**5. Conclusions**

The newly described species is the second species of *Micractinium*, which lives in endosymbiosis with ciliates. If this species is exclusively distributed in a symbiotic association like *M. conductrix*, it cannot be decided so far. No GenBank record has been reported nor could be found in BLAST searching. *Tetrahymena utriculariae* is also the only mixotrophic species of this genus. Both organisms were only found once so far, which is probably caused by the lack of investigations. Fortunately, different aspects of this ciliate-green algal association can be studied in detail, because species are available in culture. Nothing is known about the specificity of this symbiosis. The easiness of cultivating makes this ciliate and its endosymbiont the perfect model organisms to study associations between ciliates and green algae.

**Author Contributions:** Conceptualization, T.P. and T.D.; methodology, G.P. and T.D.; software, T.P.; validation, T.P., G.P. and T.D.; formal analysis, T.P.; investigation, T.P., G.P. and T.D.; resources, T.P.; data curation, T.P.; writing—original draft preparation, T.P., G.P. and T.D.; writing—review and editing, T.P., G.P. and T.D..; visualization, T.P. and T.D.; supervision, T.P.; project administration, T.P.; funding acquisition, T.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Austrian Science Fund (FWF): gran<sup>t</sup> number P28333-B25.

**Conflicts of Interest:** The authors declare no conflict of interest.
