Multiple conducting systems in the cubomedusa Carybdea marsupialis

Acute responses to mechanical, electrical, and photic stimuli were used to describe neural conducting systems in the cubomedusan jellyfish Carybdea marsupialis underlying three behaviors: contractile responses of single tentacles, protective crumple responses, and alterations of swimming activity by the visual system. Responses of single tentacles consisted of tentacular shortening and inward pedalial bending, and were accompanied by bursts of extracellularly recorded spike activity that were restricted to the stimulated tentacle. With nociceptive stimuli delivered to the subumbrella or margin, all four tentacles produced similar responses in a crumple response. The spike bursts in all four tentacles showed coordinated firing as long as the nerve ring was intact. Crumples were still produced following cuts through the nerve ring, but the activity in individual tentacles was no longer coordinated. Responses to light-on stimulation of a rhopalium, as recorded from the pacemaker region, were weak and inconsistent, but when present, resulted in a stimulation of swimming activity. In comparison, light-off responses were robust and resulted in temporary inhibition of swimming activity. Light-off responses were conducted in the nerve ring to unstimulated rhopalia. In conclusion, three conducting systems have been described as components of the rhopalia-nerve ring centralized system in Carybdea: the swim motor system, the crumple coordination system, and the light-off response system.