Difflugia acutissima

 

Five shells from the same sample; the fourth shell is in lateral view, with biconcave sides; the fifth shell shows two spines. 225-265 µm.

 

 

Difflugia acutissima Deflandre, 1931

 

Diagnosis: shell elongated ovoid with a short more or less distinct neck; fundus tapering into a sharp spine; shell composed of quartz particles, sometimes mixed with fragments of diatom shells; pseudostome circular.

 

Dimensions: Deflandre: length 178-233 µm; my measurements 210-265 µm (n>15).

 

Ecology: I found this species in sediments of a ditch in the nature reserve Naardermeer, the Netherlands. Some shells were compressed, with a biconcave shape, as characteristic for Difflugia biconcava, which lives in the same location.

 

Remarks: Deflandre in his description compares the shape with a truncated cigar. This species can be distinguished from Difflugia acuminata by its short distinct neck and the sharp tapering spine.

 

Difflugia acutissima
Difflugia acutissima, drawing by Deflandre, 1930
Difflugia acutissima, 234-258 µm

 

These shells were prepared by Penard and labelled as "Difflugia praestans" (image from Mazei and Warren, 2012). Just compare his shell b with the middle shell above this image. What's the difference? It shows how difficult it is to identify Difflugia species. Is D. acutissima a separate species or just a variation of D. praestans?