I found this very tiny specimen in sediments of a Sphagnum pool along the Bert Bospad, the Netherlands. It resembles R. coerulea Penard, 1904, but is on the small size, c. 5 µm where R. coerulea is 8-18 µm. This species has about 2-4 relatively large extrusomes along its axopdia. It contracts its axopodia quickly when disturbed.
Two different specimens
Dried cell with scales visible