Morphology and molecular phylogeny of three Epistylis species found in freshwater habitats in China, including the description of E. foissneri n. sp. (Ciliophora, Peritrichia).

The peritrich genus Epistylis is speciose, however many species lack complete morphological description based on modern criteria and/or molecular data. In the present study, one new species, i.e., E. foissneri n. sp., and two morphologically similar species, i.e., E. hentscheli Kahl, 1935 and E. vaginula Stokes, 1884, collected from freshwater habitats in China, were studied. Epistylis foissneri n. sp. is characterized by its extremely slender zooids encased in a gelatinous sheath, symmetrically dichotomously branched stalk, trochal band located at mid-body, contractile vacuole located on dorsal wall of infundibulum, infundibular polykinety 3 (P3) composed of three equal-length rows that terminate above infundibular polykinety 1 (P1), 105-110 silverlines between the peristome and the trochal band, and about 110 silverlines between the trochal band and the scopula. Epistylis hentscheli is characterized by its asymmetric pyriform zooids (average length ca. 160 μm in vivo), dichotomously branched stalk with transverse striations on the surface of the upper portion, P3 three-rowed and terminating slightly above P1, 60-75 silverlines between the peristome and the trochal band, and 55-90 silverlines between the trochal band and the scopula. Epistylis vaginula is characterized by its elongated body shape (about 100 μm in length in vivo), dichotomously branched and smooth stalk, P3 three-rowed and terminating above P1, 80-100 silverlines between the peristome and the trochal band, and 45-80 silverlines between the trochal band and the scopula. The small subunit ribosomal DNA gene (SSU rDNA) of these three species was sequenced and supported the validity of each. Phylogenetic analyses based on SSU rDNA sequence data revealed that all three morphospecies group with other congeners within the major clade of Epistylis.