Difflugia balcanica Ogden & Zivkovich, 1983
= D. biconcava Ertl, 1965 ?
Diagnosis: The shell is ovoid or pyriform, with a rounded cone or spine at the aboral end, and is laterally compressed. In lateral view, the shell exhibits a typical biconcave shape. The aperture is circular. The shell is composed of a mixture of small to large, mainly flat quartz pieces, arranged to create a relatively smooth surface.
Dimensions: Ogden and Zivkovich (1983): Shell length 111-114 µm long; 79-82 µm broad; aperture 31 µm (n=2). My measurements: 78-104 µm (n=10).
Ecology: Freshwater. In sediment of a ditch near Montfoort, the Netherlands.
Remarks: When this species was described, Ogden and Zivkovic, according to their notes, were unaware of the description of D. biconcava Ertl, 1965. They stated: “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”. However, D. biconcava is a very similar, albeit larger species. Ertl reports: Length 100-143 µm; width 66-96 µm; aperture 29-32 µm. My measurements from Naardermeer: 149-190 µm (n=8); nucleus 31-39 µm (n=2). It is likely that both species are identical.
