I find Colpoda steinii in almost all moss samples that I pour rainwater over in Petri dishes. After a few days, populations of varying sizes occur. However, Colpoda steinii can also be found in hay infusions, soil samples and even in plankton.

Colpoda steinii can easily be confused with other Colpoda species, such as Colpoda ecaudata or Colpoda aspera. Colpoda ecauda, however, has several nucleoli in the macronucleus and not just a central one. Colpoda aspera is smaller and has a pointed apikal end. Both species also have no caudal cilia, like Colpoda steinii.

The two caudal cilia of Colpoda steinii are hard to see at high magnifications because they are constantly moving and are rarely in focus. It is therefore advisable to examine specimens at first at lower magnifications. The characteristic “beard”, which originates in the middle of the ventral side, is also striking. These are the long cilia of the left oral cilia. This dense field of cilia (polykinetid) is difficult to recognize under the light microscope. However, it is possible to distinguish between the left and right cilia of the mouth opening when focusing through.