Lurking behind some particles, this ciliate (which may be Pleuronema) is waiting for food. The transparent membrane extending from the side of the body captures small flagellates. Some of these flagellates are carried into the food vacuole, but others manage to get free.
Commentary by Prof. Yuji Tsukii, Hosei University This organism belongs to genus Pleuronema.
A thin oval ciliate 150 microns long stands still between particles as if it wants to conceal itself.
Long surface cilia that extend in all directions do not move at all. A membranous structure continuously trembles on one side of the body. When other organisms approach, it immediately darts behind another particles and stays hidden for a while.
Commentary by Prof. Yuji Tsukii, Hosei University This ciliate is most likely Pleuronema marinum, which is one of the larger species in the genus Pleuronema.
There is a similar ciliate called Histiobalantium, but the whole cell surface of Histiobalantium is covered by two kinds of cilia both long and short.
Because these cilia are not visible in this video, the organism can be identified as Pleuronema marinum. The shape of its body also indicates Pleuronema rather than Histiobalantium.
After being collected from a paddy field, the sample was put on 1% agar plate with a drop of distilled water and kept for a few days.
The whole body of this ciliate is covered with short, stiff cilia. Compared to the cilia covering the soft body of a Paramecium, these needle-like cilia are probably for defending itself rather than for locomotion .
Commentary by Prof. Yuji Tsukii, Hosei University This ciliate moves actively in the first half but stands still in the latter half of this video. When it is standing still, we can see that the cell surface is covered with cilia and that the cell length is about 100μm. From these features, the organism is probably Pleuronema marinum.
Pleuronema is characterized by a curtain-like structure called a velum that is composed of long cilia arranged in a line around the cytostome (mouth). This structure is difficult to find in this video, probably because the cell is in a narrow space surrounded by aggregates.
Alternatively, this organism might be a ciliate called Histiobalantium natans.
Histiobalantium natans is smaller than Pleuronema marinum but has a similar appearance. It does not have a velum structure but instead has two types of cilia of different lengths. The longer cilia are about twice as long as the shorter cilia, and they are mixed on the cell surface.
Since we cannot see this mixture of cilia with different lengths in this video, the organism cannot be identified.