Abstract
The present paper documents the morphology and systematic positions of three new oligotrich ciliates, Parallelostrombidium obesum sp. nov., Parallelostrombidium ellipticum sp. nov., and Strombidium tropicum sp. nov., which were sampled from habitats with different salinities in southern China. Parallelostrombidium obesum sp. nov. is characterized by a fat body and the posterior portions of the girdle and ventral kineties extending transversely on the dorsal side. Parallelostrombidium ellipticum sp. nov. is recognizable by the anterior ends of the girdle and ventral kineties being close to each other and the posterior ends of the girdle and ventral kineties intersecting on the dorsal side. Strombidium tropicum sp. nov. is distinguished by a ventrally opened girdle kinety that is slightly spiralled with the right end shifted posteriad. Small subunit rRNA gene trees show that P.obesum sp. nov. and P.ellipticum sp. nov. fall into a mixed group composed of Parallelostrombidium and some Novistrombidium species, and that S.tropicum sp. nov. branches at the base of the clade containing non-Strombidium species. The relationships of Parallelostrombidium species and that of Strombidium species are both not resolved considering their low support values in our phylogenetic analysis.(c) 2015 The Linnean Society of London