Difflugia viscidula Penard, 1902 pars
Diagnosis: shell elongated oblong, usually with a distinct neck, composed of much smaller particles than the rest of the shell; with zoochlorellae.
Dimensions: Penard (1902): 180-260 µm; my measurements: length 222-460 µm (mean 365 µm); width 118-200 µm; aperture 56-101 µm.
Ecology: fresh water; Switzerland; the Netherlands (Naardermeer and several other locations).
Remarks: Penard described this species in 1902 as D. viscidula, but in 1905 he wrote that he had made a mistake by which he thought that D. lemani was a much smaller species. He noticed erroneously 31-80 µm, instead of 180-310 µm, as given by Blanc (1892). However, he gives three different drawings (see below). No 1 and 2 seem to be the same as described by Blanc, but no 3 is different by having a clear neck. I have found both types and I think that there are at least two different species. The oblong (acorn) type and the elongated one with the neck.