Morphological, Ontogenetic and Molecular Data Support Strongylidiids as Being Closely Related to Dorsomarginalia (Protozoa, Ciliophora) and Reactivation of the Family Strongylidiidae Fauré-Fremiet, 1961

Document Type


Publication Date





Hypotrich ciliates, a large group of mainly free-living protists with highly diverse cortical structures, are commonly found in a broad variety of habitats worldwide. Methodological difficulties and insufficient faunistic studies have limited our understanding of their true biodiversity and phylogeny. In this report, two new Strongylidium species from China are investigated using live observation, protargol staining and 18S rRNA gene sequencing, and the evolution of strongylidiid ciliates is investigated based on morphological, morphogenetic and molecular data. Recently, the genera Strongylidium Sterki, 1878 and Pseudouroleptus Hemberger, 1985 were assigned to the family Spirofilidae Gelei, 1929. Given that these genera differ morphologically and phylogenetically from the type genus of Spirofilidae, Hypotrichidium Ilowaisky, 1921, their familial classification should be reconsidered. Moreover, the highly characteristic formation pattern of the mixed left ventral cirral row and other morphological features shared by Strongylidium, Pseudouroleptus and Hemiamphisiella Foissner, 1988, together with their 18S rRNA gene sequences, suggest that the three genera form a group closely related to Dorsomarginalia Berger, 2006. The family Strongylidiidae Fauré-Fremiet, 1961 is reactivated for these three genera.