Phylum: Charophyta   Family: Desmidiaceae

Staurastrum anatinum var. longibrachiatum W. & G.S. West 1905

It differs from the nominate variety in having longer processes, tipped with three large spines. These are parallel to a little divergent. In apical view there is a series of intramarginal bifurcate dentitions.
Overall cell dimensions: L: 47-73 µm; B: 97-112 µm; Is: 11-15.9 µm; L/B: 0.49-0.68.
Currently only found in Scotland but could have a wider Atlantic distribution. It occurs in the plankton and marginal vegetation of acidic larger lochs where it is not uncommon.

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