Findings on three endocommensal scuticociliates (Protista, Ciliophora) from freshwater mollusks, including their morphology and molecular phylogeny with descriptions of two new species

Species of the ciliate genera Myxophyllum and Conchophthirus are found as endocommensals of terrestrial and freshwater mollusks, respectively. So far, there have been few studies of these genera and morphological data for most members are often incomplete. In the present work, two new species, Myxophyllum weishanense sp. nov. and Conchophthirus paracurtus sp. nov., and a known species, Conchophthirus lamellidens, were isolated from hosts in Lake Weishan Wetland, China. Taxonomic studies indicate that M. weishanense sp. nov. can be recognized mainly by the combination of about 60 somatic kineties on both ventral and dorsal sides and the presence of caudal cilia. Conchophthirus paracurtus sp. nov. differs from congeners in its body shape and size, having a glabrous area on the posterior right side, and having fewer somatic kineties. In addition, differences in their ITS2 (Internally Transcribed Spacer 2) secondary structures support the discrimination of the two new species from their highly similar congeners. An improved diagnosis for the poorly known species, C. lamellidens is also provided. Phylogenetic analyses reveal that members of the genus Myxophyllum belong to a fully supported clade that is sister to a large, poorly supported clade consisting of Hemispeiridae, Ancistridae, and several lineages of the nonmonophyletic Cyclidiidae. The Myxophyllum clade also includes Protophyra ovicola JQ956552, a possible misidentification. Sequences of the two new Conchophthirus species cluster with other congeners in a fully supported clade that is unrelated to either the 'typical' thigmotrichs or to pleuronematids, thus conflicting with the traditional classification, and may represent an orphan scuticociliate lineage.