ventral or dorsal view
side view
key characteristics
Arcella discoides
Arcella discoides

 

 

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

Arcella discoides

Arcella megastoma
Arcella megastoma

 

 

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

Arcella megastoma

Arcella artocrea
Arcella artocrea

 

 

 

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

Arcella artocrea

Arcella arenaria

 

 

 

 

 

Arcella arenaria

Arcella catinus
Arcella catinus

 

 

 

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

Arcella catinus

Arcella dentata
Arcella dentata

 

 

 

 

 

Shell with a number of projections

Arcella dentata

Arcella conica
Arcella conica

 

 

 

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.

Arcella costata
Arcella costata

 

 

 

 

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

Arcella costata

Arcella intermedia
Arcella gibbosa

 

 

 

 

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

Arcella gibbosa

Arcella gibbosa
Arcella intermedia

 

 

 

 

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

Arcella intermedia

Arcella hemisphaerica
Arcella hemisphaerica

 

 

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

Arcella hemisphaerica

Arcella hemisphaerica
Arcella rotundata

 

 

 

 

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

Arcella rotundata

Arcella vulgaris
Arcella vulgaris

 

 

 

 

 

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

Arcella vulgaris

Arcella crenulata
Arcella crenulata

 

 

 

 

 

Shell dome shaped; aperture with irregular crenulated border.

Arcella crenulata

Arcella excavata
Arcella excavata

 

 

 

 

 

Shell formed like a saddle. Aperture elliptical.

Arcella excavata

Arcella mitrata
Arcella mitrata

 

 

 

 

 

Shell balloon shaped.

Arcella mitrata

Arcella robusta formosa
Arcella robusta

 

 

 

 

 

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

Arcella formosa

Arcella discoides
Arcella discoides

 

 

 

 

 

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

Arcella spectabilis

 

 

 

 

 

Shell with striated border

Arcella brasiliensis

 

 

 

 

 

 

Shell border with numerous small spines

Arcella rota

 

 

 

 

 

Shell with undulations, more or less spherical

Arcella peruviana

 

 

 

 

 

 

Shell spherical, wrinkeled

A. nordestina

 

 

 

 

 

Shell shaped like an old hat

A. rukiensis

 

 

 

 

 

 

Shell crowned with some spines

A. corona

 

 

 

 

 

Shell crowned with some spines

A. apicata

 

 

 

Shell like Gandalf's hat

A. gandalfi