Phylum: Charophyta   Family: Desmidiaceae

Cosmarium pyramidatum J. Ralfs 1848

These large pyramidal cells have been much confused and form part of a species complex. Kouwets (2025) has now broken them down into several species. The species under discussion is the largest of the group and can support 2-6 pyrenoids.
Cell dimensions (4): L: 77.4-82.2 µm; B: 49.1-52.8 µm; Is: 15.6-21.2 µm; Th: c.35 µm; L/B: 1.48-1.61.
Because of the earlier species-complex confusion, this taxon would seem to be much scarcer than at once thought. It prefers acidic, meso-oligotrophic, moorland pools and bogs.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.