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 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