Phylum: Charophyta   Family: Desmidiaceae

Staurastrum avicula  J. Ralfs 1848

West & West (1923: 40) note: “Its uniform granulation and the pair of minute spicules at each angle of the broadly ovate semicells distinguish it.” Later authors include cells with more pronounced spines, which need to be compared with S. subcruciatum. Coesel & Meesters (2023: 221) note: “… is a taxonomically complex species that needs a serious revision.” Zygospore globose with long straight projections with a broadened base and furcate apices.
Cell dimensions: L: 28.7-36 µm; B: 32-41.4 µm; Is: 10-13 µm; L/B: 0.8-1.0.
Zygospore diameter: minus projections: c.29 µm; overall: c.51 µm.
A common species found in circumneutral waters with a bias towards slightly alkaline. Favoured sites include loch-margins, especially machair lochs.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Van Westen, M.C. (2024). Sieralgen in Drenthe.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.