In Andean lakes a distinctive assemblage of large mixotrophic ciliates (>80 μm), dominated by the peritrich Ophrydium naumanni Pejler and the heterotrich Stentor araucanus Foissner & Wölfl, has been previously reported (Wölfl, 1995; Modenutti, 1997; Queimaliños et al., 1999; Modenutti et al., 2000). These two species have been found only in large, deep ultra-oligotrophic lakes (area >5 km2, Zma...