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

Arcella discoides

Arcella

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

 

 

Arcella arenaria

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

Arcella catinus

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

Arcella jurassica

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

Arcella gibbosa

Arcella

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

Arcella intermedia

Arcella

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

Arcella hemisphaerica

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

Arcella rotunda

Arcella
Arcella

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

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

Arcella spectabilis

Shell with undulations, more or less spherical. 

Arcella peruviana

Shell spherical, wrinkled.       

Arcella nordestina

 

Shell shaped like an old hat.

Arcella rukiensis

Arcella formosa

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

Arcella formosa

Arcella
Arcella

Shell with striated border

Arcella

Shell with a number of projections.

Arcella dentata

Arcella

Shell border with numerous small spines.

Arcella rota

 

Shell flattened, with crenulated aperture.

Arcella multilobata

 

Shell crowned with some spines.

Arcella rota

 

Shell with high dome and distinct neck.

Arcella apicata

 

Shell like Gandalf’s hat.

Arcella gandalfi

 

Shell sub-hemispherical, round smooth aperture, thickened edges

Arcella jeanneli

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