I have only found Disematostoma buetschlii three times so far. Although it is a planktonic species, I found isolated specimens in June 2015 and June 2018 in the Simmelried between floating plant masses. In August 2024, I then found a mass development in the plankton of the Mühlhalden pond. Lauterborn and Kahl found their specimens between April and November, which led them to suspect a winter form. I cannot confirm this observation.

The shape of free-swimming specimens is ventrally similar to that of Frontonia atra, with a tapered posterior end. The swimming speed of Disematostoma buetschlii is very fast, which means that details can only be examined in fixed specimens. The mouth opening in the anterior third is channel-shaped. On the left side there are adoral membranelles and on the right side several rows of cilia, which form the undulating membrane (s. fig. 4).

The macronucleus was always C-shaped in my population (s. fig. 7). It deforms and denatures quickly under coverslip pressure. The round micronuclei, which are adjacent to the macronucleus, are difficult to find because they also denature quickly. According to Martin-Gonzalez, Serrano, and Fernandez-Galiano (1990) there should be 3–4 micronuclei. In my specimens, however, I could only find two micronucle (s. fig. 8) or one micronucleus (s. fig. 9). Due to the instability described, however, I may have overlooked micronuclei.

Above the mouth opening runs a ladder-shaped preoral suture, which runs to the apical pole (s. figs. 3 b and 5). In squashed specimens it can be easily recognized. Below the mouth opening, near the posterior end, a postoral suture arises, which runs to the posterior end and reaches up to the middle of the dorsal side (s. fig. 6). At the end of the postoral suture the excretorion porus of the contractile vacuole is visible to the left (s. fig. 6).

In most of the specimens I found symbiotic algae, which accumulated especially in the apical end. At high magnification it can be seen that these are xanthophytes. The cells are spherical with a diameter of 8–9 µm. The cell wall is finely punctured. The protoplasm contains brick-red oil droplets, which are typical for xanthophytes. I could not find any information about the symbiotic algae in Disematostoma buetschlii in the literature. Possibly these algae are member of the genus Chlorobotrys. Kahl (1931) observed that the symbiotic algae disappear in winter and the specimens are then colorless. However, the number of symbiotic algae also seems to fluctuate greatly in the summer months. I was able to find some with very few algae cells among many green specimens.

It is easy to confuse Disematostoma buetschlii with the similar species Stokesia vernalis. However, Stokesia vernalis has a hump-shaped dorsal side and therefore appears cap-shaped when swimming. In addition, the macronucleus is elliptical and not curved. Stokesia vernalis also has 3–5 excretory pores of the contractile vacuole and not one, as in Disematostoma buetschlii.