I have only found Euplotes eurystomus once, in an old sample with decomposing water lily leaves, together with a large population of Paramecium aurelia. According to Foissner et al. (1991), Euplotes eurystoma is a rather rare species within the genus. The authors themselves did not find any specimens.

Euplotes eurystomus is notable for a very large, triangular oral field, which on the left side is bordered by a very pronounced adoral zone running in a distinct S-shape (s. fig. 5). Additionally, I noticed that the specimens often swim freely and do not walk along glass surfaces as frequently. The 5 transverse cirri are long and extend clearly beyond the posterior end (fig. 3 a-b). Furthermore, there are 2 caudal cirri at the posterior end and two marginal cirri on the left side (s. fig. 2 d). On the ventral side, a total of 9 cirri can be seen, divided into 6 frontal cirri, 1 buccal cirrus, and 2 frontoventral cirri (s. fig. 3 a). The latter are quite far apart from each other.

In the cytoplasm, I could identify the symbiotic bacteria mentioned by Foissner et al. (s. fig. 9). According to my observations, they are 8–10 µm long and about 1 µm thick. In the food vacuoles, I very frequently found phagocytized amoebae of the genus Nuclearia. Additionally, in the cytoplasm of all specimens of the population, round, strongly birefringent bodies of unknown composition were found. Some were vaguely dumbbell-shaped (s. fig. 7).