The biodiversity of euplotid ciliates in high-latitude regions has long been underestimated due to a historical research focus on mid- to low-latitude areas. This study describes three new species collected from high latitudes, Euplotes aspergilliformis sp. nov., E. borealis sp. nov., and E. verebkovi sp. nov. Euplotes aspergilliformis sp. nov. is characterized by medium body size (60-85 × 40-60 μm). It possesses nine frontoventral cirri, two marginal cirri and two caudal cirri with forked distal ends. It also has eight dorsal kinetids (with 13-17 dikinetids in the mid-dorsal kinety) and a double-eurystomus type silverline system. Euplotes borealis sp. nov. is a medium-sized (45-55 × 25-35 μm) freshwater ciliate. It can be recognized by nine frontoventral cirri, one marginal and two caudal cirri. It has nine dorsal kineties with about nine basal bodies in the mid-dorsal kinety, and a double-eurystomus type silverline system. Euplotes verebkovi sp. nov. features an elongated oval body (40-54 × 22-31 μm). It has ten frontoventral, five transverse, one marginal, and two caudal cirri. It possesses seven dorsal kineties with eight or nine bristles in the mid-dorsal row, seven conspicuous dorsal ridges, and a double-eurystomus type dorsal silverline system. Phylogenetic analyses based on molecular data revealed the systematic positions of the three new taxa and confirmed the validity of the three organisms as distinct species.
Keywords: SSU rDNA; biodiversity; molecular; morphology.