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: 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.