Difflugia acuminata
Difflugia acuminata: left to right: 293 µm, 330 µm, 333 µm (drawing after Ehrenberg, 1838)

Difflugia acuminata Ehrenberg, 1838

Diagnosis: shell long, cylindrical, slightly tapering from the posterior to the anterior end; posterior end pointed or with a more or less long, hollow and open tube or spine; shell composed of mineral grains, more or less mixed with scales of diatoms; in sphagnum the test can be completely composed of diatoms; aperture circular.

Dimensions: In his original description Ehrenberg gives a length of 1/3 mm = 333 µm. He describes the test as being oval oblong (see his drawing above).
The late Dr. A.A. de Groot (pers. comm.) has found shells in Baarn, the Netherlands, which were 800 µm large!

Ecology: Freshwater, all kind of water types, ranging from oligotrophic till eutrophic.

Remarks: Difflugia acuminata is probably a polymorphic species. Without doubt several variations of Difflugia acuminata has been described as new species. On the other hand the name covers probably several real species which are light microscopically hard to distinguish from the main morphotype. The most discriminating character is the shape en length of the spine, but in fact we don’t know precisely how variable it is. Shells with relatively long spines have been described as Difflugia giganteacuminata and with a curved spine as Difflugia curvicaulis.

Difflugia acuminata
Shells of Difflugia acuminata differ in shape, structure and size (180-390 µm)
Difflugia acuminata
Shells in a sample from Lemmer, Friesland, ranging from 204-429 µm. It shows the variability of this species.
Difflugia acuminata
These shells came from one sample (Kortenhoef) and varied in size from 214-364 µm. The first five specimen seems closely related, the other two tests are different.
 Difflugia acuminata
These shells came from another sample (Strabrechtste heide, Eindhoven), ranging from 239-322 µm.
Difflugia acuminata
Shells from a sample from Lemmer, Friesland, ranging from 180-253 µm
Five shells from the same sample, from Crailoo, measuring 270 to 415 µm
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