ELECTRICAL ACTIVITY AND BEHAVIOR IN THE SOLITARY HYDROID CORYMORPHA PALMA. I. SPONTANEOUS ACTIVITY IN WHOLE ANIMALS AND IN ISOLATED PARTS

¹ Department of Biological Sciences, University of California, Santa Barbara, California 93106

1. There is a clear association between certain aspects of the behavior of Corymorpha palma and electrical activity of five interacting pulse systems located in the stalk, hydranth, proximal tentacles, distal tentacles, and gonophore peduncles.

2. Stalk pulses normally occur in bursts of 10 to 30, and are associated with contraction of the longitudinal musculature of the stalk. They apparently may originate anywhere on the stalk, but are usually initiated in its basal half.

3. Hydranth pulses occur in bursts of varying lengths, the most common consisting of 2-6 pulses. These pulses are associated with a "concert" which varies greatly in intensity from animal to animal. A full concert involves contraction of the proboscis as the proximal tentacles come in around it, though some animals show nothing more than a twitch of the proximal tentacles or a barely perceptible contraction of the proboscis.

4. Proximal and distal tentacle pulses may occur singly or in bursts which are usually triggered from outside the tentacle. While the tentacle is attached to the animal there is sometimes no obvious behavioral correlate of these pulses; but with excised tentacles there is usually a flexion or slight contraction associated with each pulse or burst of pulses.

5. Gonophore peduncle pulses may occur singly or in bursts which are usually triggered from outside the peduncle. In some cases there is no obvious behavioral response to these pulses, while in others there is a contraction of the ectodermal musculature.

6. The pulse systems are arranged in a coupled hierarchy with stalk bursts normally triggering activity everywhere else in the animal, either directly or by way of the hydranth pulse system. This triggering results in concerts associated with stalk contraction; such concerts occur either irregularly or at fairly regular intervals of several minutes in undisturbed animals. Hydranth pulses trigger pulses in both sets of tentacles, resulting in concerts. Excision experiments were used to clarify these relationships between the various pulse systems.

7. Temperature has a marked effect on pulse activity. Proximal tentacle pulses and hydranth pulses are much more frequent at high temperatures and are less frequent at low temperatures over the range 10-30° C.

8. The spontaneous pulse systems of Tubularia and Corymorpha are similar in many respects.

9. The pulse systems of Corymorpha cannot he differentiated on the basis of pulse duration, amplitude, or waveform.

10. Much of the more complex behavior of Corymorpha cannot be explained in terms of recordable electrical activity. The mechanisms by which this behavior is controlled remain unknown.