Arcella vulgaris
Arcella vulgaris in lateral view

 

 

Arcella vulgaris Ehrenberg, 1830

 

Diagnosis: shell hemispherical, a distinct dome, evenly convex, with a distinct basal collar or rim; surface of dome may be undulated; height of test about one-half the diameter; surface smooth or with regular undulations; aperture invaginated, circular, and bordered by small lip; two vesicular nuclei.

 

Dimensions: in literature diameter 30-152 µm; diameter of aperture 22-32 µm. However, these measurements may cover a large range of specimens which were considered to be A. vulgaris and are therefore not reliable. My measurements:  80-150 µm, aperture 18-36 µm; ratio diameter of shell - aperture 0.2; ratio diameter - height 1.5-1.8.

 

Ecology: in the ooze and vegetation in stagnant water and also in soil, among algae and other plants.

 

Remarks: Probably to many shells have been labeled with the name "vulgaris", in the past but also still today. The problem is we don't know what species Ehrenberg really has seen, because his original description is to vague. A redescription will be needed.

 

Arcella vulgaris
Arcella vulgaris in dorsal view, with distinct basal border.
Arcella vulgaris
Arcella vulgaris
Shell diameter 122 µm, height 73 µm; D/H=1.7; Shell D 116 µm, H 76 µm D/H=1.5
Arcella vulgaris
Arcella vulgaris
Shell D 109 µm, H 72 µm D/H=1.5; Shell D 116 µm, H 74 µm D/H=1.6
Arcella vulgaris
These five shells were found in the same sample from the Naardermeer, the Netherlands. They differ slightly in height, diameter, shape and size of the basal rim and the invagination. The diameter-height ratio varies between 1.5 and 1.8. 1.6; Shell D 125 µm, H 69 µm D/H=1.8.
Arcella vulgaris
Arcella vulgaris, lateral view
Arcella vulgaris
Arcella vulgaris in lateral view
Arcella vulgaris
Arcella vulgaris
Arcella vulgaris in aboral view