So far, I have only been able to find a single specimen of Cyclidium pellucidum. The specimen was found in a sample with decaying aquatic plants from the Simmelried. However, I only discovered it after placing the coverslip, when the specimen was already slightly squashed.

There is only a very brief description and a drawing of Cyclidium pellucidum by Kahl (1935). The species, at about 40 µm in length, is already one of the larger species within the genus Cyclidium. The essential characteristic, however, are the extrusomes arranged scattered beneath the pellicle (s. fig. 1 b). Kahl does not specify the length of the extrusomes. According to my measurements, the thin, rod-shaped extrusomes are consistently 4.6 µm long. Because of the presence of the extrusomes, Cyclidium pellucidum cannot be confused with any other species. Kahl suspects it might be a form of Calyptotricha lanuginosa (syn. Cyclidium lanuginosum). However, Calyptotricha lanuginosa lives in a lorica, has two elongated apical cilia, and the extrusomes of this species are very short and inconspicuous.

In the macronucleus of my specimen of Cyclidium pellucidum, I was able to recognize several, plate-shaped nucleoli arranged marginally (s. fig. 1 f). Kahl roughly indicates these in his drawing but does not mention them in his description. It remains unclear whether this is a consistent characteristic.