Phylum: Charophyta   Family: Desmidiaceae

Cosmarium carinthiacum J. Lütkemüller in R.L. Grönblad 1942

A small cell that needs to be compared with similar sized and ornamented taxa. However, the defining characteristic of this desmid is the tri-undulate apex, which is unique.
Cell dimensions: L: 6.5-10.6 µm, B: 7-12 µm, Is: 3.5-5.3 µm; Th: 4-6.8 µm, L/B: 0.85-1.00.
This rather small desmid is reported as widespread but not common, it is, however, easily overlooked. An acidophile most likely to be found in oligotrophic waters such as peaty moorland pools, often in association with Sphagnum.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.
Van Westen, M.C. (2024). Sieralgen in Drenthe.