The genus Oxytricha Bory de Saint-Vincent in Lamouroux, Bory de Saint-Vincent and Deslongchamps, 1824 comprises about 38 species distributed worldwide and has been considered to be a nonmonophyletic group. Based on living observations, protargol preparations, and a small subunit ribosomal RNA (SSU rRNA) gene sequence, we describe a new subspecies Oxytricha granulifera chiapasensis n. subsp. This new taxon is morphologically characterized by undulating membranes basically in a Stylonychia-pattern, six dorsal kineties, size in vivo ca. 60-120 × 20-40 μm, 21-30 right and 21-31 left marginal cirri, 22-29 adoral membranelles, and spherical cortical granules arranged in longitudinal rows on the dorsal side. In terms of the SSU rRNA gene sequence, the new subspecies differs from populations of O. granulifera from GENBANK by 7-35 nucleotides. Phylogenetic analyses showed that Oxytricha granulifera gene sequences were nested into three groups, with the new subspecies included in one of them. Oxytricha granulifera chiapasensis n. subsp. is different from Oxytricha granulifera granulifera Foissner and Adam, 1983 and Oxytricha granulifera quadricirrata Blatterer and Foissner, 1988 based on: (i) undulating membranes in Stylonychia-pattern, (ii) formation of a sixth dorsal kinety during morphogenesis, (iii) the adoral membranelles number, and (iv) inhabiting freshwater habitats.

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Ciliates are a morphologically diverse group of protists inhabiting aquatic and terrestrial ecosystems. We studied the taxonomy and ecology of free-living ciliates from a freshwater marsh in Central Mexico during the period from 2012 to 2013 during both dry and rainy seasons. We found 30 ciliate species recorded for the first time from Atarasquillo marsh in Mexico, most of which are common species in freshwater ecosystems. The species richness was higher during the dry season than rainy season. Five trophic groups were observed: bacterivorous, bacteria-algae-heterotrophic flagellate consumers (BAF-consumers), omnivorous, predators, and mixotrophic species. The trophic group composition changed according to the season and the environmental conditions, e.g. vegetation and water level. Generally bacterivorous ciliates were more frequent during the rainy season, meanwhile the omnivorous during the dry season; thus, the feeding strategies in ciliates were different between both seasons. Due to the fact that Atarasquillo marsh is in a deterioration process, ciliate records could be used to assess water quality.

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