Monographic treatment of Paraholosticha muscicola (Ciliophora, Keronopsidae), including morphological and molecular biological characterization of a brackish water population from Korea.

Paraholosticha muscicola, type species of Paraholosticha Wenzel, inhabits mainly terrestrial habitats, but also freshwater. A brackish water population from Korea is described, the first record from such a habitat. Principal component analysis shows that this population is more similar to a terrestrial population from Denmark than to a population from Antarctic soil. Keronopsids have two strong morphological/ontogenetic apomorphies (frontal corona formed from anlagen I-III; division in cysts). However, the SSU rRNA sequence of the Korean population does not cluster with that of the Antarctic population in the phylogenetic tree, but both branch off consecutively and immediately before a mixture of other non-dorsomarginalian hypotrichs, including two further keronopsids. Furthermore, the keronopsids cluster in the phylogenetic network, providing phylogenetic conflicts, which cannot be exemplified in the conventional gene tree. To complete the picture of P. muscicola, we provide a detailed overview about nomenclature, history, taxonomy, and its geographic distribution. From the four synonyms proposed so far, we tentatively accept only P. lichenicola and P. ovata. Paraholosticha algivora is likewise very similar. Thus we propose to include these three taxa as members of the P. muscicola complex. Stylonethes sterkii and P. algivora are transferred to Paraholosticha Wenzel. A key to the Paraholosticha species is provided.