Phylogenetic position of three Condylostoma species (Protozoa, Ciliophora, Heterotrichea) inferred from the small subunit rRNA gene sequence

The systematically poorly known ciliate genus Condylostoma was erected by Vincent in 1826. About 10 morphotypes have been reported, but any molecular investigations concerning this group so far are lacking. In this work, the small subunit ribosomal RNA (SS rRNA) gene of three marine Condylostoma species was sequenced, by which the phylogenetic trees were constructed by distance-matrix, maximum parsimony and Bayesian inference methods. The results show that (1) all the trees have similar topologies with high supports; (2) Condylostoma is mostly related to the genus Condylostentor; and (3) three Condylostoma species as well as Condylostentor auriculatus cluster together and form a sister group with other heterotrichs. This is moderately consistent with the assessment of phylogenetic relationships of Condylostoma-related heterotrichs from the morphological information. The phylogenetic relationship of some other related heterotrichs, Peritromus, Folliculina, Stentor and Blepharisma, has been also discussed.