Taxonomy and Phylogeny of Two New Zosterodasys Species (Protista: Ciliophora: Phyllopharyngea) from the Yangtze Estuary, China

The genus Zosterodasys is a widely distributed group of typical algivorous ciliates. It remains poorly investigated and its phylogeny has not been well resolved yet. In the present work, two new Zosterodasys species, Z. paraminutus sp. nov. and Z. shanghaiensis sp. nov., isolated from an intertidal zone in Shanghai, China, were investigated based on both microscopic observation of live and protargol-stained specimens and SSU rDNA analyses. Both new species possess a unique S-shaped synhymenium that completely encircles the body. Zosterodasys paraminutus sp. nov. is characterized by a body size of about 87–130 × 28–50 μm, an elongated oval body shape, 39–59 somatic kineties, 12–15 nematodesmal rods, and numerous contractile vacuoles arranged along both sides of the cell. Zosterodasys shanghaiensis sp. nov. is characterized by a 114–174 × 50–85 μm body size, an obovate body shape, 74–122 somatic kineties, 12–17 nematodesmal rods, and several contractile vacuoles scattered throughout the body. Phylogenetic analysis questions the monophyly of Zosterodasys, since Zosterodasys sp.5 and Zosterodasys sp.6 diverged from its congeners, indicating these two sequences might be misidentified. In addition, we also provide an updated identification key for the genus Zosterodasys.