ABSTRACT
Stalked crinoids are deep sea animals which have rarely been observed as living animals. Recent observations from submersibles and in the aquarium (Messing et al. 1980, Baumiller et al. 1991) showed that stalked crinoids can actively relocate using their arms for crawling and climbing. Analysis of the movement of arms and stalk, however, has never been done. We present the first detailed study based on video observations. We used a camera of high sensitivity and low intensity red light. Additional recordings on a time-lapse recorder allowed long-term (up to 9 hours) observations of overall movements. The animals were kept for several month in aquaria so that repeated observations of their behaviour could be done. We found, that M. rotundus moves rather quickly. We could distinguish three types of movement: crawling, climbing and bending of the stalk. We observed speeds of ca. 50 cm/hour. The animals mainly pulled their body with the leading arms; sometimes the following arms also helped in stemming the animal forward. The animals climbed up a lattice at speeds of up to 5 cm/hour. In this case only the leading arms were active in pulling the animal up. The power-stroke of the leading arms during crawling and climbing was accomplished by aboral bending of the arms. The arm contains no muscles on the aboral side but an elastic ligament (see Birenheide et al., this conference). Thus it seems likely that M. rotundus climbs and crawls using the recoil of an elastic ligament for the power stroke of its arms. In some cases we could document active bending of cirri. The bending mechanism is not clear, however, because the cirri of stalked crinoids are believed to contain no muscles. We also observed flaccid cirri and stiff cirri at the same time in the same animal. We suggest that the connective tissue that connects the ossicles of the cirri is a catch connective tissue, i.e., it can change its mechanical properties under nervous control.
