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Hyalonema sp.

 Faktiske data om fund 
Katalognummer:
625
Accessionsnummer:
DK 678
Samling:
Danekræsamlingen
Samler:
Statens Naturhistorisk Museum
Finder:
Bestemt af:
Arne Thorshøj Nielsen
Lokalitet:
Arnager Pynt
Stratigrafi:
Periode:
Ø. Kridt [Coniacien]
Type:
Konkretion
Sediment:
Arnager Kalk

Billede

Foto ©: Sten Lennart Jakobsen


 Beskrivelse:   af  Arne Thorshøj Nielsen 
Fossile dyriske svampe er særdeles almindelige i Arnager Kalken på Bornholm og en del arter af kiselsvampe er blevet beskrevet. På dansk kaldes disse primitive dyr også for glassvampe. Gruppen lever stadig i bedste velgående i havene. Der er tale om meget primitive dyr, som lever (/levede) af at filtrere havvandet for fødepartikler. Dyriske svampe har ingen indre organer eller mund eller tarmsystem og kan nærmest kaldes en koloni af encellede organismer.

DK 678 adskiller sig fra tidligere fund ved at tilhøre svampe-familien Hyalonematida (underklassen Amphidiscophora), der ekstremt sjældent bevares fossilt. Ind til videre er kun et eneste fossil (slægten Hyalonema) beskrevet fra Øvre Kridt i Tyskland. DK 678 er forholdsvis stor og komplet inkl. rod. De foreløbige undersøgelser viser, at eksemplaret repræsenterer en ny, indtil videre ikke beskrevet art. Dertil kommer, at der måske er tale om en overgangsform - det eneste kendte eksemplar - mellem de 2 slægter Hyalonema og Monorhaphis. Disse slægter er karakteriseret af en forskellig udformning af roden.

Udover at være videnskabeligt interessant er DK 678 velegnet til udstilling.

Udtalelse af PD DR. Dorte Janussen:
In the Upper Cretaceous (Coniacian) Arnager Limestone, fossil sponges preserved as body imprints with pyritized skeletal elements (spicules) are very common. This locality is unique in terms of preservation state and diversity of non-rigid glass sponges, Hexactinellida (Brückner & Janussen 2005, Brückner 2006). However, the new fossil sponge specimen collected at the beach of Arnager Pynt, which was kindly sent to me by Dr. Arne Thorshoej for study and publication, is unique in several respects. First of all, it belongs to the hexactinellid sub-class Amphidiscophora, family Hyalonematidae, which is extremely rare in the fossil record. So far, only one body fossil of the genus Hyalonema has been described, from the upper Campanian of the Münsterland Basin, Germany (Mehl & Hauschke 1995). The present sponge is a comparably large, complete bodily preserved specimen of Hyalonema, including almost the entire root-tuft, and it is very spectacular. According to my observations of this fossil, it is definitely a hyalonematid species new to science and will be described as such in the near future (Janussen in prep.). Furthermore, it may represent a unique transition between the genera Hyalonema and Monorhaphis. The first genus characterized is by slender, mostly twisted root tufts of long, relatively thin anchoring spicules, whereas representatives of the latter are characterized by one single, long thick (up to 1 mm diameter), anchoring needle fixing the sponge in the sediment (e. g. Tabachnick 2002). The present fossil is characterized by a comparably wide root tuft of diverging spicules, a few of which show a remarkable diameter of up to 5 mm. This sponge fossil therefore may represent the so far only known transitional form between the two closely related genera.

Because of its very high scientific value as well as the exceptional beautiful preservation (very suited for public exhibitions), I definitely recommend that this fossil becomes distinguished by the status as Danekrae!

Literature cited:
Brückner, A. (2006): Taxonomy and paleoecology of lyssacinosan Hexactinellida from the Upper Cretaceous (Coniacian) of Bornholm, Denmark, in comparison with other Postpaleozoic representatives.- Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft, 564: 1-103.
Brückner, A. & Janussen, D. 2005: The first entirely preserved fossil sponge species of the genus Rossella (Hexactinellida) from the Upper Cretaceous of Bornholm, Denmark. – Journal of Paleontology, 79 (1): 21-28.
Mehl, D. & Hauschke, N. 1995: Hyalonema cretacea n. sp., first bodily preserved Amphidiscophora (Porifera, Hexactinellida) from the Mesozoic.- Geol. Paläont. Westf., 38: 89-97.
Tabachnick, K. R. (2002) Monorhaophiditae.- In: Hooper, J.N.A. & Van Soest, R.M, Systema Porifera, Kluver Academics/Plenum publ.: 1264-1266.

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