Epistylis pygmaeum lives epizoically on large rotifers and crustaceans of the plankton. Epistylis pygmaeum is found particularly frequently on Keratella and Brachionus.

The examination of epizoic ciliates such as Epistylis pygmaeum is not easy because they contract or detach from the host with increasing coverslip pressure. Taking photos very quickly has proven to be the best method. To do this, I already make all the settings for the lens I want to photograph with later. After putting on the coverslip, I look for a suitable object at the lowest magnification (without changing the settings) and immediately go to the preset magnification. This does not always lead to success, but sometimes it does.

Epistylis pygmaeum can be recognized by its almost spherical body shape and that the specimens do not sit on long, branched stalks. Instead, the stalks are very short and if the specimens are close together, they can only be recognized when the layer thickness is reduced (s. fig. 3). The stalks of the genus Epistylis are not contractile and are usually dichotomously branched. In Epistylis pygmaeum they are particularly short. The macronucleus is horseshoe-shaped and lies transversely in the anterior half (s. fig. 4 a). There is only one contractile vacuole (s. fig. 3). Another important characteristic of Epistylis pygmaeum is the wide striation of the pellicle (s. fig. 4 b).