Phylogeny of the anaerobic ciliate genus (Protista: Ciliophora: Plagiopylea), including the description of three novel species and a brief revision of the genus.

Anaerobic protists in general, and ciliates in particular, are important components of anoxic or hypoxic environments, however, their diversity remains underestimated. is a poorly studied genus that is distributed worldwide and is commonly found in anaerobic environments. In the present study, the taxonomy and phylogeny of three new species, namely sp. nov., sp. nov. and sp. nov., collected from China, were investigated based on microscopic observations and SSU rRNA gene sequencing methods. sp. nov. is diagnosed mainly by having a relatively large body size, a crescent-shaped oral opening, numerous slender extrusomes, one suture on the ventral side and two on the dorsal side, and a buccal cavity that occupies the anterior third of the cell. sp. nov. closely resembles but differs mainly by its oral opening being located closer to the anterior cell margin and its spindle-shaped extrusomes. sp. nov. is a freshwater species that can be recognized by its shallow buccal cavity, sparsely distributed rod-shaped extrusomes, and having 68-79 monokinetidal somatic kineties that form sutures on both sides of the body. Phylogenetic analyses based on small subunit ribosomal RNA (SSU rRNA) gene sequence data support the monophyly of the family Sonderiidae, however, is paraphyletic. The genus is briefly revised and a key to the identification of species belonging to this genus is supplied.