Molecular phylogeny and taxonomy of three anaerobic plagiopyleans (Alveolata: Ciliophora), retrieved from two geographically distant localities in Asia and North America

Anaerobic ciliates are key organisms for studying adaptations to an anaerobic lifestyle, the evolution of eukaryotic cell organelles, mechanisms of energy metabolism, and symbiosis with prokaryotes; however, the biodiversity of their marine representatives remains poorly known. In this study, three species of ciliates belonging to the class Plagiopylea, i.e. Trimyema foissneri sp. nov., Plagiopyla rariseta sp. nov., and Plagiopyla frontata, collected from various marine anoxic habitats from two geographically distant continents, Asia and North America, were investigated using morphological and molecular methods. Trimyema foissneri can be recognized by three complete somatic ciliary girdles, special arrangement of kinetosomes near the anterior end of the oral kineties, and the presence of a ventrolateral fragment. Plagiopyla rariseta is distinguished by sparse cilia on the frontal region and particular orientation of the buccal cavity. Plagiopyla frontata is newly recorded and is redescribed in detail and redefined based on new populations. Phylogenetic analyses based on the small subunit ribosomal ribonucleic acid (SSU rRNA) gene supported the generic assignment of the three species and corroborated the monophyly of the families Trimyemidae and Plagiopylidae. An improved key to the identification of the valid species of genus Trimyema is also supplied.

Automated summary

This study investigated three species of anaerobic ciliates collected from marine anoxic habitats in Asia and North America, using morphological and molecular methods. The species were identified as Trimyema foissneri, Plagiopyla rariseta, and Plagiopyla frontata. Trimyema foissneri is characterized by its somatic ciliary girdles, arrangement of kinetosomes, and ventrolateral fragment. Plagiopyla rariseta has sparse cilia on the frontal region and a specific orientation of the buccal cavity. Plagiopyla frontata is redescribed in detail. Phylogenetic analysis supported the generic assignment of the three species and confirmed the monophyly of the families Trimyemidae and Plagiopylidae. An improved key for the identification of Trimyema species is provided.