Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus aristiferus  (J. Ralfs) K. Tomasson 1960

A smallish cell with almost rectangular, wide-open, sinuses. Semicells about triangular with the apical angles bloated supporting spines of varying length. It occurs in tri- and quadri-radiate forms.
Cell dimensions: L: 22-30 µm; B: 25-3 µm.; Is: 5.7-8.5 µm; Sp: 7-18; Overall: LxB: 30-51 x 36-62.
A rare species found in the plankton of acidic waters. It would seem to have an Atlantic distribution.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Teiling, E. (1967). The Desmid Genus Staurodesmus. A taxonomic study.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.