A large ciliate whose whole surface is densely covered with cilia is darting around. It pauses for an instant and then dashes into a group of particles. This violent activity disturbs the peaceful habitat occupied by small algae and flagellates.
Commentary by Prof. Yuji Tsukii, Hosei University This organism belongs to genus Frontonia. From its long, flat body, it may be Frontonia leucas.
In the first part of this video (0:06~), the organism is opening its mouth toward a glass surface, probably because it found some kind of food there. Later it gives up and swims away. In fact Frontonia swallows similar-sized diatoms, which can be seen in the following link.
A second ciliate with a slightly slender shape appears in the later part of this video. The shell of a diatom inside its cytoplasm indicates this ciliate may also be Frontonia, which has swallowed this diatom shell. In Japanese Frontonia is called “Kuchisake-mizukemushi”. This Japanese name suggests an organism that often swallows food that is longer than its body. This may be why the organism becomes elongated.
It is difficult to determine the exact species for two reasons. First, the front view of the organism is not clear in this video. Second, many types of Frontonia remain unclassified, so identification of this organism is rather difficult.
Small Halteria ciliates and numerous diatoms are swimming in the spaces among particles. From behind one particle, a Euglena flagellate shows half of its body. Halteria and a larger ciliate busily swim around Euglena’ hiding place.
Commentary by Prof. Yuji Tsukii, Hosei University The first organism to appear is Halteria.
Flagellates and ciliates gathering around a food source
Various sizes of flagellates and ciliates are swimming around, and they sometimes enter aggregates containing a variety of foods. One of the large ciliates is 400 microns in diameter, dark brown and oval shaped. The side-view of the organism shows it is slender, slightly narrow at both ends, and entirely covered with short cilia. Its motion has become slow because it is bloated with food from successful foraging.
Commentary by Prof. Yuji Tsukii, Hosei University The leading character in this video is Frontonia acuminata. In contrast with other ciliates in the Frontonia group whose cytostome is located in the center of the “abdomen”, the cytostome of Frontonia acuminate is slightly shifted from the actual center. In this way the organism resembles Disematostoma, but from other criteria, it can be identified as Frontonia. For example, the top of Disematostoma is slightly pointed, but the top of this organism is round like others in the Frontonia group.