Molecular phylogeny and taxonomy of three anaerobic ciliates including Bothrostoma aporobustum nov. spec. (Ciliophora, Metopida)

Abstract

The order Metopida is a species-rich taxon within the obligate anaerobic ciliate class Armophorea. Metopids have garnered increasing interest due to their potential to shed light on mitochondrial evolution and symbiotic relationship between eukaryotes and prokaryotes. However, the majority of metopid species remain poorly or incompletely studied, largely due to limitations in earlier research methodologies. In this study, three species, Bothrostoma aporobustum nov. spec., Brachonella mitriformis and Planometopus contractus, were examined using a morpho-molecular approach. The new species is distinguished by a short proboscis-shaped snout, an average of 33 somatic kineties, and 21 adoral membranelles. Brachonella mitriformis is characterized by a broad obpyriform body with a narrow and flattened posterior end, an average of 53 somatic kineties and 77 adoral membranelles, and unevenly distributed dikinetids on the preoral dome. Phylogenetic analyses confirmed the validity and monophyly of the genera Bothrostoma and Brachonella, and robustly resolved the phylogenetic position of Brachonella mitriformis. Representatives of geographically distant populations of Planometopus contractus are morphologically highly similar and cluster together with strong support in SSU rRNA gene phylogenies.