Cylindrifflugia acuminata

Cylindrifflugia acuminata: left to right: 231 µm, 330 µm, 333 µm (drawing after Ehrenberg, 1838)

Cylindrifflugia acuminata (Ehrenberg, 1838) González-Miguéns et al., 2022
Basionym: 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: According to Ehrenberg (1838): Shell length 333—375 µm.
In his original description Ehrenberg gives a length of 1/3 mm = 333 µm and in the Latin description a length of 1/6 Linie = 375 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!

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

Remarks: Cylindrifflugia acuminata is probably a polymorphic species. Without doubt several variations of C. acuminata have been described as new species. On the other hand, the name likely encompasses several distinct species that are difficult to distinguish from the main morphotype using light microscopy. The most distinguishing characteristic is the shape and length of the spine; however, we do not precisely know how variable it is. Shells with relatively long spines have been described as Difflugia giganteacuminata, while those with a curved spine have been identified as Difflugia curvicaulis,

First mention of C. acuminata by Ehrenberg, 1830.

Original description of C. acuminata, Ehrenberg, 1838.

Shells of C. acuminata (226—243 µm). Shells from a pond in the Odenwald, Hessen, Germany, 2024.

Shells of C. acuminata (217—237 µm). All shells from a pond in the Odenwald, Hessen, Germany, 2024.

Below, a number of shells are depicted that bear a strong resemblance to the shells above. It is quite possible that these represent different species. It is also possible that environmental factors play a role in the various appearances.

Shells resembling C. acuminata (the shell on the left) vary in shape, structure, and size (180–390 µm). All shells were collected from different locations in the Netherlands.

Shells in a sample from Lemmer, Friesland, ranging from 204—429 µm. It shows the variability of this species.

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.