If you follow microscopesandmonsters, you’ll have already seen this under the appropriate title “Little pond of horrors…“, but I thought I’d share since it shows an ecological interaction involving a volvocine alga, Eudorina:
Unfortunately, we know very little about the ecological interactions of volvocine algae, so if this happens in nature, it would be important to know. I do wonder about that, though. The Eudorina in the video seem to be immobilized; normally they would be swimming at a rate of several colony diameters per second. The amoebae in the video aren’t moving nearly fast enough to capture a colony moving at this rate: note that the video is sped up 125-250x.
More about Arachnomyxa amoebae is in this article by Michael Marshall.