So far I have only found Dysteria monostyla once in a fire-fighting pond on the island of Hiddensse. The fire-fighting pond is located near the Hiddensee Biological Station in a south-easterly direction. It contains fresh water.

The samples from the fire-fighting pond contained only a few specimens. Dysteria monostyla has actually been described as a marine species, but the species appears to be adaptable.

The characteristics of my Dysteria monostyla population are consistent with Kahl’s description apart from the length of the specimens. Kahl give a range from 80–100 µm while the specimens of my population had a length of about 50 µm. However, it is possible that the variability in size is also greater than previously known, as Wang et al. (2019) described a population of Dysteria monostyla from the China Sea with a length of 40–70 µm.

The almost rectangular body shape of Dysteria monostyla is very characteristic. At the posterior end there is a spine on the right side, which probably has a sensory function. This is located at the end of a groove formed by the dorsal and ventral plate. The strongly reduced ciliatur in the form of a narrow band is localized in this groove. The cytophyryngeal basket is clearly arranged diagonally and the distal end of the nematodesmal rods are connected with a complex structure that is difficult to interpret under the light microscope. The macronucleus consists of two parts, similar to the related genus Trochilia. There are two contractile vacuoles on the right side.