Cosmarium transitorium
(Heimerl) Ducellier, 1918
Most likely ID: n.a.
Synonym: n.a.
Sampling location: Schwemm Moor (Austria)
Phylogenetic tree: Cosmarium transitorium
Diagnosis:
- semi-cells almost hemi-spherical
- cells 1.5-1.6. times longer than wide
- length 60–80 µm, width 40–55 µm
- apices thickened
- cells wall punctate
- 2–4 pyrenoids per semi-cell
I have so far only found Cosmarium transitorium in the Schwemm Moor in Austria. The specimens of my population were mostly between 60–70 µm long and had only 2 pyrenoids per semi-cell. However, sometimes there can also be 4 pyrenoids per semi-cell. The cell wall is finely granulated and the apices are distinctly thickened.
Cosmarium transitorium can be confused with Cosmarium pachydermum and Cosmarium incrassum var. schmidlei. However, Cosmarium pachydermum does not have thickened apices and is significantly larger at 80–120 µm. Cosmarium incrassum var. schmidlei is also larger (80–100 µm) and has a central, smooth area without pores in the middle of the semi-cells.
Fig. 1 a-b: Cosmarium transitorium. L = 62 µm. Two focal planes of a specimen found in the Schwemm Moor. Note the thickened apices (arrow). Obj. 100 X.
Fig. 2 a-b: Cosmarium transitorium. L = 62 µm. The same specimen as shown in fig. 1 a-b in brightfield illumination. Obj. 100 X.