As a follow-up part of our studies of the tropical ciliate fauna carried out in the last decade, we investigated the morphology and phylogeny of three choreotrich ciliates, viz, Parastrombidinopsis costalis sp. n., P. pelagica (Fauré-Fremiet, 1924) comb. n. and P. minima Tsai et al., 2008. The new species is characterized by its unique asymmetrical cell shape, 19–21 collar membranelles, one buccal membrane, and eight unevenly distributed somatic kineties.An improved diagnosis of P. pelagica(Fauré-Fremiet, 1924) comb. n.is given based on the original and current studies, the species is characterized by a large cell size, an elongate obconical cell shape, 31–36 collar membranelles and 13–15 somatic kineties. The species P. minimais redescribed based on a new population with some new features supplemented.SSU rRNA genes of both the new species and P. minima were sequenced and a phylogenetic review of related taxa obtained has been performed in order to reveal their systematic relationships. The monophyly of the genus Parastrombidinopsis is highly supported in our phylogenetic analyses.
