Cretaceous sponges from the Campanian of Misburg and Höver
cf. Rhytistamnia longitudinalis
Rhytistamnia longitudinalis was originally described as Cephalites longitudinalis by Toulmin Smith (1848) from the English Chalk, and by Pomel (1872) from Algeria, but it has not been reported from Germany before. Two specimens of a sponge similar to Rhytistamnia longitudinalis were found in the Upper Campanian of the Teutonia quarry in 2009.
The first specimen shown here in top and side view, although incomplete, shows the typical flat marginal surface which terminates the thick (8 mm) funnel wall. It consists of a narrow funnel, which is widening towards the top.
The gastral surface of the specimen bears numerous circular to slightly oval postica, approximately 1.5 mm wide, which are aligned longitudinally near the margin, but arranged more randomly near the funnel bottom. The bridges between the postica are slightly convex and 1.5 to 2 mm wide.
Near the funnel margin, the dermal surface of Rhytistamnia longitudinalis shows narrow (less than 0.5 mm), deeply incised and discontinuous longitudinal furrows which separate broad, flat to convex bridges. Closer to the base, the longitudinal arrangement disappears and becomes more patchy and random, with irregularly shaped pores up to 1 mm wide. The bridges bear numerous tiny ostia of variable diameter, as on the gastral surface.
The dictyonal skeletal framework is quite regular and consists of fused lychnisks. The gastral and dermal surfaces are covered by a dense cortex with a rough appearance, while the margin is made up of a microporous, smooth, shiny surface.
The second specimen shown here in different views is more complete. Its flat margin is 5 mm high and its funnel is quite flat. The stem is scabbard-like (a feature not recognized with the first specimen) and parietal oscula are visible along its narrow edges.
The exhalent pores on the gastral surface are longitudinally aligned and show a vague in quincunx arrangement.
The distribution of ostia (1 mm wide) on the dermal side seems random and the outline of the pores is irregular. At variance to the first specimen of Rhytistamnia longitudinalis, the dermal side does not show any furrows.
The two specimens from Misburg are interesting intermediates between thin-walled Ventriculites-type sponges with simple epirhyses and aporhyses, and thick-walled representatives like Camerospongia fungiformis with labyrinthine canalization (cf. Reid, 2004, p 53). The presence of scabbard-like stems and flat funnels distinguishes the present specimens from Rhytistamnia longitudinalis as described by Toulmin Smith (1848).
last update: 04 August, 2009