I rarely find Metopus setifer in the Simmelried. It is easily recognized by the long caudal cilia, which distinguishes it from the similar species Metopus barbatus. Furthermore the body of Metopus setifer is not dorso-ventrally flattened.

Kahl gives only a very short description and a drawing of Metopus setifer (s. drawing above). The specimens of my population showed a few deviations from his description. More than half of the specimens I examined were longer than 90 µm, but never reached 100 µm. I have not found any specimens smaller than 80 µm. The body shape of my specimens was also often oval and not tapered posteriorly (s. figs. 2 a-c and 3 a-c). The caudal cilia reached individually quite different lengths. In some specimens they measured about one third of the body length (s. fig. 1 a-c) while in others they were longer than the body (s. fig. 4 a-c). Very characteristic of Metopus setifer is the cilia-free terminal cell pole. The caudal cilia arise laterally around the posterior cell pole up to the posterior third, but not at the cell pole, which is thus naked (s. fig. 3 a). Kahl does not mention this feature in his description, but reproduces it in his drawing (s. drawing above).