Electrical responses of Stomotoca atra induced by an extract of Aequorea aequorea

Abstract

HYDROMEDUSAE swim by rhythmically contracting the circular swimming muscles located in the subumbrella. When species such as Stomotoca atra¹, Sarsia tubulosa^2,3, Proboscidactyla flavicirrata⁴ and Euphysa japonica² are disturbed, either by electrical or mechanical stimulation of the exumbrellar surface, the tentacles contract, swimming stops and a tetanic contraction of the radial muscles causes an infolding of the bell margin (Fig. 1b). This protective response is called crumpling⁵ and is initiated by all-or-nothing potentials in the nerve-free, exumbrellar epithelium^1–4. S. atra, a predacious hydromedusa, is atypical in that it crumples both when disturbed and when in the proximity of large numbers of hydromedusae of several other species. The latter response is initiated by a stimulating substance stored in the mesogloea of the other medusae⁶. The substance is found in crude extracts of Aequorea aequorea, Halistaura cellularia, Phialidium gregarium and S. tubulosa, but not in S. atra itself. The crumpling response induced by the extract has been suggested to be a feeding response, trapping prey in the infolded margin⁶. By recording the electrical activity during the crumpling response initiated by extracts of A. aequorea I have found that this response is coordinated differently from crumpling initiated by electrical or mechanical stimulation.