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Centropyxis discoides
Centropyxis discoides, 231 and 245 µm wide

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.

Centropyxis discoides
Centropyxis discoides
Centropyxis discoides
Shell in lateral (L) and dorsal view (R); the arrows indicate the position of the four bridges.
Centropyxis discoides
C. discoides, after Penard (1902)
Centropyxis discoides
Some specimens collect a lot of debris around their shell.
Centropyxis discoides
Centropyxis discoides
Centropyxis discoides
Centropyxis discoides
Nuclei
Centropyxis discoides
Centropyxis discoides
C. discoides, both from the same sample, on submerged plants in lakes near Kortenhoef, Netherlands
Centropyxis discoides
Centropyxis discoides
Specimen (235 µm) from Crailoo
Centropyxis discoides
Centropyxis discoides
C. discoides, 286 and 260 µm, both from the same sample, ditch in ‘s-Graveland, Netherlands
Centropyxis discoides
Centropyxis discoides
C. discoides, 225 and 245 µm in diameter, Crailoo, Netherlands
Centropyxis discoides
C. discoides, side view, 253 µm in diameter
Centropyxis discoides
C. discoides, without spines, feeding on an algae
Centropyxis discoides
C. discoides, with 9 spines – Laegieskamp
Centropyxis discoides
C. discoides, 226 µm, with 8 spines – Laegieskamp
Centropyxis discoides
Centropyxis discoides, 196 µm – Naardermeer
Centropyxis discoides
C. discoides, 235 µm
Centropyxis discoides
C. discoides, 224 µm – Crailoo
Centropyxis discoides
C. discoides, 248 µm – Lagieskamp
Centropyxis discoides
C. discoides, 245 µm – Naardermeer
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