Centropyxis spinosa (Cash, 1905) Deflandre, 1929
Basionym: Centropyxis aculeata var. spinosa Cash, 1905
Synonym: Centropyxis bryophilus Dekhtyar, 1998
Diagnosis: Shell oval, with a neatly rounded anterior outline, purely chitinous, usually with relatively few adhering grains of sand, semitransparent; yellowish brown when young, gradually darkening with age, and sometimes partly or entirely covered with diatom frustules. Aperture usually oval, with the long axis parallel to the long axis of the shell, lobed or unequal in outline, variable in width, but always comparatively smaller than that of C. aculeata, the margin reversed and usually with two bridges connecting the invaginated aperture with the opposite dorsal area. Spines variable in number and also in length, of the same substance as the test, and often curved, with a plug in the aperture at the upper end. A broad ventral region around the aperture has a characteristic smooth and uniform structure that is clearly observable under SEM and light microscopy.
Dimensions: Cash (1905): 120—140 µm; Todorov and Bankov (2019): Length 107—136 µm; height 42—46 µm; spines 14—28 µm; aperture diameter 28—37 µm. My measurements: Length 91—117 µm; L/W ratio is 0.9—1.2; aperture 25—45 µm × 21—36 µm.
Habitat: In Sphagnum, or water bodies with Sphagnum contact.
Remarks: The lobed aperture is caused by the presence of two pillar-like internal bridges, and an anterior crescent-shaped connection between the ventral and dorsal regions, resembling a headphone (see images below).
