Redescription and phylogenetic position of the terrestrial ciliates Gastrostylides dorsicirratus and Heterourosomoida lanceolata (Hypotricha, Dorsomarginalia).

The morphology and infraciliature of two soil hypotrichous ciliates, Heterourosomoida lanceolata (Shibuya, 1930) Singh and Kamra, 2015 and Gastrostylides dorsicirratus (Foissner, 1982) Foissner, 2016, were investigated using live observation and protargol staining. The Chinese population of H. lanceolata differs slightly from other populations in the body size in vivo, the relative length of the adoral zone, the number of right and left marginal cirri, the total number of dorsal bristles, and the number of micronuclei. The Chinese population of G. dorsicirratus corresponds well with Austrian and Indian populations. We also document the morphogenetic processes during binary fission of G. dorsicirratus, including the formation of the frontoventral-transverse cirral anlagen in a primary pattern. In addition, phylogenetic analyses based on SSU rDNA sequence data reveal that the two populations of G. dorsicirratus for which data are available cluster together with full support and form a clade with Heterourosomoida sinica and two populations of H. lanceolata.