Morphology and molecular phylogeny of two soil species of Holostichides (Ciliophora, Hypotrichia) collected from eastern China, including a new species and a new subspecies

Newly discovered hypotrich ciliates with evolutionary innovations are challenging to the established systematics and greater interest. Based on living morphology, infraciliature, and SSU rDNA, two bakuellid taxa—including a new species and a new subspecies—collected from subtropical soil environments in eastern China were investigated in the present study. Holostichides (Extraholostichides) eastensis ningboensis n. subsp. is characterized as follows: size in vivo 150–230 × 45–60 μm; cortical granules green and spherical; 3–5 small cirri arranged longitudinally posteriorly to middle frontal cirrus; row of 19–24 frontoterminal cirri exceeding half of the body length; 4–6 caudal cirri. Holostichides (Extraholostichides) muscus n. sp. is defined as follows: size in vivo 140–175 × 40–65 μm; cortical granules green and spherical; one or two small cirri posteriorly to the middle frontal cirrus; row of 3–6 frontoterminal cirri right of the midventral complex; three or four caudal cirri. Phylogenetic analyses based on SSU rDNA sequences revealed the systematic positions of these two new taxa and supported their validity as distinct subspecies and species, respectively.