Reference: Biol. Bull., 153: 180-197. (August, 1977) LOCOMOTION AND PROPAGATED SKIN IMPULSES IN SALPS (TUNICATA: THALIACEA) G. O. MACK1E AND Q. BONE Biolo,f/y Department, University of Victoria, Victoria, British Columbia, Canada; and The Marine Laboratory, Citadel Hill, Plymouth, England, U.K. With the notable exception of the work of M. Fedele, whose major papers on salps in the period 1923-1933 are cited below, few serious attempts have been made to analyze the behavior of salps. Yet, being large transparent animals with clearly visible and well-defined muscle bands and nerves, with compact brains and interesting behavior, they and the doliolids are potentially the most promising of the tunicates for neurophysiological investigations. Because of their scarcity in most coastal regions, salps have been little studied. The present report is the first electrophysiological investigation of salp behavior and is correspondingly incom-plete or tentative in many respects. The mechanism of locomotion has been studied using techniques similar to those adopted in previous studies of tunicate behavior. These include investigations of the locomotory control mechanisms in the larvacean Oikoplcura ( P>one and Mackie, 1975) and in the tadpole larva of an ascidian, Dcndrodoa (Mackie and Bone, 1976). In both these cases, and now in salps, evidence has been obtained for the existence of "neuroid" conducting epithelia (Mackie, 1970) and for their role as sensory pathways in responses involving changes in locomotory activity. MATERIALS AND METHODS The salps used in this study were caught in plankton nets or scooped from the water in glass bottles in the bay of Villefranche-sur-Mer, France, during the period December 1973 to March 1974. They were kept in circulating seawater aquaria at the Station Zoologique and were used for experiments soon after capture. Taxonomic and biological accounts of the species used ( Thalia democratica, Sal pa jiisifunnis, Sal pa ina.viina, Ihlca punctata, and Pcgca confoedcrata) are given by Branconnot (1973). Ihle (1933, 1958) provides indispensible back-ground information on salp morphology and relationships. Formalin-fixed and fresh tissues were examined by Nomarski and phase con-trast microscopy. Material was fixed for electron microscopy in 5% cacodylate-bufferecl glutaraldehyde in sea water, followed by postfixation in \% osmium tetroxide. Sections were stained with uranyl acetate and lead citrate prior to examination with a Philips EM-200. Fine polyethylene suction electrodes were used for recording externally from the muscle bands and conducting epithelia. Signals were amplified and displayed on a Grass Polygraph and simultaneously on a Tektronix storage oscilloscope. A Grass stimulator was used for electrical stimulation. Intracellular recordings were made with glass micropipettes filled with 3 M KC1 having resistances in the range 180
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