Paramphitrema rhenanum (Lauterborn, 1896)
Diagnosis: Shell a thin membrane, oval to spindle-shaped, often somewhat irregular, at both poles tapering to a small tubular aperture. Shell surface covered with very minute mineral grains, which are more dense and numerous at both poles; cytoplasm specially in the central area densely filled with minute red granules, just as in the rotosphaerid Pinaciophora fluviatilis Greeff. Nucleus centrally, vesicular, spherical with large nucleolus. In locomotion clots of plasma come through the apertures and form a single thin sharply pointed pseudopodium, which often bends arch-shaped or more or less in a sharp knot.
Dimensions: Length of shell 40-45 µm, width 10-15 µm.
Remarks of Lauterborn (1908): "So far only in the diatom mud of the Rhine, together with Hyalosphenia Penardi Lauterborn, Pinaciophora fluviatilis Greeff, etc., always separately. In 1903 Penard has described from Lake Geneva, under the name of Amphitrema lemanense a rhizopod, which shows an extremely extensive similarity with A. rhenanum, even the red granules inside are present. A difference should be after Penard that his A. lemanense is slightly compressed, in cross-section more elliptical. Further the dimensions were around 20-35 µm for the shells from Lake Geneva, against 40-45 µm for those from the Rhine. I must confess that I think such minute differences in the quite variable rhizopod bowls so insignificant, that I would personally not even dare to justify even only a variety."