lateral margings almost straight, tapering to flat convex apices
shallow median constriction
length 30–50 µm, width 15–25 µm
cells 2–2.4 times longer than wide
chloroplasts star-shaped with irregular longitudinal ridges
one pyrenoid per semi-cell
cell wall punctae with 1–2 horizontal rows above isthmus
Actinotaenium cucurbita
I have only ever found Actinotaenium cucurbita in Sima Moor in June 2024. The species was common there. The specimen shown below has a length to width ratio of 2.12 and is therefore in the range of 2.0–2.4 indicated by Lenzenweger (1996). I could not exactly recognize the punctation of the cell wall in the living specimen. It is best visible in empty cells of dead specimens.
Fig. 1 a-b:Actinotaenium cucurbita. L = 35 µm. Two focal planes from the Sima Moor found in June 2024. Obj. 40 X.