Shells in side view (left and right) and in frontal view (center). These shells came from a ditch with clay bottom near Montfoort, the Netherlands. All shells were c. 79-104 µm in length.

Difflugia balcanica  Ogden and Zivkovich, 1983
= D. biconcava Ertl, 1965 ?

Diagnosis: Shell ovoid or pyriform, with an aboral rounded cone or spine and laterally compressed; shell in lateral view with typical biconcave shape; aperture circular;  shell composed of a mixture of small to large pieces of mainly flattish quartz, arranged to give a relatively smooth surface.

Dimensions: Ogden and Zivkovich: 111-114 µm long, 79-82 µm broad, aperture 31 µm (n=2). My measurements: 78-104 µm (n=10).

Ecology: I found this species in sediment of a ditch near Montfoort, the Netherlands.

Remarks: When this species was described, Ogden and Zivkovic were, according to their remarks, unaware of the description of  D. biconcava Ertl, 1965 (“There does not appear to be any prior descriptions of any similar compressed species of Difflugia, and D. balcanica is considered to be distinct in having a leaf-like shape, with an angular surface and a pointed aboral extremity”). D. biconcava is a very similar, but larger species. Ertl: 100-143 µm long, 66-96 µm broad, aperture 29-32 µm. My measurements: Naardermeer 149-190 µm (n=8); nucleus 31-39 µm; (n=2). Probably both species are identical.

Difflugia balcanica
D. balcanica, published by Ogden and Zivkovic, 1983.
Difflugia biconcava
Difflugia biconcava, published by Ertl, 1965. This species is very similiar to D. balcanica, but larger (Ertl: 100-143 µm; my measurements 149-190 µm).
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