Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus bulnheimii (M. Raciborski) F.R. Round & A.J. Brook 1959

An unusual Staurodesmus in having the sinus closed for the most part. It’s 2-radiate with fairly thick walls. The spines from the apical angles are convergent and vary in length.
Single cell dimensions: L: 39.1 µm; B: 31.1 µm; Is: 10.2 µm; Sp: 5-8; L/B: 1.26; Overall LxB: 42 x 35.
Found in slightly acidic, mesotrophic, waters such as moorland pools and bogs. A very rare desmid with only one site in the Outer Hebrides as of 2025. Taken from squeezed Sphagnum and algal sludge.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.