Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus convergens (C.G. Ehrenberg ex J. Ralfs) S. Lillieroth 1950

First described Ehrenberg in Ralfs (1848: 118, pl. 20: 3) and illustrated by Jenner as Arthrodesmus convergens. It was later moved by Lillieroth (1950: 264) to its current position. The length of the spines varies considerably and the cell-shape alters accordingly.
Cell dimensions (minus spines): L: 39-46 µm; B: 43-49 µm; Is: 10.6-15.8 µm.
Common in shallow, slightly acid, mesotrophic water, also in the tychoplankton.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Lillieroth, S. (1950). Über Folgen kulturbedingter Wasserstandsenkungen für Makrophyten- und Planktongemeinschaften in seichten Seen des südschwedischen Oligotrophiegebietes. Eins Studie mit besonderer Berücksichtigung der angewandten Limnologie.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.