Closterium directum Archer, 1862

Most likely ID: n.a.

 

Synonym: n.a.

 

Sampling location: Schwemm Moor (Austria)

 

Phylogenetic tree: Closterium directum

 

Diagnosis: 

  • cells slender, slightly curved, straight in middle
  • tapered slightly towards ends
  • length 195–450 µm
  • cell wall with tight striation (9-10 striae/10 µm)
  • striation of cell wall sometimes absent
  • girdle bands present
  • chloroplast with 3–6 longitudinal ridges
  • 6–19 pyrenoids per semi-cell
  • apices subtruncate, broadly rounded, pore absent
  • terminal vacuoles with aggregates of crystals
Closterium-directum
Closterium directum
So far, I have only found Closterium directum in the Schwemm Moor, where this species is very common. Closterium directum can essentially be recognized by the very slightly curved cells, which hardly taper towards the apices (s. fig. 1 a-b). The apices are very broadly rounded or almost flat. The cell walls in the specimens of my population were always distinctly striated (s. fig. 4). However, Förster (1982) mentions that the striation can also be very weak or even absent. In the terminal vacuoles of this species, there are always aggregates of crystals, which can appear stacked (s. fig. 5 a).
Closterium-directum

Fig. 1 a-b: Closterium directum. L = 222 µm. Two focal planes of a specimen in DIC. Obj. 60 X.

Closterium-directum

Fig. 2 a-b: Closterium directum. L = 222 µm. The same specimen as shown in fig. 1 a-b in brightfield illumination. Obj. 60 X.

Closterium-directum

Fig. 3 a-b: Closterium directum. L = 374 µm. A second, larger specimen. Obj. 60 X.

Closterium-directum

Fig. 4: Closterium directum. L = 222 µm. The striation of the cell wall in a squashed specimen. GB = girdle bands. Obj. 100 X.

Closterium-directum

Fig. 5 a-b: Closterium directum. Two focal planes of the broadly rounded apex without pore. The terminal vacuole (TV) is filled with aggregates of crystals. Obj. 100 X.

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