A jellyfish that would not fit in
deutsche Version

Permian yellyfish on laminated chert Usually, accumulated knowledge on fossil and extant species is favourable in the attempt to discover something new on surfaces or cut faces of fossiliferous cherts. The present case is different as the unique object that looks like a polyp near the circular jellyfish imprint has been spotted with a mere curious look at the sample (Fig.1) but people with expert knowledge of jellyfish did not find it even though they had been told it was there. This makes it all the more interesting.

Fig.1: Fracture face of laminated chert of limnic origin, probably Lower Permian, from the Nobitz gravel pit, Saxony, apparently with polyp and medusa stages of jellyfish.
Width of the image 6cm.

Compressed medusae of similar size have been found in similar sediments several times before.
Limnic medusae preserved as imprints in fine-grained Permian sediments in Europe are usually regarded as freshwater hydromedusae of the species Medusina limnica [1].
It may be mentioned here that jellyfish are subdivided into Hydrozoa, Cubozoa, and Scyphozoa, and that their life cycle usually comprises polyp and medusa stages. The way of transition from polyp to medusa is a distinctive feature of the clades. With the polyp stage missing in the hitherto available samples, Medusina has been assigned to the Hydrozoa. The polyp in the present sample is faintly seen upside down near the lower edge of Fig.1, enlarged and upright in Fig.2,
Permian jellyfish polyp
permian jellyfish polyp drawing

Fig.2 (left): Detail of Fig.1  suggesting an interpretation as a polyp prepared to shed its top which is to become a medusa.
Height of the polyp 11mm.

This polyp with its apparent abscission layer of special cells, seen as a thin horizontal line in Fig.2, allows the fossil to be assigned to one of the jellyfish clades. Cubozoan polyps turn into their medusa as a whole, which would not be compatible with Fig.2. Hydrozoan polyps produce medusae by budding, which would not fit either. Only Scyphozoan polyps form abscission layers facilitating the consecutive release of top regions which turn into medusae. Hence, one is tempted to declare the present medusa with polyp a Scyphozoan. However, all extant Scyphozoans are sea jellyfish but this fossil one is silicified in peat-like sediment with terrestrial plant fragments, including parts of parallel-veined leaves of trees. The difficulty could possibly be overcome with the assumption that it was a salt water lake where the marine species had lived and the terrestrial plant litter had got washed into.
The dissolved silica for chert formation had probably been provided by the wide-spread volcanism in Saxony in the Lower Rotliegend [3].

If the present fossil is really a scyphomedusa, it is the first one found in a terrestrial environment. Considering that salt water lakes had been around in Saxony in those times [4], this could well be the case. The interpretation of this fossil as a Scyphozoan raises the question whether or not some or all of the fossil medusae called Medusina and interpreted as Hydrozoans are really Scyphozoans. (It is worth mentioning that the term "hydromedusa" in connection with Medusina is avoided in [2] ).
This roughly 4-sided fragment of a chert layer, 0.85kg, with glossy black side faces as often seen on cherts from Nobitz, had been collected in 2007 by Sieglinde Weiss for its pale circular spots. (For another unique find from the Nobitz gravel pit see Fossil Wood News 10.) Closer inspection in 2008 revealed the thin abscission line in Fig.2 which meant the discovery of the polyp. Since an abscission line would not fit into the established concept of Permian hydromedusae, palaeontologists proposed that the line might be a mere crack. This is contradicted by the observation that a (hardly visible) crack approaches the abscission line on the right and does not run along but proceeds as if the line were not there. Hence, there is no indication that the thin line across the polyp might be a former crack.
It is recommended to closely inspect all samples with alleged hydromedusae in order to possibly spot more of the elusive polyps.     

H.-J. Weiss     2017

[1]  D. Schüppel: Abdrücke von Hydromedusen aus dem Unterrotliegenden des Erzgebirgischen Beckens, Freiberger Forschungshefte C395 (1984), 38-46.
[2]  H. Kozur: die Verbreitung der limnischen Meduse Medusina limnica Müller 1978 im Rotliegenden Mitteleuropas. Paläontolog. Z. 58(1984), 41-50.
[3]  H. Walter: Das Rotliegend der Nordwestsächsischen Senke. Veröff. Naturkundemuseum Chemnitz 29(2006), 157-176.
[4]  J. Schneider, U. Gebhardt: Dasycladaceen und andere "marine" Algen in lacustrischen Kalken des Unter-Perm (Assel) im intermontanen Döhlen-Becken.
        Freiberger Forschungshefte C445 (1992), 66-88.
Scolecopteris pinnule cross-section, Sardinia Permian Chert News16

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