NICKEL, M; Stuttgart University, Germany: Long-term rhythm and functional morphology of contraction in two sponge species of the genus Tethya (Porifera, Hadromerida)

The long-term contraction rhythm of T. wilhelma was investigated by digital time-lapse photography over a period of 8 days. Photographs where taken every 200 seconds. In total 3,185 photographs have been analyzed statistically using the image analysis tool imageJ. No diurnal rhythm of contraction was observed. The sponge contracted regularly for 50-70 minutes every 200 to 300 minutes. Contraction is used by the sponge to exchange a large amount of water in a short time. In addition the sponge reacts on environmental stress by contraction and is able to disburden itself from sediment coverage by contraction. The functional morphology of contraction is described. High resolution 3D-data of the skeleton of T. minuta, obtained by synchrotron micro computed tomography (�CT), was combined with immunohistological and experimental data from T. minuta and T. wilhelma. The contraction is mediated by contractile cells (actinocytes) located in the lacunar cortex of the sponge. Forces are mediated by the mineral as well as the organic, collagenous skeleton of Tethya. A defined inner collagen rich sphere of asters protects the choanoderm against contraction forces. An outer layer of tylasters helps to spread the contraction forces over the sponge surface. In addition it acts as a protective layer against mechanical environmental forces, like sediment or feeding organisms (amphipods, polychaets, snals, etc.). Cellular dynamics during contraction are addressed by digital 4D-epifluorescent- and time-lapse DIC-microscopy. The cellular mode of contraction is discussed as well as the possibility of integration and the triggering mechanism.