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Description of CentropyxisTestate amoeba, test discoidal, flat, somewhat beret-shaped; dorsal surface rounded, ventral flat to concave; aperture ventral, may be circular to uneven but displaced towards one end; may be flattened at apertural end; fine spines may be present on edge, may be at one end only or all around the periphery; surface smooth, dorsally with many quartz grains and a little cement, ventrally polished-looking due to more cement and much smaller grains in test. Two widespread shell types. The first is bilaterally symmetrical, rounded, flattened more at front than at rear; ventral face flat; often spines at sides and rear; pseudostome: ventral, anterior, roundish, dorsal and ventral lips recurved, invaginated, often bridged from ventral margin to dorsal face of the test, shell can be organic or constructed with mineral particles or diatoms, shape, number of spines and size extremely variable, prefer freshwater habitats., for example, C. aculeate. The second form has a circular shell or elongated in ventral view, in lateral view oral region slightly flattened, aperture subterminal, only ventral lip incurved, no bridges from ventral to dorsal face, some are common in freshwater habitats and sphagnum most species of this group are found in drier mosses and humus. More than 130 species and many varieties have been described but many descriptions are not adequate. Type species: Centropyxis aculeata (Ehrenberg, 1838).