Morphological and Molecular Phylogeny of Two New Ciliate Species, Colpoda heilongjiangensis n. sp. and Bryometopus shii n. sp. (Protozoa, Ciliophora, Colpodea), from Northeastern China

This study describes two new species of ciliates, Colpoda heilongjiangensis n. sp. and Bryometopus shii n. sp., discovered in northeastern China. Colpoda heilongjiangensis n. sp. was collected from a sewage outlet in Harbin, characterized by its large size, broadly to slenderly reniform body shape, and unique ciliary patterns. Bryometopus shii n. sp. was found in a puddle near a waste disposal station, featuring a droplet-shaped or oval and distinct oral apparatus. The morphology of both species was investigated through live observation, protargol staining, and silver carbonate and dry silver nitrate impregnation. DNA extraction and SSU-rRNA gene sequencing were performed to determine their evolutionary relationships. Phylogenetic analyses based on SSU-rRNA gene data revealed that Colpoda heilongjiangensis n. sp. clusters with C. minima, while Bryometopus shii n. sp. has a close relationship with B. atypicus. This study also discussed the non-monophyletic status of the genus Bryometopus and proposed a revision to the family Tillinidae based on morphological and molecular evidence. These findings highlight the remarkable diversity of Colpodea and contribute to the understanding of their evolutionary relationships.