Propagation of bioluminescence in Euphysa japonica hydromedusae, (Tubulariidae)

The jellyfish Euphysa emits light when touched, stimulated electrically or shaken in the water. Light is emitted over the whole subumbrellar surface. The source of light is the subumbrellar endodermal epithelium. The response accompanies muscular involution (‘crumpling’) and is spread by all-or-none action potentials propagated in the epithelium itself. Light emission is calcium dependent, but propagation of the triggering events is not. Octanol blocks propagation but light is still emitted in the immediate vicinity of the stimulating electrode. Light emission consists of discrete flashes which sum and facilitate with repeated stimulation. Although the triggering impulses propagate over the entire epithelium, the threshold for light emission varies regionally. The response more closely resembles that described for thesiphonophore Hippopodius than those of leptomedusae such as Aequorea. Light emission is best viewed as a startle response.