Characterizing the divisional mode of anaerobic genus Plagiopyla (Alveolata, Ciliophora, Plagiopylea), with notes on morphology and phylogeny of the type and one common species.

Although their ecological and evolutionary significance has been demonstrated very recently, ciliates belonging to the anaerobic class Plagiopylea have never been investigated adequately in terms of diversity, phylogeny, and in particular ontogeny. Here, morphological, ontogenetic and molecular characterization are documented for the type species Plagiopyla nasuta and one common form P. frontata, by the use of state-of-art techniques for ciliates. The genus Plagiopyla was first found to have a stable divisional mode, and showed the following characteristics: (1) Holotelokinetal stomatogenesis, i.e., all somatic kineties are involved in the development of the opisthe's oral apparatus. (2) Several parental kinetal rows near striated band proliferate, and form the anlagen of compact kinetids (CK) and internal buccal kinetids (IBK) in the opisthe. (3) Parental oral lip kineties and CK dedifferentiate and reorganize in situ, and parental IBK seem to be retained by the proter. Phylogenetic analyses corroborate the monophyly of the family Plagiopylidae. The newly obtained sequences of P. frontata and P. nasuta cluster together with sequences of other populations of each species with high to full support. Additionally, the IBK, a conserved but long-overlooked component of the oral apparatus, are revealed for the first time in the genus Plagiopyla. The origin, structure and position of CK together suggest that the structure might be homologous to brosse, a characteristic feature of the class Prostomatea.