Morphology and molecular phylogeny of three heterotrichid species (Ciliophora, Heterotrichea), including a new species of Anigsteinia

Heterotrichs are generally larger than ciliates of other groups with a seemingly cosmopolitan distribution, and recent studies have demonstrated that they exhibit great biodiversity. In the present work, we investigated the morphology and small subunit rRNA (SSU rRNA) gene sequences of three heterotrichous species, including that of a new one, Anigsteinia paraclarissima spec. nov. The new organism is morphologically very similar to A. clarissima, however, it can be distinguished from the latter by the larger dimensions and more somatic kineties (25-32 vs. 18-26), and its sequence similarity of SSU rRNA gene is 97.14% which indicate that it is a distinct species. Detailed morphological and molecular data for Blepharisma bimicronucleatum are supplied together for the first time in this study. In addition, the morphology of a poorly known species, Spirostomum yagiui is redescribed and an improved species diagnosis is provided. Finally, based on phylogenetic analyses of SSU rRNA gene sequences data, the Spirostomum group contains two main clades based on the type of the macronucleus. Spirostomum yagiui was newly sequenced here and clustered with the other S. yagiui populations and positioned within the Spirostomum assemblage. The Anigsteinia clade, including A. paraclarissima and A. clarissima, clustered within the family Spirostomidae.