Centropyxis discoides (Penard, 1902) Deflandre, 1929
Basionym: Centropyxis aculeata var. discoides Penard, 1890
Diagnosis: Shell usually more or less circular in outline, sometimes strongly deformed, strongly flattened, dish shaped, with 0-9 hollow spines in the fundus area; shell composed of a granular organic material, embedded with some xenosomes, but never completely covered; most xenosomes in the fundus area; aperture sometimes nearly central, irregular or lobed, with (usually) 4 small bridges connecting the invaginated apertural border to the inner dorsal surface. One single granular nucleus.
Dimensions: 135-320 µm (also with spines included). My measurements: 159-286 µm (without spines).
Ecology: Freshwater. On aquatic plants and in sediment. Probably cosmopolite.
Remarks:This is a large species, on average about 250 µm, with a relatively flat shell compared to other Centropyxis species. Smaller specimens can easily be confused with C. aculeata, a species that has not been sufficiently typified. Originally, C. discoides was described by Penard (1890) as a variety of A. aculeata. C. discoides is a large species with relatively flat skin compared to other Centropyxis species. Smaller specimens can easily be confused with C. aculeata, a species that is not sufficiently typified. The image below shows variation in shell shape and structure between some specimens from the same location. It is quite possible that deviant forms have been described as new species or varieties in the past, e.g., C. aculeata var. grandis Deflandre, 1929, and C. discoides var. grandistoma Chardez, 1966.