The species composition and morphology of heterotrophic flagellates collected from bog hollows, bog pools, bog streams and watercourses were studied in the Pinega District, Arkhangelsk Oblast', NW Russia. 50 species of flagellates belonging to 4 macrotaxonomic clusters were recorded. Most of the flagellates were bacterivorous, 2 species were predators and further 2 species were omnivorous. The mire type in general and mire waterbodies in particular supported their own set of species (ANOVA: F = 15.5, p < 0.001). Thus, 34 species of heterotrophic flagellates were revealed in eutrophic mires (space between hummocks and streams), 26 in oligotrophic mires (hollows, bog streams, bog pools). The protist fauna was extremely poor in bog pools (2 species). Non-parametric MDS-analysis revealed 4 groups of communities: 1) hollows and laggs; 2) space between hummocks, hollow and stream; 3) degrading hollows-rimpi; 4) small lake. The species richness depended on electric conductivity (t = 0.65, p = 0.002). Descriptions, drawings and pictures of the most poorlyknown species are presented, taking into account particular structures of the cell. All species discovered are new to the fauna of Arkhangelsk Oblast'.