Stauridium tetras
(Ehrenberg) E.Hegewald, 2005
Most likely ID: n.a.
Synonym: Pediastrum tetras
Sampling location: Pond of the convent Hegne, Pond of the waste disposal company Constance, Ulmisried, Simmelried
Phylogenetic tree: Stauridium tetras
Diagnosis:
- coenobium star-shaped, flat and single layered
- diameter coenobium up to 55 µm
- coenobium of (4)–8–16–32–(64) cells
- cell wall smooth
- each cell with two lobes with each two short projections
- marginal cells with V-shaped incision
- inner cells with narrow incision
- without intercellular spaces
- single pyrenoid per cell
I find Stauridium tetras in my sampling sites both in plankton and in the growth on aquatic plants and wood. However, the species is not very common in my sampling sites.
The species was describes as Pediastrum tetras and transferred to the new genus Stauridium in 2011 by Hegewald.
The coenobia in my population mostly consist of 8 cells and are quite small (approx. 30–35 µm). Only very rarely do I find coenobia with 16 cells (s. fig. 2) and I have never found coenobia with 32 or 64 cells.
The coenobia have no intercellular spaces and the cells touch each other. The marginal cells each have a total of 4 short processes, which are sometimes only warty or not present at all (s. drawing 2, above). The marginal cells have a V-shaped incision, whereas this is only slit-shaped in the inner cells. The cell wall is completely smooth.
Fig. 1 a-b: Stauridium tetras. D = 36 µm (of coenobium). Two focal planes of a coenobium of 8 cells. Note the smooth cell wall (b). Obj. 100 X.
Fig. 2: Stauridium tetras. D = 43 µm (of coenobium). A coenobium of 16 cells. Note the V-shaped incisions (arrows) of the marginal cells. PY = pyrenoid. Obj. 100 X.