Difflugia lithoplites Penard, 1902
Diagnosis: Test spherical, often like a perfect ball, colorless to brown, sometimes very dark, composed of mineral grains and diatom frustules, bound together by an organic cement. No collar present. Aperture with an uneven outline, with three or four sharp grains which give the impression of teeth. Test with or without some small hollow spines, straight or s-shaped curved, often with a small mineral piece in the opening, hence the name ‘lithoplites’. Nucleus large, granular.
Dimensions: Penard diameter of test 200-220 µm, nucleus 65-70 µm. My measurements: 128-248 µm, mean 199 µm; nucleus 44 µm.
Ecology: Freshwater. On sediment and aquatic plants or between filamentous algae; common in mesotrophic waters with Sphagnum contact; not seldom together with Difflugia corona and Difflugia capreolata.
Located in Het Hol (Kortenhoef), Naardermeer, Bert Bospad (Loosdrecht) and Strabrechtse Heide (Eindhoven).
Remarks: Approximately 50% of the specimens don’t have spines. The test crashes easily under the pressure of the cover glass.
A remarkable fact is the presence of very small pieces of quartz in the opening of the spines. Its function is not known. This fact has been described by Penard (1902), see his drawings below, and it shows what a great observer he was!