Morphology and Molecular Phylogeny of Two Soil Ciliate Species (Protozoa, Ciliophora) from the Changbai Mountain Region, China, Including a New Species

Soil ciliates are an important component of the soil micro-food web, playing key roles in organic matter decomposition and nutrient cycling. However, research on the species diversity and taxonomy of this group in the temperate forest soils of China is still limited. This study investigates the morphology and ciliary pattern of two ciliate species discovered in the Changbai Mountain region of northeastern China: Bryometopus changbaishanensis sp. n. and Apocolpodidium etoschense Foissner et al., 2002, using live observation and silver carbonate impregnation. B. changbaishanensis sp. n. is characterized by the following morphological features: size in vivo approximately 40–48 × 20–29 μm, 11–14 somatic kineties; the paroral membrane consists of about 16–26 dikinetids; and there are 11–15 oral membranelles. This species differs from B. atypicus in its smaller body size in vivo, fewer somatic kineties, and fewer oral membranelles. Apocolpodidium etoschense Foissner et al., 2002, exhibits the following morphological features: in vivo size approximately 48–85 × 19–35 μm, 16–20 somatic kineties, and a gently curved paroral membrane composed of about 13–20 dikinetids; its hypostomial organelle consists of three to five files, each containing approximately three to five monokinetids. Additionally, DNA extraction and SSU rRNA gene sequencing were performed to elucidate their evolutionary relationships. Phylogenetic analyses based on SSU rRNA gene data indicated that Bryometopus changbaishanensis sp. n. clusters with B. atypicus. This study also provides a redescription and supplementary definition of A. etoschense, with the Changbai Mountain population forming a fully supported cluster with previously sequenced data.