Cosmarium caelatum Ralfs, 1848
Most likely ID: n.a.
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Synonym: n.a.
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Sampling location: Ibmer Moor (Austria), Schwemm (Austria)
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Phylogenetic tree: Cosmarium caelatum
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Diagnosis:Â
- semi-cells broadly trapezoidal with flattened apex
- length 40–50 µm width 36–40 µm
- sinus narrow, slightly dilated to the isthmus
- apical margins of semi-cells regularly indented between granulated crenellations
- radially arranged groups of warts become smaller towards the center of the semi-cells
- ornamentation of central field variable, often with elongated, warts arranged in parallel
- one pyrenoid per semi-cell
I found Cosmarium caelatum in June 1995 in the Ibmer Moor in Austria and in 2026 in the Schwemm (Austria). Although this species is described by Lenzenweger (1999) as common and adaptable, I have only been able to find it very rarely and with large temporal intervals.
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The semi-cells of Cosmarium caelatum are richly ornamented, which makes it look attractive by light microscopy. The semi-cells are mostly trapezoidal with flat apices. Separate groups of warts arranged radially run from the margins of the semi-cells toward the center of the cell and become smaller. The design of the central field of the semi-cells is variable, but always characterized by symmetrically arranged groups of warts. Often elongated, warts arranged in parallel dominate the center of the semi-cells, as in my specimen (s. figs. 1 a and 2 a), which corresponds most closely to drawing 3 (s. drawings above).
Fig. 1 a-b: Cosmarium caelatum. L = 52 µm. Two focal planes of a slightly squashed specimen found in 1995 in the Ibmer Moor. Note the radially arranged groups of warts becoming smaller towards the center of the semi-cells (arrows). Obj. 100 X.
Fig. 2 a-b: Cosmarium caelatum. L = 46 µm. A second specimen found in June 2026 in the Schwemm Moor (Austria). Obj. 100 X.