Actinobolina radians — A ciliate that resembles a heliozoan

Actinobolina is an unusual, predatory ciliate. The feeding form of the cell has stiff, extensible tentacles which are used to stun and capture large prey, such as rotifers, flagellates and other ciliates. When feeding, it could easily be mistaken for a heliozoan, except for the lush coat of cilia that surround the cell body, under the tentacles. When moving to a new spot, it retracts its tentacles , and looks like any other ciliate. We see this transformation at the end of the video. Several species of Actinobolina have been described. I’ve identified this one as A. radians because of its size, but was unable to see any other distinctive features, such as the macronucleus. This specimen has a distinct “waist” at the equator of the cell, so it is probably in the early stages of division.

Size: 90 μm long, 75 μm wide 40X, 100X oil immersion Olympus BHB w/ MU300 camera