Morphological Redescription and Molecular Identification of Trichodina reticulata Hirschmann & Partsch, 1955 (Ciliophora, Mobilida, Trichodinidae) with the Supplemental New Data of SSU rDNA and ITS-5.8S rDNA.

During a survey of trichodinids in Chongqing, China, two populations of Trichodina reticulata Hirschmann & Partsch, 1955 were isolated from gills of the freshwater fishes, Carassius auratus and Ctenopharyngodon idellus, and 11 molecular samples containing small subunit (SSU) rDNA and internal transcribed spacer (ITS)-5.8S rDNA were newly sequenced. Both populations fell within the range of morphometry and corresponded well with the diagnostic morphological features of Trichodina reticulata Hirschmann & Partsch, 1955. It should be noted that one population possessed obvious central granules in the adhesive disc, while the other one did not. The detailed morphological redescription for these two populations is given in this work. Although some intraspecific differences were found, both populations were confirmed as Trichodina reticulata based on the morphological study and molecular data, including the sequence analysis of the primary and secondary structures of SSU rDNA, genetic distances and phylogenetic tree. Our study supports the assertion that central granules in the adhesive disc might be an auxiliary feature rather than a heritable character for determining taxonomic affiliations among trichodinids.