif 5’-GA vs. UC-3’ present in the consensus helix II stem could be an important molecular synapomorphy of spathidiids, apart from the ancestrally anteriorly curved somatic kineties and the three-rowed dorsal brush. The peculiar family Pseudoholophryidae has very likely found its phylogenetic home among spathidiids, as an early branching lineage.</p> 1 Alfaro M. E., Zoller S., Lutzoni F. (2003) Bayes or bootstrap? A simulation study comparing the performance of Bayesian Markov Chain Monte Carlo sampling and bootstrapping in assessing phylogenetic confidence. Mol. Biol. Evol. 20: 255–266 2 André E. (1915) Recherches sur la faine pélagique du Léman et description de neoveaux genres d’infusoires. Revue Suisse Zool. 22: 179–193 3 Berger H., Foissner W., Adam H. (1984). Taxonomie, Biometrie und Morphogenese einiger terricoler Ciliaten (Protozoa: Ciliophora). Zool. Jahrb. 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