So far I could find only one specimen of Metopus extentus in February 2022 in the Purren pond. This fits the description of Kahl, who describes the species as “rare” which can be found in winter and spring.

Metopus extentus is easily recognized by its stately size of about 160 µm (my specimen was 143 µm long) and the adoral zone extending obliquely across the ventral side (s. figs. 1 a and 1b). The mouth opening is below the middle of the cell, at the border of the posterior third. I could not observe the brown granules in the ectoplasm described by Kahl, although the specimen appeared brownish at lower magnification (s. figs. 1 a-c). However, this was due to the contents of the food vacuoles. Unfortunately, my specimen was completely filled with food vacuoles containing mainly rhodobacteria in various stages of digestion. Thus, I could only clearly recognize the rod-shaped macronucleus (s. fig. 3b), which, according to Kahl, should sometimes be completely curled up or just one end. I could not clearly identify the micronucleus, since it could also be the optical section through a rolled-up end of the macronucleus (s. fig. 3 b).

In the literature and on the internet I often found the name “Metopus extensus”. However, Kahl has called this species Metopus extentus. I suspect a transcription error behind it.