Polyplacocystis ambigua (Penard, 1904)
Diagnosis: Periplast (20–50 μm in diameter) formed from scales with reticular external texture of distal surface. All scales bordered by a smooth or delicately ribbed rim. Scales are of three main shapes:
1) long, narrow fusiform scales with sharp-pointed apices ( Length: 7.68–14.16 μm; Breadth: 0.4–0.7; Width of rims: 0.09–0.26 μm;
2) narrowly ellipsoidal or naviculoid scales ( Length: 5.47–11.94 μm; Breadth: 0.95–2.09 μm; Width of rims: 0.11–0.33 μm;
3) broadly elliptical or oval scales with rounded poles ( Length: 3.67–9.22 μm; Breadth: 1.28–2.62 μm Width of rims: 0.14–0.38 μm).
Ecology: Freshwater, dry mosses. Not rare. Switzerland (type locality), Argentina, Canada, Chile, Germany, Japan, New Zealand, Sri Lanka, The Netherlands and Ukraine.