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Difflugia biconcava
D. biconcava, 157 µm long, in front view and lateral view – Naardermeer

Difflugia 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. Nucleus spherical with large central nucleolus which contains a number of lacunae.

Dimensions: 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; Montfoort 78-104 µm. This is an extremely variable species.

Ecology: Ertl found the type material in samples from rice fields in Slovakia. I found this species in sediments of a ditch near the Naardermeer, the Netherlands.

Remarks: D. balcanica Ogden and Zivkovich, 1983 is a very similar, but much smaller species. Ogden gives as length 111-114 µm and as breadth 79-82 µm (n=2).

Difflugia biconcava
Difflugia biconcava, in frontal and lateral view – after Ertl, 1965 (left) and from Naardermeer, 2015 (right).
Difflugia biconcava
Difflugia biconcava, in lateral view (upper row) and frontal view (lower row. All shells came from the same sample and were alive. Notice the right one with two cones. Length 161 – 185 µm.
Difflugia biconcava
Difflugia biconcava, published by Ertl, 1965
Difflugia balcanica
D. balcanica, published by Ogden and Zivkovic, 1983. This species is very similiar to D. biconcava, but much smaller: 111-114 µm.
Difflugia biconcava
Difflugia biconcava
Difflugia biconcava, stacked image, shell 190 µm, Naardermeer
Difflugia biconcava
Difflugia biconcava
Difflugia biconcava, nucleus and pseudostome (Naardermeer)
Difflugia biconcava
Two dividing cells, note the difference in size between them.
Difflugia biconcava
Difflugia biconcava
Difflugia biconcava, the same test in frontal and in lateral view.
Difflugia biconcava
Difflugia biconcava
Difflugia biconcava
Difflugia biconcava
Difflugia biconcava, pseudopodia
Difflugia biconcava
Difflugia biconcava, in frontal and lateral view – after Ertl, 1965 (left) and from Naardermeer, 2019 (right).
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