Reconsideration of the phylogenetic positions of three stichotrichous genera Holosticha, Anteholosticha and Pseudokeronopsis (Spirotrichea: Ciliophora) inferred from complete SSU rRNA gene sequences

The small subunit rRNA (SSU rRNA) gene for six marine stichotrichs, Pseudokeronopsis carnea, P. flava, Holosticha heterofoissneri, H. diademata, H. bradburyae and Anteholosticha manca, was sequenced and characterized. Using this molecular information, the phylogenetic positions of three related genera, Pseudokeronopsis, Holosticha and Anteholosticha were determined. The results indicate that the family Urostylidae is clearly separated from the family Pseudokeronopsidae. The present phylogenetic analyses unambiguously placed Pseudokeronopsis close to Holosticha, and support the conclusion that these genera should be regarded as the members of the order Urostylidae within the stichotrich clade. Furthermore, the results of this study also support the monophyly of the genus Pseudokeronopsis, the redefinition of Holosticha s. str. and the placement of Anteholosticha in a clade separate from Holosticha.