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Zivkovicia compressa
Zivkovicia compressa, living specimen with test filled with protoplasm.

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: Freshwater; 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.

Zivkovicia compressa
Diaphragm with two apertures as seen through the pseudostome.
Zivkovicia compressa
Zivkovicia compressa
Aperture visible through the pseudostome
Zivkovicia compressa
A large piece of quartz acts as a window, showing the edge of the diaphragm (arrows), composed of small mineral grains.
Zivkovicia compressa
Zivkovicia compressa, with a very thin edge of the diaphragm visible at the lower right part
Zivkovicia compressa
Zivkovicia compressa – stacked image
Zivkovicia compressa
Zivkovicia compressa, 234 µm, right: the bridge as viewed through the aperture.
Zivkovicia compressa
Zivkovicia compressa, 234 µm and another species, 130 µm, both from the same location
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