Meeting Abstract

9.6  Thursday, Jan. 3  Elastic energy storage in a contracting poriferan? Quantitative imaging of morphological dynamics using synchrotron radiation based x-ray microtomography (SR-�CT) and in vivo-microradiography NICKEL, M; Institut fuer Spezielle Zoologie und Entwicklungsbiologie, FSU Jena, Germany Nickel@porifera.net

The poriferan Tethya wilhelma is a model to investigate early evolved metazoan contractile tissues. The substantial contractions of the sponge affect mainly the canal system and the mesohyle. The endopinacoderm represents the major contractile effector. It is unknown, which role the mesohyle plays in contraction and expansion. Combining SEM and SR-�CT, we visualized and quantified volume and surface changes of the mesohyle and the canals. The lacunae of the incurrent system and the major channels almost completely collapse during contraction, while parts of the mesohyle increase volume, potentially storing elastic energy. Using SR-in vivo-microradiography, we followed the dynamics of the sponge skeletons during initial and stalled contraction phases. The centre of the radial skeleton displayed prominent displacement during initial phase, followed by a re-positioning during stalled phase, supporting an elastic energy component in post-contraction. A bi-phase expansion kinetics points at two combined mechanisms. Elastic energy stored in the mesohyle seems to be one of the components. For the second component alternative hypotheses can be postulated: 1. partial inflation by internal water pressure (hydrodynamic skeleton); 2. contraction of ECM compounds (mutable contractile collagen); 3. contractile cells in the mesohyle (myocytes/actinocytes). Evidence for all alternatives will be presented and the high regulatory complexity within such �simple� metazoans will be addressed.