Phylum: Charophyta   Family: Desmidiaceae

Cosmarium sphagnicola W. & G.S. West 1897

There are several similar small cells that display four granules in an asymmetric configuration. They are much confused, and more research is needed to better understand them. It may be possible to separate some of them on habitat preferences.
Cell dimensions: L: 9-11.5 µm; B: 10-13.5 µm; Is: 4.5-7.2 µm; Th: 5-7 µm; L/B: 0.86-0.99.
Fairly common in acidic habitats such as moorland pools and bogs, including with Sphagnum.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.
West, W. & West, G.S. (1897). A contribution to the freshwater algae of the south of England.