NICKEL, M.*; VITELLO, M.; BR�MMER, F.; Biological Institute of University Stuttgart, Germany: Dynamics of cellular movements in the locomotion of the sponge Tethya wilhelma

The globular sponge Tethya wilhelma SAR�, SAR�, NICKEL & BR�MMER 2001 (Porifera, Demospongiae, Hadromerida, � 5-30 mm) is capable of locomotion. Many sponges display very slow body dislocation, but several small species of the genus Tethya are among the fastest (up to 2 mm�h^-1). The movement is accompanied by the production of long thin body extensions, which are stabilised by bundles of 800-1350 �m long siliceous spicules (strongyloxeas). Elongation and reduction rate can be higher than 5 mm�h^-1. Some body extensions produce buds for asexual reproduction, while most serve to investigate the environment and reach several cm in length. If an extension reaches substrate somewhere it attaches within minutes. If it doesn’t attach anywhere it is reduced. By confocal in vivo laserscanning microscopy and digital time-lapse video-microscopy we investigated the cellular dynamics inside the body extensions. The main cell types are pinacocytes, granulose amoebocytes, multipolar fusiform cells and extremely long (sometimes longer than 200 �m) slender, fusiform actinocytes. The later type is associated with the strongyloxea bundles in the core of the extension. Contraction and active movement of the actinocytes was recorded. We could demostrate that all cell types display active movement. The high cellular dynamic is the driving force of the body dislocation. Movement is directed towards attached extensions which are thickened beforehand by immigrating cells. The question of signalling and integration is addressed with first results on chemical messengers. We present first hypothetical models for cellular sequences involved in the locomotion of T. wilhelma, which may partly be generalised for other sponges.