Urotricha castalia is a heterotrophic ciliate feeding mainly on small algae that appear simultaneously in lake plankton. In video ‚Urotricha castalia 1‘, we see the contractile vacuole in the posterior end of the cell and several elongated caudal cilia. In the video ‚Urotricha castalia 2‘, we see a squeezed individual with many intracellular bacteria (symbionts? parasites?) moving rapidly inside the cell. The image below shows the characteristic types of extrusomes (cell organelles extruded immediately by the ciliate when a predator approaches or to catch prey): arrows denote the fusiform about 6 µm long extrusomes in the unciliated posterior cell portion and the about 3 µm long extrusomes in the ciliated part of the ciliate.
Interestingly, from time to time (at 0.5 and 5.5 min in the video), flame-like protuberances appear in which the bacteria seem to form up and rotate). We have never observed that phenomenom before! If you have any idea on what is going on here, please contact us!