Porosia bigibbosa (Penard, 1890)
Diagnosis: Shell colorless or yellowish, laterally compressed (about 2 : 1), pyriform with a broad, slightly convex aperture. In broad lateral view, at approximately one third of the body length from the aperture, there are two large pores, located in lateral depressions. Shell composed of oval, circular or elongate shell plates of different sizes. Aperture oval, concave in narrow lateral view, surrounded by a distinct organic collar.
Dimensions: Length 135-170 µm, Width 87-110 µm; my measurements 118-144 µm.
Ecology: Mosses and soil. Todorov (2002) found abundant shells in beech litter in Bulgaria. He suggested that P. bigibbosa is not a typical inhabitant of Sphagnum mosses but is closely related to the litter of deciduous forests (mainly beech forests) and can be used as an indicator species for these biotopes. I found living specimens in moss on rocks in a beech wood near Saarburg, Germany.
Geographical distribution: British Isles, Bulgaria, Canada, Chile, France, Germany, Greece, Java, Nepal, Philippines, Spitsbergen, Switzerland, Thailand (Todorov, 2002)