Shedding new light on stylonychid ciliates: A case study of Tetmemena and Pleurotricha (Ciliophora, Spirotrichea, Hypotrichia, Dorsomarginalia)

Abstract

We studied three ciliate species from freshwater habitats: Tetmemena indica Bharti et al., 2019 from Kenya and Tetmemena pustulata (Müller, 1786) Eigner, 1999 and Pleurotricha setifera Engelmann, 1862 from Austria. Tetmemena indica had a rigid body measuring 73 × 33 μm in vivo, a shortened dorsal kinety 4 (DK 4), and a cyst with a smooth surface. Tetmemena pustulata was similar to the original and other populations described near the type locality, characterized by a body size of 97 × 40 μm in vivo, having a bipolar DK 4, and a process-bearing cyst. Pleurotricha setifera measured 156 × 60 μm in vivo, with 24-26 frontal-ventral-transverse cirri, one left and one right marginal cirral row, an adoral zone of membranelles occupying 54% of the cell length on average, and undulating membranes arranged in an Oxytricha-like pattern. The gene phylogenetic analyses of the SSU rRNA sequences revealed that T. indica clustered within the T. saprai/T. indica complex and T. pustulata formed its own lineage within the Tetmemena subclade. Both species differed in SSU rRNA gene sequences, DK 4 length, and cyst morphology. Pleurotricha setifera was morphologically and molecularly similar to Gastrostyla setifera (Engelmann, 1862) Kent, 1882 and Pleurotricha oligocirrata Park et al., 2017. Consequently, we clarified the synonymy of P. setifera and proposed a neotype for T. pustulata.