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Rhopalia are integrated parts of the central nervous system in box jellyfish


In cubomedusae, the central nervous system (CNS) is found both in the bell (the ring nerve) and in the four eye-bearing sensory structures (the rhopalia). The ring nerve and the rhopalia are connected via the rhopalial stalks and examination of the structure of the rhopalial stalks therefore becomes important when trying to comprehend visual processing. In the present study, the rhopalial stalk of the cubomedusae Tripedalia cystophora has been examined by light microscopy, transmission electron microscopy, and electrophysiology. A major part of the ring nerve is shown to continue into the stalk and to contact the rhopalial neuropil directly. Ultrastructural analysis of synapse distribution in the rhopalial stalk has failed to show any clustering, which indicates that integration of the visual input is probably spread throughout the CNS. Together, the results indicate that cubomedusae have one coherent CNS including the rhopalia. Additionally, a novel gastrodermal nerve has been found in the stalk; this nerve is not involved in visual processing but is likely to be mechanosensory and part of a proprioceptory system.

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We greatly appreciate the excellent laboratory work performed by Rita Wallén and Carina Rasmussen. We also thank the staff at the marine station Isla Magueyes, especially Wilson Rovira, for the help that they provided. Fruitful discussions with Mattias Ekerholm, Lund University, are gratefully acknowledged.

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Correspondence to A. Garm.

Additional information

This work was supported by grants 621-2002-4873 from the Swedish Research Council to D.-E. Nilsson and 21-2204-04 from the Danish Research Council to A. Garm.

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Garm, A., Ekström, P., Boudes, M. et al. Rhopalia are integrated parts of the central nervous system in box jellyfish. Cell Tissue Res 325, 333–343 (2006).

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  • Rhopalia
  • Eyes
  • CNS
  • Synapse
  • Tripedalia cystophora, jellyfish (Cnidaria: Cubozoa)