Aperture usually surrounded by pores. Aperture diameter 0.45 of shell diameter. Shell diameter 180 µm.

Arcella discoides

Aperture surrounded by pores. Aperture diameter ≥ 0.4 of shell diameter. Shell very flat; diameter 180 µm.

Arcella megastoma

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

Arcella artocrea

 

 

Arcella arenaria

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

Arcella catinus

 

Shell with a number of projections.

Arcella dentata

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

Arcella conica

 
Shell with flattened top and aperture with crenulated border; usually with six ribs.

Arcella n.sp.

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

Arcella costata

 

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

Arcella gibbosa

 

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

Arcella intermedia

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

Arcella hemisphaerica

 

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

Arcella costata

 

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

Arcella vulgaris

 

Shell dome shaped; aperture with irregular crenulated border.       

Arcella crenulata

 

Shell formed like a saddle. Aperture elliptical.       

Arcella excavata

 
Shell balloon shaped.       

Arcella mitrata

 

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

Arcella formosa

 

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

Arcella spectabilis

 

Shell with striated border

 

Shell border with numerous small spines.

Arcella rota

 

Shell with undulations, more or less spherical. 

Arcella peruviana

 
Shell spherical, wrinkled.       

A. nordestina

 

Shell shaped like an old hat.

A. rukiensis

 

Shell crowned with some spines.

Arcella rota

 

Shell with high dome and distinct neck.

Arcella rota

 

Shell like Gandalf’s hat.

A. gandalfi

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