Neuromuscular Activity in the Swimming Sea Anemone, Stomphja

The spontaneous activity and responses to electric stimulation of actinians have been intensively studied (e.g. Pantin, 1935a, b, c, d; Ross, 1952, 1957a, b; Horridge, 1958) for the light which they might throw on the functioning of the 'elementary nervous system', i.e. a nervous network lacking the physical concentration of neurones found in ganglia and brains. It seems desirable to add to this knowledge data from the swimming sea anemone Stomphia coccinea. This animal, although not yet well known, is evidently widely distributed, having been recorded from Millport, in the Clyde, Scotland (Stephenson, 1935), and from President Channel, Puget Sound, Washington, U.S.A. (Yentsch & Pierce, 1955). It should be pointed out, however, that the species identity of animals from the two regions has yet to be established with certainty. Stephenson (1935) noted that Stomphia is capable of becoming curiously active (for a sea anemone) twitching its 'tail' and 'jumping'. Similar activities can be elicited from the Puget Sound specimens by two species of starfish from the same region (although not the same habitat), Dermasterias imbricata and Hippasteria spirosa (Yentsch & Pierce, 1955; Sund, 1958). Details of the swimming activity have been described by Sund (1958). Since the species reacts to the starfish named, by giving a set of distinct reactions which are usually executed in the same sequence, it can be said to show a high level of integrated activity, possibly higher than any known in other actinians. The following distinct parts of the response can usually be observed, in the following sequence. The division and resulting emphasis is based on my own observations, but closely follows Sund's description: