Description and Molecular Phylogeny of a Novel Hypotrich Ciliate from the Soil of Marche Region,Italy; Including Notes on the MOSYSS Project

The morphology and morphogenesis during cell division of a new stylonychine hypotrich, Rigidocortex quadrinucleatus n. sp., were investigated using live observation and protargol staining. The new species was isolated from soil samples collected from an organic farm in the Marche Region, Italy, in framework of the MOSYSS project. Rigidocortex quadrinucleatus is characterized as follows: cell size about 180 × 80 μm in vivo; four ellipsoidal macronuclear nodules; 44 adoral membranelles: 18 fronto‐ventral‐transverse cirri consisting of three frontal, four frontoventral, one buccal, three ventral, two pretransverse, and five transverse cirri; dorsal kinety 3 with multiple fragmentation; resting cyst with hyaline ridges. Rigidocortex quadrinucleatus mainly differs from the type species R. octonucleatus in having four (vs. eight) macronuclear nodules. Rigidocortex quadrinucleatus can be easily confused with Sterkiella cavicola since both have a rather similar ventral ciliature; however, they can be separated by the slightly higher number of cirri in the left marginal row that runs along the posterior cell's margin in R. quadrinucleatus. Morphogenesis on the ventral surface is highly similar to that of Sterkiella species, but differs significantly on the dorsal surface (multiple vs. simple fragmentation of dorsal kinety 3). Phylogenetic analyses based on SSU rRNA gene sequences consistently place the new species within the stylonychine oxytrichids, clustering closer to Gastrostyla steinii than to S. cavicola.