Metopus nasutus is one of the most common metopid ciliates in the Simmelried and the Purren pond. Especially in the Purren pond this remarkably shaped Metopus species can be found reliably. Metopus nasutus is easily recognized by a trunk-shaped organelle located at the anterior end. This organelle of unknown function makes the species unmistakable.

In my population I could find specimens with body lengths between 90–170 µm, which extends the range given by Kahl (100–150 µm). The trunk-shaped organelle is passively dragged along when swimming and lies against the left side of the body, as Kahl describes it (s. fig. 7 a-b). Only once could I observe the organelle to be stretched forward (s. fig. 3 a-d). In this specimen the trunk-shaped organelle was also unusually long with 74 µm. Kahl gives a length of 10–30 µm. On which factors the length of the organelle depends is unknown. In any case, it can melt under mechanical stress (coverslip pressure).

At high magnification, many vesicles and granules can be seen in the trunk-shaped organelle (s. fig. 6). In one case, I was able to find an attached bacterium at the tip of the organelle (s. fig. 6). Possibly this is a coincidental constellation, however it made me think of the possibility that the trunk-shaped organelle may be used like a glue rod to collect bacteria and other food particles. This theory is supported by the observation that in some free-swimming specimens I had the impression that the trunk was sometimes located between the perizonal cilia and the adoral membranelles in the direction of the mouth opening (s. figs. 8 a-b and fig. 9). Possibly bacteria or other food particles are “brushed off” between the perizonal cilia and the adoral membranelles during this behavior.

Beneath the pellicle of Metopus nasutus a fringe of extrusomes about 1 µm long is located (s. fig. 5a), not mentioned by Kahl. Many symbiotic bacteria are visible in the cytoplasm (s. fig. 5 a), especially in the area around the macronucleus. In the food vacuoles I found colorless bacteria, green-yellow sulfur bacteria, pink rhodobacteria and small green algae.