Cosmarium dickii Coesel, 1989
Most likely ID: n.a.
Synonyms: Cosmarium blyttii f. bipunctatum, Cosmarium blyttii var. bipunctatum, Cosmarium blytii var. bipunctatum
Sampling location: Simmelried
Phylogenetic tree: Cosmarium dickii
Diagnosis:
- semi-cells rounded rectangular
- length 20–24 µm, width 19–23 µm
- apices flat with weak undulations
- lateral margins with undulations
- intramarginal with 2 rows of small granules
- a pair of distinct granules at base of each semi-cell
- one pyrenoid per semi-cell
- sinus deep and narrow, dilated at outside
- isthmus 6–7 µm wide
Cosmarium dickii is a small, inconspicuous species that I have only found in the Simmelried so far. Its most important distinguishing features are its almost rectangular semi-cells with undulated margins and a pair of warts at the base of each semi-cell (s. fig. 1 b).
The similar species Cosmarium didymochondrum also has undulated margins and a pair of warts at the base of the semi-cells, but this species is about twice as large (41–50 µm) and the semi-cells are approximately semicircular.
Fig. 1 a-b: Cosmarium dickii. L = 26 µm. Two focal planes of a slightly squashed specimen. Note the pair of granules at the base of the semi-cells (arrows). Obj. 100 X.