Pleuropyge plana
Schrammen 1912
Pleuropyge plana has been described by Schrammen (1912) as a new species from Oberg (near Ilsede) and Biewende (near Wolfenbüttel). The species has not been reported from Höver previously and appears to be very rare at this locality.
The picture of Pleuropyge plana in Schrammen (1912) and the few fragments from Höver suggest a bilaterally compressed funnel shape rather than a compressed tube. Elongate parietal oscula are arranged along the narrow margins of the sponge. According to Schrammen (1912) Pleuropyge plana has a long stem, but pictorial evidence seems lacking.
The two specimens shown here were found together side by side, suggesting a more complex habit with a common axis or base, perhaps similar to a ship's propeller or a fan. The fragments are not totally plane but are slightly bent around their longitudinal axis, thus forming a concave and a convex side.
The ovate ostia are arranged in short radial furrows while the postica (see top left side of lower specimen) are closely spaced, circular and slightly more than one millimeter wide. The epirhyses and aporhyses seem slightly inclined towards the growth axis on the concave side and away from the growth axis on the convex side, i.e. the flat sides of the sponge, although similar at first sight, appear to be different.
Dictyonal skeleton composed of lychnisks, apparently not very regularly. Dermal and gastral sides with strong, but dissimilar cortex formations: On the outside, longitudinally arranged fused anaxial opaline fibres; interior surface composed of silica-mantled lychnisks.
Pleuropyge sp.
? new species
The specimen shown here from both sides was found in the Lower Campanian of Höver and appears to be a previously unknown form related to Pleuropyge plana. To date, only one specimen is known.
Pleuropyge sp differs from Pleuropyge plana by being incompletely compressed and by the (functionally related) lack of parietal oscula. The specimen shows a growth margin with a protruding wall on its convex side.
Compared to Pleuropyge plana, the ostia of Pleuropyge sp are less elongate, and furrows are only weakly developed near the base. The postica are smaller (approximately 0.5 to 0.7 mm) and separated by wider bridges.