Placocista glabra Penard, 1906

Diagnosis: Test medium‑sized, strongly compressed, regularly elliptical in dorsal view with only a slight difference between major and minor axes (ratio approx. 5:4). Anterior end truncated to form a very narrow slit‑like pseudostome, sometimes appearing denticulate at the lateral commissures. In sagittal view the test resembles a biconvex lens.

Siliceous plates large, elongated‑elliptical with one margin slightly truncated, giving a rhomboid appearance. Near the pseudostome the plates become broader and more rounded; the outermost peristomal plates may be wider than long. Plates are perfectly smooth and never denticulate; any apparent denticulation in lateral view is an optical effect caused by overlapping plate edges. The marginal ridge is formed by the meeting of the lateral plates at an acute angle, often irregular due to imperfect alignment. No spines or needles occur anywhere on the shell, which is completely smooth.

Plasma filled with numerous small yellowish granules; one or several contractile vacuoles usually present near the pseudostome. Nucleus large, pale, containing 1–4 rounded nucleoli positioned superficially.

Dimensions: Penard (1906): Length: 84–105 µm; Width: not explicitly given, but proportional to the 5:4 ellipse ratio.

Ecology: Collected in a small peat bog (“la Pile”), exclusively in Sphagnum. The species occurred only in one very restricted tuft of Sphagnum, where it co‑occurred with Placocysta spinosa and P. jurassica. Despite repeated sampling throughout the bog, it was never found outside this single patch, indicating a highly localized and specific microhabitat preference within Sphagnum peatlands.

Distribution: Known from Switzerland.