Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus pterosporus (P.M. Lundell) P. Bourrelly 1966

Very similar to Std. crassus but with more pronounced mamillate apical angles and longer spines. There are also some similarities with Std. omearae. These are easily split by the shape of the zygospore, but they are rarely encountered. Std pterosporus has rectangular spores with the gametangial semicells attached to the corners like wings, hence the specific epithet: pteron means wing. Most Staurodesmus species have globose zygospores with projections.
Cell dimensions: L: 11-18 µm; B: 11-21 µm; Is: 5.3-8.5 µm; Sp: 2-5 µm; Overall LxB: 13-18 x 15-26.
An acidophile of little-known distribution. Current finds have been from moorland pools and lochs but rarely found.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Van Westen, M. (2024). Sieralgen in Drenthe.