Phylum: Charophyta   Family: Desmidiaceae

Staurastrum ophiura P. Lundell 1871

First described and illustrated by Lundell (1871: 69, pl. 4: 7). Similar to Staurastrum verticillatum but that species is larger with more pronounced granules at the base of the semicells. They occupy the same habitat type.
Overall cell dimensions: L: 65-91 µm; B: 130-170 µm; Is: 20-26 µm.
An Atlantic distribution from Scandinavia to Ireland and across to north America. Prescott et al. (2001: 266) note: “Widely distributed throughout the United States and Canada …” and yet they only quote West, West & Carter’s (l.c.) cell dimensions. It is now a rare desmid in Scotland.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Lundell, P.M. (1871). De Desmidiaceis, quae in Suecia inventae sunt, observationes criticae.
Prescott, W.G. et al. (2001 reprint). A Synopsis of North American Desmids. Part II, Desmidiaceae: Placodermae, Section 4.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.