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Recently, I observed the pink ciliate Stentor igneus. It is interesting that the different stentor species have different coloration, especially the famous blue Stentor coeruleus. The photo below shows the fully extended Stentor igneus at low power (160x). The metachronal waves of the membranelles around the mouth of the ciliate can be clearly seen. The stripes of granules which give the ciliate its pink color are visible in the second, higher-power photo. These pigmented granules appear to serve two principle functions: one, as a deterrent to predation, and two, to orient the cell with respect to light, either toward or away from it. Interestingly, there was a paper published in 2014 in the Journal of Natural Products (https://pubs.acs.org/doi/pdf/10.1021/np5001363) in which the major component of pigment in the granules was isolated and given the name amethystin. Added after initial posting: After Bruce Taylor's clarification of the correct species shown in this post, I should add that whether amethystin is the same pigment in the granules of S. igneus as in S. amethstinus is not known.

Very nice pictures!

Stentor amethystinus has very dark cytoplasm, densely packed with endosymbiotic algae, and rows of purplish pigment granules. It is almost always found swimming freely, a very broad, pear-shaped (or sometimes amost spherical) cell, like the one in this video: https://www.youtube.com/watch?v=K-MH3VxidFs , and the one in this image by Wim van Egmond: https://www.sciencephoto.com/media/8799 ... micrograph

What you have here is almost certainly Stentor igneus, a slenderly trumpet-shaped species with pink or red cortical granules and no algal endosymbionts (zoochlorellae). For a key to Stentor species, and some more images of Stentor amethystinus showing the characteristic appearance, see: https://www.researchgate.net/publicatio ... ican_lakes

See also the redescriptions of both S. amethystinus and S. igneus in vol. 2 of the "ciliate atlas" by Foissner et al., pp. 340 -350: http://www.wfoissner.at/data_prot/Foiss ... _1-502.pdf

Hi Bruce, thanks very much for your comments and correction on this particular species of Stentor and the references you included. Always happy to be pointed in the right direction and get your comments!

Thanks tlansign and Bruce! Great references provided.