Morphology and Phylogeny of Two Novel Ciliates, Arcanisutura chongmingensis n. gen., n. sp. and Naxella paralucida n. sp. from Shanghai, China.

The morphologies of two novel ciliates, Arcanisutura chongmingensis n. gen., n. sp. and Naxella paralucida n. sp., collected from Shanghai, China, have been investigated using live observation and silver staining methods. Arcanisutura n. gen. can be easily distinguished from related genera by its inconspicuous, oblique anterior suture. Arcanisutura chongmingensis n. sp. is mainly recognized by its elongated body with a tail-like posterior end, 25-33 somatic kineties, and 4-11 excretory pores. Naxella paralucida n. sp. can be distinguished from its congeners based on its two short nassulid organelles, fusiform trichocysts, 37-49 somatic kineties, and 16 nematodesmal rods. The small-subunit (SSU) rRNA gene sequences of these two species are presented, revealing the phylogenetic positions of Arcanisutura and Naxella. Phylogenetic analyses show that Arcanisutura forms a sister clade to other synhymeniid genera, namely, Chilodontopsis, Orthodonella, and Zosterodasys; Naxella is most closely related to Nassula spp. and is located within the monophyletic clade of the family Nassulidae.