Arcella vulgaris – Microworld

Arcella vulgaris in lateral view

Arcella vulgaris Ehrenberg, 1830

Diagnosis: Shell hemispherical, helmet-shaped, with a distinct basal edge; height of the shell about one-half the diameter. Surface smooth; aperture invaginated, circular, with recurved collar; cytoplasm with epipodia attached to the shell; usually with two vesicular nuclei.

Dimensions: In literature the diameter is 100-152 µm; diameter of aperture 22-32 µm. My measurements: 80-150 µm, aperture 18-36 µm; ratio shell diameter/aperture = 0.2; ratio diameter/height = 1.5-1.8.

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

Remarks: Probably too many shells have been labeled with the name “vulgaris”, in the past but also still today. The problem is that Ehrenberg’s description is too broad. It says, translated from French:

Orbicular bell-shaped, often hemispherical or swollen on the back, with a smooth shell made up of very small grains stuck in regular series, yellow or reddish brown.

Arcella vulgaris, from Ehrenberg, 1830

Arcella vulgaris, from Ehrenberg, 1838

A. vulgaris, with basal border.

Arcella vulgaris in lateral view

A. vulgaris, from the same population as above, without distinct basal border.

A. vulgaris in lateral view, from Deflandre, 1928

A. vulgaris, from the same population as above, with six nuclei.

Arcella vulgaris in dorsal view, with distinct basal border.

Shell diameter 122 µm, height 73 µm; D/H=1.7; Shell D 116 µm, H 76 µm D/H=1.5

Shell D 109 µm, H 72 µm D/H=1.5; Shell D 116 µm, H 74 µm D/H=1.6

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.