cell long, slender, slightly curved, middle almost straight
length 97–300 µm, width 4–8 µm
two chloroplasts, each with 3 longitudinal ridges
3–13 pyrenoids per cell
girdle bands absent, sometime pseudo girdle bands
cell wall smooth, colorless
apices slender, narrowly rounded, porus absent
terminal vacuole with one or two gypsum crystal
Closterium limneticum
I found Closterium limneticum in the plankton of the pond of the waste disposal companyConstance, which is highly eutrophic and has a high fish population. This agrees with the descriptions of the typical habitats of Closterium limneticum.
The characteristics of the specimens in my population match the criteria for Closterium limneticum. The cells are slightly curved, but almost straight in the central part. The cell wall is smooth and colorless (s. fig. 2 b). Each chloroplast contains 5–6 pyrenoids (s. fig. 1 a) and the terminal vacuoles each contain a large gypsum crystal. The apices of my specimens were tightly rounded, without a porus.
The similar species Closterium gracile has different ecological requirements and occurs mainly in nutrient-poor Sphagnum bogs. In addition, Closterium gracile has a clear thickening in the apices with a porus.
Fig. 1 a-b:Closterium limneticum. L = 273 µm. Two focal planes of a slightly squashed specimen. Obj. 60 X.
Fig. 2 a-b:Closterium limneticum. L = 273 µm. Two focal planes from the cell center. Note the smooth, transparent cell wall without a striation (b). Nu = nucleus, PY = pyrenoids. Obj. 100 X.
Fig. 3:Closterium limneticum. The apex of a semi-cell in detail. Note the single gypsum crystal (GC) in the terminal vacuole. The apex is narrowly rounded without a porus. Obj. 100 X.