This ciliate was described by Stokes as Ctendoctema acanthocrypta. Kahl (1935) adopted this name. However, Foissner et al. (1994) described the species as Ctedoctema acanthocryptum, arguing that the genus name Ctedoctema has a neuter gender and therefore the species name must end in “um”. Until a final decision has been made, I agree with the argumentation of Foissner et al.

Ctedoctema acanthocryptum is one of the most common ciliates. It is particularly common in waters with decomposing plant masses. Very often Ctedoctema acanthocryptum is confused with Cyclidium glaucoma because the jumping type of movement is similar. However, Cyclidium glaucoma has a plumper body and the contractile vacuole is terminal, whereas in Ctedoctema acanthocryptum it is clearly subterminal (s. fig. 2 c).

At higher magnification one can recognize further differences to the genera Cyclidium and Cristigera. The cilia in the anterior two-thirds of the body are arranged in pairs and are only single in the posterior third (s. fig. 5 c). When at rest, the cilia appear stiff like bristles and are spread out from the body. The long peristome, which also takes up two-thirds of the body, is striking. On the left side of the peristome is a triangular-shaped, undulating membrane. It slopes downwards towards the mouth opening (s. figs. 3 a-d and 4 a-d). The margin of the body appears slightly wavy. Damaged specimens form a transparent blister of cytoplasm, which always develops in the posterior third below the mouth opening. This could also be an important distinguishing feature from the genera Cyclidium and Uronema, which do not form this blister.