I find Setopus tongiorgii rarely but regularly in the Simmelried. I have not yet been able to find this species in my other sampling sites. In the last 10 years the number of finds has increased significantly. I find Setopus tongiorgii mainly in the siltation zone, where aerobic and anaerobic zones are close together.

Setopus tonigiorgii can be recognized even at small magnifications by the different lengths of the caudal spines (s. fig. 6). The left spine is always shorter than the right. In the similar species Setopus bisetosus, both caudal spines are the same length. In addition, the spines of Setopus tonigiorgii all have a secondary spine, including the spines on the trunk, neck and head. This also distinguishes Setopus tonigirogii from Setopus chatticus, whose spines have two secondary spines.

In my population of Setopus tonigirogii, I found deviations from the description by Balsamo (1983). On the one hand, my specimens were about 20 % longer (without caudal spines) than indicated by Balsamo and on the other hand, the terminal scales of my specimens were all oval or elliptical with a keel and not triangular with a keel and short spine. However, as the species has only rarely been found and studied so far, these findings may also be within the range of natural variability.

More information and images on Setopus tonigiorgii: Michael Müller-The small world of freshwater gastrotrichs-Setopus tongiorgii