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Arcella conica
Arcella conica, 81 µm – stacked images

Arcella conica (Playfair, 1918)
Syn.: Arcella pyramidalis  Van Oye, 1926

Diagnosis: Test hemispherical; dorsal surface with angular facets which are bordered by six or more prominent folds; aperture slightly invaginated, circular and bordered by a collar.

Dimensions: In literature: diameter 68-100 µm; aperture 20-33 µm wide; my measurements: 49-98 µm.

Ecology: Freshwater.

Remarks: Variation in this species appears to be restricted to the arrangement of the angular folds. Specimens can be confused with A. costata, which has a flat apex. Playfair compares the shell in side view with a marquee-tent.

Arcella conica
Arcella conica, 80 µm in diameter – stacked images
Arcella conica
Arcella conica
Arcella conica
Arcella conica, 90 µm, stacked image
Arcella conica
Arcella conica
Arcella conica, Tirol, Austria
Arcella conica
Arcella conica, with long tapering pseudopods
Arcella pyramidalis
Arcella pyramidalis, after Van Oye, 1926
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