Centropyxis spinosa Cash, 1905
(Centropyxis aculeata var. spinosa Cash 1905)
Diagnosis: Test purely chitinous, usually without adherent sand-grains, semi-transparent; yellowish brown when young, turning to a darker brown with age (like Arcella vulgaris), and often partially or wholly covered with diatom- frustules. The mouth lobate or of unequal outline, variable in width, but always relatively small compared with C. aculeata, the margin sometimes slightly inverted. Spines variable in number and also in length, of the same substance as the test, and frequently curved.
Dimensions: Cash: 120-140 µm; other literature: shell 97-127 µm in diameter.
Ecology: in sphagnum, other mosses, in the ooze of ditches and lakes.
Remarks: Cash (1905) suggested that this species differs from C. aculeata in the structure of the shell, being delicate, more compressed, with more spines and having a lobate aperture. This species appears to vary like C. aculeata in the number of spines and the size of the shell, but is distinguished by the internal extensions of the aperture. Cash: "This variety seems to have been regarded by most observers as indistinguishable from the type. We are, however, of opinion that the structure of the test, its more numerous spines and particularly the lobate mouth, are characters which justify the separation of this form under a varietal name. In our experience it most frequently occurs in wet Sphagnum. The variety is further distinguished from the type by its being more compressed and altogether more delicate in appearance."
Probably C. spinosa is part of the C. aculeata morphotype.