Stentor pyriformis Johnson, 1893

These Stentors, which are relatively non-contractile and have symbiotic algae, are very abundant in Mer Bleue samples. They differ from Stentor amethystinus in having multiple macronuclear nodules (2 or more) and no purplish pigmentation, so I have always identified them as S. pyriformis. However, S. pyriformis is described (by Foissner in his revision of the genus) as having colorless cortical granules. Looking a bit more closely, recently, I noticed that this variety has darkly pigmented cortical granules. I overlooked them, earlier, because they happen to be green, like the zoochlorellae around them. The pigmentation makes the cells very dark (almost black, sometimes).