Rapid contractions and associated potentials in a sand-dwelling anemone.

The behaviour of sea anemones ranges from simple reflex activities which are complete within seconds to slow complex movements which last for several hours (Pantin, 1935a; Batham & Pantin, 1950; Robson, 19616; Ross & Sutton, 1961). While the latter are difficult to analyse, the withdrawal or protective responses are very rapid, can be consistently evoked by appropriate electrical stimuli, and have been the most thoroughly studied of all the components of anemone behaviour. These responses are considered to result from the widespread activation of one or more groups of muscles by a through-conduction system, so that there is a sudden closing of the oral disk and symmetrical contraction of the column. Until a short time ago analyses of the properties of the through-conduction system were dependent upon the nature of the evoked mechanical responses. Recently, however, Josephson (1966), using flexible suction electrodes, was able to record muscle action potentials for the first time from Calliactis. These potentials precede rapid contractions of the sphincter muscle by 12 msec, and their size is closely related to the size of the contraction. In the present study the same technique has been employed in an analysis of neuromuscular transmission in a sand-dwelling anemone. This animal, Calamactis, differs from Calliactis in that it lacks a sphincter, and the major effectors are the well developed retractor muscles. The latter have the same general properties as the sphincter, but show distinct differences associated with their greater length and their longitudinal arrangement in this very elongate, burrowing anemone.