Difflugia giganteacuminata (Chardez, 1958) Chardez et Gaspar, 1984
Most likely synonymous with D. acuminata Ehrenberg, 1838
Diagnosis: Shell nearly cylindrical, always longer than 350 µm and with a large and long spine, which is at least 1/4 of the shell length.
Dimensions: Chardez & Gaspar (1984): 360-550 µm, spine 87-100 µm. My measurements: 419-468 µm.
Ecology: Sediment of ditches, between water plants.
Remarks: Chardez designed this variety in 1958 because of its larger length compared to D. acuminata, using the average length of 200 µm given by Penard for D. acuminata. However, the length in the original description of D. acuminata is 333-375 µm (see my comments on D. acuminata). Chardez indicates a length of 400-650 um for his variety. This is not really different from the length given by Ehrenberg (1938). D. acuminata can vary a lot in size, see the pictures below as an example. In 1984, the variety is promoted by Chardez and Gaspard to species level and is named D. giganteacuminata. They give a length of 360-400 microns, excluding the long horn.
Based on my own observations, I don’t think that D. giganteacuminata is a separate species, not even a variety of D. acuminata. Further observations are needed to make this clear. Just look at the rows of shells below. They come from different locations. The second one in the second row could be identified as D. giganteacuminata, if it was found without the other shells. It measures 429 µm. The same is true for shells in the other rows.