New geographical records and molecular investigation of the ciliate Spirostomum

Spirostomum is a genus of large ciliates, and its species are distributed worldwide. However, there has been limited research conducted on their geographical distribution and genomics. We obtained nine samples of ciliates from eight regions in Liaoning Province, China, and conducted a study on their geographical distribution and characteristics. Morphological and second-generation high-throughput sequencing methods were applied to identify the species, and a phylogenetic tree was established to gain a deeper understanding of the geographical distribution and evolutionary relationships of Spirostomum in Northeast China. The results identified Spirostomum yagiui and Spirostomum subtilis as a newly recorded species in Northeast China region. There are now five species of Spirostomum that have been recorded in China, and new details on the genomic characteristics of Spirostomum yagiui were provided. In addition, this study also identified the main branches of Spirostomum teres and Spirostomum minus in northern China, and provided a theoretical basis for the existence of hidden species. Spirostomum yagiui is the first species in the family Spirostomidae to have undergone mitochondrial genome sequencing.