Cosmarium carniolicum
(Lütkemüller) Kouwets, 2025
Most likely ID: n.a.
Synonym: Cosmarium pseudopyramidatum var. carniolicum
Sampling location: Paradieswiesen (Austria)
Phylogenetic tree: Cosmarium carniolicum
Diagnosis:
- semi-cells truncate-pyramidates
- lateral margins slightly concave
- length 48–60 µm, width 20–23 µm
- sinus deep, straight, internally dilated
- cell wall smooth, punctate
- one pyrenoid per semi-cell
Cosmarium carniolicum was originally described by Lütkemüller (1900) as Cosmarium pseudopyramidatum var. carniolicum. It was not until 2025 that Kouwets elevated it to a separate species.
I found Cosmarium carniolicum for the first time in June 2024 in the Paradieswiesen in Austria. This Cosmarium species is quite inconspicuous in samples, as it is relatively small at approx. 50 µm and has no striking shape or ornamentation. It is much more similar to Cosmarium pseudopyramidatum. However, this species is slightly larger (approx. 70 µm) and its lateral margins are convex, whereas those of Cosmarium carniolicum are slightly concave (s. fig. 1 a).
Fig. 1 a-b: Cosmarium carniolicum. L = 48 µm. Two focal planes of a specimen found in the Paradieswiesen (Austria). Note the concave lateral margins (arrows), what is characteristic for the species. Obj. 100 X.