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: 31-43 µm; B: 34-46 µm; Is: 9-12 µm; L/B: 0.9.
Zygospore diameter: minus projections: c.29 µm; overall: c.51 µm
A common species found in circumneutral waters such as loch-margins, moorland pools and abandoned peat-cuttings.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Ralfs, J. (1848). The British Desmidieae.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.