So far I have only found Prorodon margaritifer in the Simmelried and Bussenried. However, the species is quite rare in these locations. I find one specimen every 2 years on average.

In a fresh sample, Prorodon margaritifer immediately stands out due to its size of about 300 µm and its rapid swimming movements. The ciliate often pushes back and forth. The mouth opening is slightly shifted ventrally and numerous contractile vacuoles are scattered over the body, which lie directly beneath the pellicular (s. fig. 1 c). The longitudinal rows of cilia are very dense. Even at medium magnification the nuclear apparatus can be recognized, which consists of two ellipsoidal macronuclei and an oval micronucleus between them (s. fig. 5). This is a clear distinguishing feature from Holophrya teres, which has a round macronucleus with an attached micronucleus.

The mouth opening of Prorodon margaritifer is long oval or almost rectangular (s. fig. 4 a-b). In my specimens the oral basket consisted of 82–86 rods. Kahl described the contractile vacuoles with 4 excretory pores each. In my population, however, there was always only one excretory pore in all contractile vacuoles (s. fig. 6). The extrusomes are small and inconspicuous. I was able to observe club-shaped ones with a length of about 3.5 µm (s. fig. 7). A second type of extrusomes seems to be present. These could be slightly curved rods of similar length. However, I was not able to recognize them exactly.