world of amoeboid organisms


Aperture usually surrounded by pores. Aperture diameter 0.45 of shell diameter. Shell diameter 70-160 µm.

Aperture surrounded by pores. Aperture diameter ≥ 0.4 of shell diameter. Shell very flat; diameter 140-402 µm.

Aperture surrounded by pores. Distinct basal rim. Height ca 1/3 of shell diameter.

Shell elliptical, quadrate or circular. Shell often with distinct dorsal folds or ribs. Aperture small and with pores.       

A. conica

Shell with six or more ribs; dorsal surface with ribs and depressions; aperture smooth, without crenulations.

Arcella n. sp.
Shell with flattened top and aperture with crenulated border; usually with six ribs.
A. costata

Shell in side view trapezoid, with six or more ribs; aperture smooth without crenulations.


Shell in lateral view trapezoid, with 5-7 ribs. Aperture with pores.

A. intermedia

Shell with basal border. Dorsal surface with depressions. Diameter c. 80-110 µm.


Shell with basal border. Dorsal surface with depressions. Diameter c. 80 µm. 


Shell in lateral view hemispherical, with acute or somewhat rounded corners,  sometimes with a basal border. Diameter c. 35-55 µm. 

A. hemisphaerica

Shell hemispherical, with smooth and broad rounded corners in lateral view. 


Shell with distinct basal border. Ratio diameter aperture/shell 0.2.

Arcella crenulata
A. crenulata
Arcella crenulata

Shell dome shaped; aperture with irregular crenulated border.       

Arcella excavata
A. excavata

Shell formed like a saddle. Aperture elliptical.       

Shell balloon shaped.       

Test broader than high; height c. 80-90 µm.  

Shell with undulations, more or less spherical. 

Shell spherical, wrinkled.       
A. rukiensis


Shell shaped like an old hat.

Arcella formosa

Shell resembling a pie; prominent folds or ribs often with darker color.       

Arcella brasiliensis

Shell with striated border


Shell with a number of projections.


Shell border with numerous small spines.

Arcella multilobata


Shell flattened, with crenulated aperture.

A. corona


Shell crowned with some spines.


Shell with high dome and distinct neck.

Arcella gandalfi


Shell like Gandalf’s hat.


Shell sub-hemispherical, round smooth aperture, thickened edges

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