Arcella conica, 81 µm – stacked images
Arcella conica (Playfair, 1918)
Syn.: Arcella pyramidalis Van Oye, 1926
Diagnosis: Shell 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.
Habitat: Freshwater.
Geographical distribution: Probably cosmopolitan.
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, 80 µm in diameter – stacked images
Arcella conica
Arcella conica, 90 µm, stacked image
Arcella conica, Tirol, Austria
Arcella conica, with long tapering pseudopods
Arcella pyramidalis, after Van Oye, 1926