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Arcella arenaria
Arcella arenaria

Arcella arenaria  Greeff, 1866

Diagnosis: shell always circular in apical view, more or less dome-shaped in lateral view; dorsal surface usually with slight folds, but very often flattened. Shell yellowish brown to dark brown in color. Aperture small, circular in shape, its diameter barely reaching 1/5-1/6 that of the shell. Many small pores, 8-28 in number, around the aperture. Height of the shell not less than 1/2 diameter of the shell. Neither remarkable border nor bosses around the lateral margin. Many nuclei present: the large ones usually 3 in number and arranged in an equilateral triangle, the small ones not constant in number, varying 3-5, arranged irregularly. The pseudopodia very short, 6 at most, many vacuoles developing along the ectoplasm.

Dimensions: In literature shell 75-130 µm in diameter, 21-50 µm in height, aperture 12-28 µm in diameter, pores 8-18.

Ecology: Mostly in dryer mosses; on Hypnum and Polytrichum, also on lichens on trees and between Sphagnum.

Remarks: This species resembles Arcella catinus Penard; it can also be confused with Arcella artocrea. The folding of the dorsal surface is most distinct in lateral view.
This species seems easily to identify.

Arcella arenaria
Arcella arenaria
Arcella arenaria
Arcella arenaria
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