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Pentagonia
P. maroccana, from Gauthier-Lièvre & Thomas, 1958

Genus Pentagonia Gauthier-Lièvre & Thomas, 1958

Diagnosis: Shape pyriform, in cross section polygonal with 3-5 lateral swellings sometimes terminating in a horn. Short (5-8 µm) collar, aperture circular, fundus with horn. Agglutinate shell composed of mineral particles as in Difflugia.

Ecology: Freshwater, sediments; Africa and Europa.

Two species:
P. maroccana Gauthier-Lièvre & Thomas, 1958
P. shablensis Todorov & Golemansky, 1998

Pentagonia
P. shablensis, after Todorov & Golemansky, 1998

Remarks
In 2021 I collected specimens of Difflugia mammillaris from the Gooimeer, a large lake in the Netherlands. These specimens had an irregular outline in top view, ranging from round, triangular to square (see below). The form of Pentagonia shablensis in particular raises the question of whether P. shablensis is a junior synomym of D. mammillaris and to what extent it is justified to maintain Pentagonia as an independent taxon.

Difflugia mammillaris
D. mammillaris, from Gooimeer, the Netherlands. Note the square contour in top view.
Difflugia mammillaris
Difflugia mammillaris
D. mammillaris, Gooimeer. Square (L) and triangular (R) contour in top view.

Original description of P. shablensis, from Todorov and Golemansky, 1998.

Pentagonia shablensis sp. nov.

Description. The shell is transparent, ovoid elongate, swollen in the mid-region but tapering at both extremities, to give a rounded protuberance aborally and gradually near the aperture, to give a slightly pronounced neck. There are three or four rounded longitudinal ribs which give a triangular or quadrangular shape of the shell in transverse section. It is composed mainly of small to medium flattish pieces of quartz so arranged that give a relatively smooth surface. The aperture is circulate and surrounded by mainly small particles of quartz.
Measurements (in um): n=23; Length 81-100; Width 52-65; Aperture 20-28; Length of collar 3-4; B/L 0.67+0,07
Remarks. This species is similar to P. maroccana Gauthier-Lievre & Thomas (1958), but may be distinguished from it by the absence of a clear pronounced aboral spine or horn and by the smaller and not curved collar. Furthermore, P. shablensis is distinct in having a larger ovoid shell with a more open aperture.
Etymology. This species is named after the area of Shabla lake in which it was found. New species for the Bulgarian protozoan fauna.

Difflugia mammillaris
Pentagonia shablensis, Bularia, from from Todorov and Golemansky, 1998.
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