Phylum: Charophyta   Family: Desmidiaceae

Xanthidium armatum  J. Ralfs 1848

A large cell with the sinus open from the start. Each semicell supports six stout spines, which are usually bi- or tri-furcate. The large corona in the centre of the semicell comprises a ring of eight simple or emarginate teeth.
Cell dimensions: L: 116-139 µm; B: 71-88 µm; Is: 34-37 µm; Sp: 9-16 µm; Th: c.80 µm; Overall LxB: 130-155 x 92-104 µm.
A common element in acidic waters such as loch-margins and moorland pools, often with Sphagnum.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M.C. (2024). Sieralgen in Drenthe.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.