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Arcella gandalfi
Arcella gandalfi from Féres et al, 2016

Arcella gandalfi  Féres, Porfírio-Sousa, Ribeiro, Rocha, Sterza, Souza, Soares and Lahr, 2016

Diagnosis: Shell hemispherical with an apical cone in lateral view. The top of this conical extension is closed and presents a minor invagination. The top invaginated region is not always circular. These features give the shell a “funnel shape” which has not been reported in any other Arcella. Shell is circular in apertural view with a circular, central and invaginated aperture (pseudostome) with a small collar. Distinct marginal ring present (test brim) similar to Arcella brasiliensis, this feature is distinctive from the other Arcella species. Scanning Electron Microscopy (SEM) observations showed that the chitinous shell is made of small hexagonal alveolar units, however these units are elongated on the conical extension. Shell color varies from light yellow to brown.

Dimensions: Test diameter on average 81 μm, test height 71 μm, test border (1-2) 7 μm, test top invagination 3 μm, test top diameter 17 μm, brim width (1-2) 21 μm, aperture diameter 24 μm and aperture  height 5 μm. Test height has the largest range compared to others characters, ranging from 52 to 91, with standard deviation of 11.8.

Ecology: Freshwater, Brasil, in both still and running freshwater environments, presenting a range of ecological characteristics and environmental parameters. It seems that A. Gandalfi may occur in various trophic conditions, preferably in acid to neutral pH and in relatively high temperatures.

Arcella gandalfi
Arcella gandalfi, from Féres et al, 2016
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