Morphology, cell-division, and phylogeny of Schmidingerothrix elongata spec. nov. (Ciliophora, Hypotricha), and brief guide to hypotrichs with Gonostomum-like oral apparatus.

The hypotrich Schmidingerothrix elongata spec. nov., discovered in saline (20‰) soil of the Longfeng Wetland, Daqing, northern China, was studied using live observation and protargol impregnation. It is characterized, inter alia, by colorless cortical granules arranged in short rows, three frontoventral cirral rows with the rightmost extending far posteriorly, and 4-8, usually six macronuclear nodules. Cell division proceeds as in congeners and confirms the lack of dorsal ciliature. In phylogenetic analyses based on SSU rDNA, S. elongata is sister of S. salinarum+Paracladotricha salina. A re-investigation of the type slides of P. salina, type of Paracladotricha, revealed a misobservation in the original description. Since P. salina lacks, like Schmidingerothrix spp., a dorsal ciliature, Paracladotricha becomes a junior, subjective synonym of Schmidingerothrix with S. salina comb. nov. as fourth species. A review of the phylogenetic analyses dealing with Schmidingerothrix shows that its position is variable. However, together with the gonostomatid oral apparatus it can be hypothesized that Schmidingerothrix is a member of the Gonostomatidae or a close relative. A list of genera (14) and species (58) which have - like Schmidingerothrix - a gonostomatid oral apparatus, as well as a key to these genera are provided.