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.