I find Tropidoatractus acuminatus regularly in the Purren pond and the Simmelried. The occurrence of this ciliate seems to be quite different. For example, Foissner describe the occurrence as “very rare”, while Kahl describes it as “common, never frequent”.

Tropidoatractus acuminatus is clearly and easily identifiable by its 7–8 distinct ribs, which running clockwise over the body (s. figs. 1 a and 2 e). The posterior end is elongated to a pointed spine (s. fig. 2 d). The specimens are usually longer than 100 µm. However, Tropidoatractus acuminatus is known to be very rich in form. Thus, also strongly broadened, stocky forms can be found and those with a very long terminal spine. In addition, dwarf forms of Tropidoatractus acuminatus can be found (see below).

The anterior end is flattened and curved ventrally. On the anterior margin of the apikal dome runs the perizonal stripe, with densely standing, long cilia (s. fig. 2 c). The somatic cilia are arranged in pairs between the ribs (s. fig. 5). In my population the macronucleus was usually quite long and ellipsoidal (s. fig. 4). It was mostly found in the anterior third of the body with an attached, spherical micronucleus (s. fig. 4). I could not detect any symbiotic bacteria in the cytoplasm and none have been described so far. The adoral zone is located on the right side at the anterior end. It is partially covered by the ribs. From the right side, however, it can be seen well (s. fig. 2 a and 2 b).