Functional Micromorphology of Sponges (Porifera) M. Nickel, E. Bullinger 1 , H.M. Reiswig 2 , T. Donath 3 and F. Beckmann 3 Department of Zoology, Biological Institute, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany 1 Institute for Systems Theory in Engineering, University of Stuttgart, 70550 Stuttgart, Germany 2 Biology Department, University of Victoria, P.O. Box 3020 Stn. CSC, Victoria V8W 3N5, B.C. Canada 3 GKSS Forschungszentrum, Max-Planck-Str. 1, 21502 Geesthacht, Germany. Sponges (Porifera) are sessile, filter-feeding animals. They live mainly in the sea, but some groups also inhabit freshwater environment. In recent years interest in sponges rose due to their high diversity of secondary metabolites of pharmaceutical value. Therefore, sponges became interesting for pharmacology and biotechno- logy, aiming production of sponge biomass and metabolites. Soon it became evident that a more detailed knowledge on the general biology of sponges is a prerequisite for successful cultivation. Cellular growth and synthesis of skeletal elements are connected in sponges. The skeletons consist of organic substances, like collagen and its derivative spongin, in conjunction with mineral sclera (spicules) in most groups of the phylum Porifera [1, 2]. The main function is to stabilise the bodies of sponges. On the other hand the skeletal elements possess a variety of other functions in contraction and locomotion of sponges. Since these processes are slow and inconspicuous they are not well investigated. Nevertheless, they are very important in the life of sponges, since they are linked to the nutrition (filter feeding activity) and the response to short-term and long-term environmental changes. A wide variety of spicule forms can be found, which reflects their various physical functions. This variety of functions is neither well investigated, nor well understood. Our project aims to understand the functional micromorphology of sponges, by applying synchrotron radiation based micro computed tomography SR-µCT. We performed experiments at HASYLAB beamline BW2 on dead, preserved sponges as well as on living material. In 2004 we mainly focused on two sponge species. Tethya spp. The demosponge sister species T. wilhelma and T. minuta display conspicuous body contractions, which have recently been characterized [3]. The structure of the skeleton of T. minuta has been imaged by SR-µCT and visualized in preliminary experiments in 2002 [4]. Meanwhile we have developed a Matlab-based software tool, to quantitatively analyze the sponge spicules in the 3D-dataset. We were able to automatically detect and measure all 16.900 megaster-type (oxyaster) spicules to create an extensive morphometric dataset, representing the first quantitative analysis of a complete set of a single spicule within a sponge. We were able to show that >98.5 % of all megasters are arranged within a distinct sphere, supporting the filtering core unit during contraction of the outer cortex, by deflecting contraction forces from the sponge core (Nickel, Bullinger & Beckmann, submitted). In 2004, we extended our work on T. wilhelma. Using the same experimental set-up than before [4], we imaged the complete skeletal structures of a contracted and a non-contracted adult specimen and an asexual reproduction body (bud), which was amputated from an adult sponge at an early stage, just several days after Figure 1 A. The skeletal morphology of a T. wilhelma bud, visualised by SR-µCT. msb, macrosclere bundles; pmas, primordial megaster sphere. B – C. 3D-reconstruction of a corrosion cast of a part of the T. wilhelma aquiferous system; osc; osculum region; lac; cortex-lacunae region; chd, choanoderm. A B C msb pmas osc lac chd osc lac chd