Pleurope lacunosa
F.A.Roemer, 1841
Pleurope lacunosa occurs rarely at Misburg and Höver. Previously, only the stems of Pleurope lacunosa were known and were actually mistaken for the sponge itself. The specimen shown here, although incomplete, reveals the true nature of Pleurope lacunosa.
Pleurope lacunosa has a flat, scabbard-like stem with large oval openings (parietal oscula) along its narrow margins. However, approximately at half-height of the sponge, the stem widens to form a longitudinally folded funnel with a trumpet-shaped top. The inward-facing longitudinal folds of the lower funnel section turn into a set of pronounced radiating arched ribs. The outward-facing longitudinal folds of the lower funnel section grade into the flat sectors between the ribs.
The height of the specimen is 210 mm, the original diameter of the funnel was approximately 120 mm; the ribs are approximately 6 to 7 mm thick; the wall thickness is 1 mm at the outer rim.
The following pictures show some fragments of Pleurope lacunosa which give additional details.
The first picture shows a stem section viewed from its wide and narrow side. The parietal oscula of this particular specimen are rimmed by a conspicuously strong margin.
The next three images show specimens considered to represent upper parts of Pleurope lacunosa, in side-, bottom-, and side-view, respectively.
Contrary to many other sponge species, Pleurope lacunosa has no branching roots. The basal parts shown here apparently penetrated other objects to obtain some anchorage.
However, the specimen shown first on this page reveals tufts of siliceous fibres radiating laterally from the stem base and erecting at some distance (10 to 20 mm) from it.