Zivkovicia compressa (Carter, 1864)
Diagnosis: test broad ovoid or pyriform, compressed in lateral view, with a short neck that joins the body in a V-shaped wedge; convex protuberances arise from each arm of the V-shaped wedge to give this species its characteristic shape; more or less rough surface composed of different sizes of sand- or quartz-grains arranged on an organic matrix; aperture circular or ovoid; internally at the junction of the neck with a perforated diaphragm, with two apertures.
Dimensions: Literature: length of shell 196-289 µm; my measurements: 130-280 µm.
Ecology: not rare in Sphagnum pools (Dwingeloo, Kortenhoef, Groeneveld - Baarn, Kootwijk, Loofles - Harskamp, all in the Netherlands)
Remarks: This species varies considerably in size and in the composition of the shell, often large particles are used to construct the shell and mask the characteristic outline of the convex protuberances.