Phylum: Charophyta   Family: Desmidiaceae

Staurastrum bulbosum  (W. West) P.F.M. Coesel 1996

First described and illustrated by West (1892: 182, pl. 23: 11) as Staurastrum gracile subsp. bulbosum. It was later raised to species rank by Coesel (1996: 1020). The main distribution for this species is the Atlantic coastal regions. The main diagnostic features are two spines at the end of the processes and simple dentation at the apices. However, some two-spined cells have small, bifurcate dentition, which overlaps with the variety cyathiforme. The zygospore is rarely recorded: it has 10 projections visible in face view with bifurcate (occasionally trifurcate) apical appendages.
Cell dimensions: L: 50-70 µm; B: 70-100 µm; Is: 11-12 µm.
Zygospore: minus projections: 24-36 µm; overall: 50-66 µm.
It can be found in the plankton of mesotrophic, slightly acidic, waters.

References: 
Coesel, P.F.M. (1996) The Dutch representatives of the Staurastrum manfeldtii complex (Desmidiaceae, Chlorophyta): a taxonomic revision.
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus.
West, W. (1892) A contribution to the freshwater algae of west Ireland.