Phylum: Charophyta   Family: Desmidiaceae

Xanthidium armatum  L.A. de Brébisson ex J. Ralfs 1848

First described by Brébisson in Ralfs (1848: 112, pl. 18: a-g) and illustrated by Jenner.
Overall cell dimensions: L: 125-155 µm; B: 84-102 µm; Is: 34-38 µm.
One of the larger desmids frequently encountered in Sphagnum bogs and moorland peaty pools.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Ralfs, J. (1848). The British Desmidieae.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.