The sea anemone Stomphia coccinea, when touched by certain starfishes, frees itself from the substratum, and by a series of waving motions propels itself through the water. This locomotion has been studied by means of direct observation and by analysis of time-lapse, and normal-speed motion-picture films.
Ecological observations and stimulation tests made in the natural environment of the anemone are described and discussed. The musculature of the anemone is described, and the function of the various. muscles is discussed with regard to their participation in swisnming. The muscles that play the most important part in the animal's movement through the water are the parieto-basilar and the circular muscle-sheet. The other muscles are involved in the overall reaction, but act only as aids in maintenance of the form of the anemone during actual swimming.
Experiments involving the ability of several species of starfish to elicit awimsning arc described. It has been established that, of those asteroids tested, only Dermasterias imbricata and Hippasteria spinosa are consistently effective in causing Stomphia to swim.
The possibility that swimming serves as a means of escape from starfish predators is considered. Observations and simple experiments indicate that predation may not be a factor in this relationship between starfishes and the anemone.
Observations of the anemones in their natural environment suggested that swimming might be a means to remove debris settling on the oral disk and eventually burying the animal. Experimentally, this could not be substantiated; silt is removed by the cilia of the oral end of the anemone.
That the starfish release some chemical which serves as a stimulant to the anemone is considered; but experiments indicate that if such a substance is present it probably is not water-soluble.
It was discovered that swimming could be brought about by electrical stimulation. The response is facilitated and can be controlled, to a certain degree, by giving stimuli of proper intensity and frequency for varying periods of time (e.g. 6 volts at 1-sec intervals over a period of z to 8 sec).
Possible uses for the swimming reaction in nature are considered, but this question still remains open to further speculation and experimentation.