Marshallia tortuosa
Roemer 1864
Marshallia tortuosa is rare at Misburg and Höver. The specimens shown here are from the Lower Campanian of Höver.
Marshallia tortuosa has a very characteristic twisted habit, resulting from a spiralling arrangement of longitudinal folds in the thin-walled funnel. The individuals can look quite different, depending on the number of folds, which can be between two and at least five. The specimen in the left-hand picture has four folds. None of the examples known to the author show accessory oscula on the fold crests.
Marshallia tortuosa has very conspicuous thin (3 mm), long (50+ mm), hollow roots, which are derived from the dermal cortex and are thus different from the roots of most other sponges.
An example of Marshallia tortuosa with three folds.
The thin appendices on the left and right margin are imperfect roots, whereas the thicker, rounded objects in the middle are overgrowths by Porosphaera sp.
The third example of Marshallia tortuosa consists of five folds; it shows the typical spiralling folds from below. Stem and upper parts are missing.
The lower image shows some details. Notice the very regular dictyonal skeleton exposed in the lower right part. Most of the remainder of the sponge surface is made up of a dermal skeletal modification, where the lychnisk arms are mantled by additional silica, leaving only small, more or less round pores in between.
Marshallia sp.
? new species
There is a second kind of Marshallia present at Höver, which differs from Marshallia tortuosa by having intercalated secondary folds in higher sections of the funnel, having many accessory oscula on the fold crests, and probably by having a proper stem with "normal" roots. (The basal part is missing in all examples of Marshallia tortuosa known to the author, and it is unclear, whether there is a proper stem or not.)
The left-hand picture shows two fragments (tentatively combined from different individuals!), which together may give an impression of the general habit of Marshallia sp..
The second picture is a bottom view of the upper specimen. Notice the round parietal oscula on the outward facing fold crests.
The skeleton of Marshallia sp. is indistinguishable from that of Marshallia tortuosa.