Abstract The internal transcribed spacer regions （ITS1 and ITS2） and 5.8S rRNA genes were sequenced in six populations of four Aspidisca species, namely A. leptaspis, A. orthopogon, A. rnagna and A. aculeata. Phylogenetic trees were constructed by means of Bayesian inference （BI）, Maximum Parsimony （MP）, Neighbor-Joining （NJ）, and Maximum Likelihood （ML） to assess the inter- and intra-species relationships within the genus Aspidisca. All trees show similar topologies with stable supports and indicate that： （1） four well known groups, i.e., Oligotrichia, Stichotrichia, Choreotrichia and Hypotrichia, are distinctly outlined within the class Spirotrichea, and all are monophyletic other than Hypotrichia; （2） members of Aspidisca can be distinguished well, based on the ITSI-5.SS-ITS2 region sequences, and A. leptaspis and A. magna shared a closer relationship than other species; （3） Aspidisca and Euplotes branch early in the subclass Hypotrichia. To compare the phylogenetic relationships based on different genes, SSU rRNA trees were also constructed with nearly the same species inclusion, which revealed different topologies of inter-species, inter-genera and inter-subclasses.
