Phylum: Charophyta   Family: Desmidiaceae

Cosmarium sp. Haclait 

This cell is quite close to Cosmarium subadoxum. Grönblad’s original figure (1934: 268, figs 5: B) shows only slight curvature of the sides and a broad, truncate apex. Finds from the Netherlands and France show more rounded and convergent sides giving a narrower apex. Cells in the light microscope occasionally show what appears to be intramarginal granules but SEM imaging revealed them to be mucus pores. The size of the central granule is variable. The cell depicted below fits the foregoing parameters; the only doubt is the upper sides, which are straight. However, it was found in an acidic moorland bog, which differs markedly from C. subadoxum’s known habitat of circumneutral waters.
Cell dimensions: L: 11.1 µm; B: 10.4 µm; Is: 3 µm; Th: 6.3 µm; L/B: 1.07.

References: 
Grönblad, R. (1934). A short report of the freshwater-algae recorded from the neighbourhood of the Zoological Station at Tvärminne.
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.