Swimming in the sea anemone Stomphia coccinea triggered by a slow conduction system

Abstract

THERE has been great interest in the sea anemone Stomphia coccinea since its remarkable swimming response to the starfish Dermasterias imbricata was first discovered¹. On contact with Dermasterias, this anemone rapidly detaches from the substrate and undergoes a series of swimming movements involving flexions of the column. The starfish Hippasteria spinosa² and a nudibranch, Aeolidia papillosa³ also evoke swimming. Previous attempts to analyse this response physiologically were based on indirect observations of swimming induced by electrical stimulation. There were difficulties in explaining the coordination of the swimming response in terms of a single nerve net and it has been suggested that the swimming response is controlled by a separate system⁴. The electrical activity from sea anemones can be measured and correlated with various behaviour patterns^5,6. Use of these techniques with S. coccinea has shown that a slow conduction system, quite distinct from the familiar through-conducting nerve net⁷ always becomes active when Dermasterias contacts Stomphia. This activity, it seems, triggers the entire swimming sequence.