Paramecium (ciliophora, protista). Taxonomy and phylogenetic relationships

The relationships between thirteen Paramecium species were investigated using a number of biological, morphometric, and molecular-biological (SS rRNA gene sequences) characters. Analysis of sequences was also applied for Frontonia, Lembadion, and Urocentrum species. The similar results were obtained by using various methods. The genus Paramecium is found to be monophyletic and along with other peniculines (Lembadion and Frontonia) it composes Peniculia subclass of the class Oligohymenophorea. The data obtained support no variant of the Paramecium classification (2 subgroups according to Woodruff and 3 subgroups in Jankowsky's taxonomy) suggested earlier. Paramecium bursaria, P. duboscqui, and P. putrinum are the most ancient and divergent species within the genus. Part of the woodruffi subgroup (P. woodruffi, P. nephridiatum and P. calkinsi) and the aurelia subgroup (P. aurelia complex, P. jenningsi, P. caudatum, and P. multimicronucleatum) from two monophyletic clusters and can be considered as subgenera. The taxonomy of Paramecium should be reconstructed. The subclass Peniculia should be divided into two orders - Urocentrida and Peniculida.