Redescription of Keronopsis helluo Penard, 1922 from Antarctica and Paraholosticha pannonica Gellért and Tamás, 1959 from Alaska (Ciliophora, Hypotricha).

The morphology of Keronopsis helluo Penard, 1922, type species of Keronopsis, and Paraholosticha pannonica Gellért and Tamás, 1959, two little-known members of the Keronopsidae Jankowski, 1979, was described using standard methods. In addition, we sequenced the SSU rRNA of both species. Keronopsis helluo was isolated from a mossy soil from Robert Island (Antarctica) while P. pannonica was found in terrestrial moss from Alaska. Our data correspond very well with the original descriptions. The frontal ciliature of K. helluo is identical with that of Paraholosticha spp., indicating that some Keronopsis species (K. tasmaniensis, K. dieckmanni) are misclassified in the keronopsids. The type species has distinctly more transverse cirri (8-13) than K. wetzeli (1-3), type species of Parakeronopsis, which is thus perhaps a valid genus or subgenus. The phylogenetic analyses confirm the position of the keronopsids outside the Dorsomarginalia. The species sequenced so far (K. helluo, Paraholosticha muscicola, P. pannonica) emerge from a soft polytomy, which also comprises Bistichella-like species and a large cluster composed of amphisiellids, trachelostylids, and gonostomatids, that is, the method failed to resolve the relationships within the keronopsids. The Keronopsidae and the two species studied are characterized based on previous studies and our data.