Holophrya teres is a very common ciliate that occurs in almost all of my sampling sites. The species has a complex life cycle (theront-trophont-protomont-tomont-tomit). The images below show the theront phase, with little ingested food. In the trophont and protomont phases, the specimens are completely filled with food vacuoles, rounded and opaque.

Important characteristics for the identification are the number of longitudinal rows of cilia, the size and the absence of symbiotic algae. The cell surface is covered by 80–110 longitudinal rows of cilia, which are located in furrows. The total number can only be seen in anterior or posterior views. In lateral view, about 40–50 longitudinal rows can be recognized in squashed specimens (s. fig. 4). Another characteristic feature of Holophrya teres is the shape of the mouth opening (s. drawing 4, above). The trichites of the oral basket are not arranged in a circle, but in an oval (s. fig. 8) or sometimes almost rectangular.

The similar species Holophrya discolor is smaller (usually 80–120 µm) and has only 35–64 longitudinal rows, i.e. about half as many as Holophrya teres. If the cytoplasm contains symbiotic algae and the cells are smaller than 160 µm, then it is Holophrya ovum.

In my population, the specimens of Holophrya teres were consistently longer than 250 µm. The oral basket consisted of about 40 trichites in most specimens. All specimens had about 20–30 caudal cilia. I had the impression that these were arranged in a circle around the posterior cell pole (s. figs. 3 a and 3 b).