AbstractsBiology & Animal Science

Recent stalked crinoids live primarily in the deep sea. First representatives are known from the Ordovician, and were very abundant during several time intervals of the Palaeozoic and Mesozoic era. Living crinoids are passive suspension feeders and typically arrange their body in the so-called parabolic filtration fan, where the arms are bent backwards into the incoming flow. The fossil record provides representatives that differ significantly in their morphology from that of the living forms and were very abundant in shallow water habitats. For those crinoids, different feeding positions have to be assumed. In the presented study, physical models of the recent Hyocrinus sp. and the fossil Encrinus liliiformis were studied in a recirculating flow tank using Particle Image Velocimetry (PIV) to investigate the flow patterns forming around the crowns. In addition, 3D models of the crinoids were analysed with computer simulations applying Computational Fluid Dynamics (CFD). PIV and CFD results were validated against each other, and CFD was then used to investigate additional models including the more complex recent crinoid Neocrinus decorus, a submodel of part of an arm with several pinnules and tube feet, as well as different flow conditions and feeding positions of E. liliiformis. Results for the recent crinoids adopting the parabolic filtration fan showed straight flow of the water through the arms and pinnules. The crown induces a baffling effect such that nutritive particles are slowed down and can be caught by the extended tube feet. The submodel including the finer morphological structures leads to the development of local, small scale recirculation behind the tube feet, but almost no particles are transported back to the oral surface in this current. For the fossil crinoid E. liliiformis, which was probably not able to bend its arms to such an extant as living crinoids, both PIV and CFD results supported a different filtering position, where the crown forms a tearshape. With an aboral inflow and velocities of more than 0.01 m/s, this feeding position results in a recirculation of water into the crown. Particle tracking simulations showed that nutritive particles are then transported onto the oral surface. An opening of the arms increases the strength of the recirculation current, whereas the absence of parts of three arms decreases the recirculation considerably. Inflow from the lateral as well as oral side enables direct catchment of plankton out of the water. The postulated feeding position of E. liliiformis thus worked effectively under varying flow conditions that typically occurred in the shallow water habitats of the Middle Triassic Muschelkalk, which this crinoid inhabited.; Gestielte Crinoiden leben heute, bis auf wenige Ausnahmen, nur noch in der Tiefsee. Sie weisen einen weit zurückreichenden Fossilbericht auf, mit den ersten sicheren Vertretern im Ordovizium. Während des Paläozoikums und Mesozoikums waren sie zeitweise sehr weit verbreitet und besiedelten ausgedehnte Areale in Flachwasserbereichen.…