Epistylis rotatorium (Kahl, 1935)

Most likely ID: n.a.


Synonym: n.a.


Sampling location: Mühlhalden pond


Phylogenetic tree: Epistylis rotatorium



  • body broadly pyriform
  • length about 35 µm
  • macronucleus horseshoe-shaped, transversely located in anterior half
  • one micronucleus
  • one contractile vacuole adjacent to mouth funnel
  • distinct bulge of peristome
  • colonies of 2–8 zooids
  • stalk short, hyaline, in larger colonies dichotomously branched
  • wide striation of the pellicle
  • epizoic lifestyle on large pelagical rotifers
Epistylis rotatorium

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


The examination of epizoic ciliates such as Epistylis rotatorium 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 rotatorium 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 rotatorium 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 rotatorium is the wide striation of the pellicle (s. fig. 4 b).


Fig. 1: Epistylis rotatorium. L = 28–37 µm. Five specimens attached to the amictic egg of Keratella quadrata. Obj. 40 X.


Fig. 2 a-b: Epistylis rotatorium. L = 28–37 µm. Two focal planes of the specimens. Obj. 60 X.


Fig. 3: Epistylis rotatorium. L = 28–37 µm. The same group of specimens after reduction of layer thickness. Note the short, hyaline stalk (ST). CV = contractile vacuole, Ma = macronucleus. Obj. 60 X.


Fig. 4 a-b: Epistylis rotatorium. Two focal planes of the slightly squashed specimen. Note the wide striation of the pellicle. Ma = macronucleus, Mi = micronucleus. Obj. 60 X.


Fig. 5: Epistylis rotatorium. Two strongly squashed specimens. Ma = macronucleus. Obj. 100 X.