Morphology of three Litonotus species (Ciliophora: Pleurostomatida) from China seas, with brief notes on their SSU rDNA-based phylogeny.

The morphology and ciliary pattern of three brackish pleurostomatid ciliates, Litonotus gracilis spec. nov., L. tropicus spec. nov., and L. duplostriatus, were investigated. Litonotus gracilis differs from its congeners by body size (200-400×15-40μm in vivo), body shape (slenderly spindle-shaped, long neck), the number of somatic kineties (6-7 left and 11-17 right somatic kineties), long bar-shaped extrusomes arranged along oral slit, tiny cortical granules arranged like honeycomb, one subterminally located contractile vacuole and, usually, four macronuclear nodules. Litonotus tropicus is characterized by four contractile vacuoles dorsally located, 8-11 right and four or five left somatic kineties. Litonotus duplostriatus is lanceolate-shaped, with 11-14 right and five or six left somatic kineties, one subterminally located contractile vacuole, fusiform-shaped extrusomes distributed along oral slit. Litonotus dragescoiPan et al., 2013 is not a valid name, it still be named as Litonotus fasciolatus (basionym Loxophyllum fasciolatusDragesco, 1966). Molecular phylogenetic analyses based on SSU rDNA sequence data indicate that neither the family Litonotidae nor the genus Litonotus is monophyletic, and L. gracilis has a closer relationship with the genus Kentrophyllum than with other Litonotus species.