Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus connatus (P.M. Lundell) K. Thomasson 1960

A small cell with wide-open sinuses from an angular base. Semicells bowl-shaped with a truncate apex that is occasionally retuse. Spines from the apical angles pointing upwards. Cells are tri-radiate.
Cell dimensions: L: 22-24 µm; B: 21-24 µm.; Is: 6-8 µm; Sp: 7-9; Overall: L: 34-45 x B: 25-35.
An acidophile of moorland pools and bogs. Probably widespread in such habitats but not common.

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.