An international team of researchers, led by the University of Trieste and the National Institute of Oceanography and Applied Geophysics (OGS), has discovered in the jellyfish Cotylorhiza tuberculata (commonly known as ‘fried egg jellyfish’ or under the improper name ‘Mediterranean Jelly’) an articulated digestive system, similar to that of more sophisticated organisms, revealing a surprisingly complex internal anatomy that revolutionises the idea of jellyfish as ‘simple’ animals.

The results of the study were published in the scientific journal PLOS One.

Partners of the study include Elettra-Sincrotrone Trieste S.C.p.A., the University of Milan, the Slovenian National Building and Civil Engineering Institute of Ljubljana, the University of Primorska and the Aquarium in Piran.

Massimo Avian, associate professor at the Department of Life Sciences of the University of Trieste and Gregorio Motta, post-doc, commented: ‘In order to analyse the anatomical structure of the jellyfish, overcoming the difficulties linked to the fragility and opacity of the tissues, we used a state-of-the-art technique, injecting a resin into the gastrovascular system of the invertebrate which, once hardened, made it possible to obtain a perfect, three-dimensional copy of all the internal channels. The resulting cast was then analysed with an X-ray microtomography”.

The technique used by the researchers made it possible to discover real channels that branch off into the oral arms of the jellyfish, each of which has a central bottleneck, which functionally divides it into two semi-channels. Functional anatomy experiments, carried out by injecting non-toxic dyes into the stomach of live jellyfish to observe internal flows, have also shown that in these channels there is a two-way circulation. The seawater, rich in prey, is initially ingested by the innermost openings of the arms. After reaching the stomach cavity through the innermost semi-channel, after digestion, it descends to the second semi-channel (external), and then is expelled from the most peripheral and distal openings of the oral arms, expansions similar to large tentacles that are observed under the umbrella.

Valentina Tirelli, a researcher at the National Institute of Oceanography and Applied Geophysics (OGS) among the authors of the study, states: ‘It has always been thought that in jellyfish the same opening served as both mouth and anus. On the other hand, this study shows that there is also a specialisation in Cotylorhiza tuberculata, with pores dedicated to the entry of food and others to the expulsion of waste products, to form a system that resembles a “through-gut” digestive tract, typical of more evolved animals. A similar system had already been identified by some of the co-authors of this work in another jellyfish, Rhizostoma pulmo. As these two species are phylogenetically distant, we hypothesize that this complex digestive mechanism could be much more prevalent among jellyfish than one might imagine.’

The research allowed to deepen the study of the biology of a common creature in our seas, demonstrating through modern observational techniques that evolution can produce complex solutions independently and unexpectedly, even in organisms often considered erroneously primitive.

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Full study published on PLOS One

New advances in jellyfish anatomy: the benefits of endocasts and X-ray microtomography in the investigation of the gastrovascular system of Cotylorhiza tuberculata (Scyphozoa; Rhizostomeae; Cepheidae)

Gregorio Motta1,2*, Marco Voltolini3, Lucia Mancini4, Diego Dreossi5, Francesco Brun6, Valentina Tirelli7,8, Lorenzo Peter Castelletto1, Manja Rogelja9, Antonio Terlizzi1,8, Massimo Avian1

1. Department of Life Sciences, University of Trieste, Trieste, Italy
2. Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Napoli, Italy
3. Department of Earth Science Ardito Desio, University of Milano, Milano, Italy
4. Slovenian National Building and Civil Engineering Institute, Ljubljana, Slovenia
5. Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Trieste, Italy
6. Department of Engineering and Architecture, University of Trieste, Trieste, Italy
7. National Institute of Oceanography and Applied Geophysics, Trieste, Italy
8. National Biodiversity Future Center (NBFC), National Biodiversity Future Center, Palermo, Italy
9. University of Primorska, Aquarium Piran, Piran, Slovenia