The role of a ‘local electrical conduction system’ during feeding in the Devonshire cup coralCaryophyllia smithiiStokes and Broderip

Abstract

The electrical conduction systems underlying the control of feeding behaviour are described for the solitary cup coralCaryophyllia smithii. A nerve net and a slow conduction system were found to conduct non-decrementally to all parts of the animal and to control symmetrical parts of the feeding behaviour such as polyp expansion. The slow system was activated by receptors on the tentacles and oral disc. Of particular interest was the presence of a ‘local conduction system’ in the tentacles and oral disc. This system was shown to be important in the control of local, asymmetrical parts of the feeding behaviour such as the movements of single tentacles. The local conduction system consisted of radially conducting units each of which consisted of a single tentacle and its associated sector of oral disc. This allowed the radial spread of excitation (at less than 2 cm s-1) from tentacle to mouth or mouth to tentacle but did not allow excitation to spread around the oral disc. The threshold for excitation of the local conduction system was above that of the nerve net or slow conduction system. The cellular basis for local conduction is unknown but may involve the oral disc radial muscles and the tentacle longitudinal muscles. By appropriate electrical stimulation of the nerve net, slow system and local conduction system, a complete sequence of feeding behaviour could be evoked. This closely resembled the behaviour shown during normal feeding and included polyp expansion, local pharynx movements and local tentacle bending. It is concluded that ‘local conduction’ is an important element to include in models purporting to explain the control of anthozoan behaviour, particularly that in which local movements are important.