The pedal disc of the swimming sea anemone Stomphia coccinea during detachment, swimming, and resettlement

Abstract

The pedal disc was studied during the "swimming" response of Stomphia coccinea by use of photography and visual aids, certain experimental procedures, and histological preparations. At the moment of release, deep ridges and clefts appeared along the lines of the mesenteries, reducing the surface area by about one-half. Circular muscles on the pedal disc and vertically inserted muscles at the bases of the mesenteries were seen. These together would account for the observed pattern. The breaking of the adhesive sole by the furrowing of the surface, the concavity of the pedal disc produced by parietobasilar contractions, and the dissolution of an adhesive substance seemed all to be involved in the detachment of the animal in response to a swimming stimulus. During the resettling of S. coccinea after swimming, the pedal disc became very sticky, especially if the tentacles had touched the shell. This stickiness coincided with a general discharge of nematocysts (microbasic p-mastigophores) from the pedal disc. The active functions of the pedal disc in the release and resettlement of S. coccinea were discussed and it was pointed out that the basal area is by no means a passive element in the behavior patterns of actinians.