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Journal of Experimental Biology 50,501-513 (1969)
Published by Company of Biologists 1969

The Responses of Nephtys (Polychaeta: Annelida) to Changes in Hydrostatic Pressure

ELFED MORGAN ¹

¹ Department of Zoology and Comparative Physiology, University of Birmingham

1. An increase in pressure elicited swimming in Nephtys, the number of worms induced to swim being related to the amplitude of the pressure change within the range of stimuli investigated. A decrease in pressure inhibited swimming.

2. The latency of the response to both an increase and a decrease also appears to be related to the magnitude of the stimulus, the worms responding more rapidly to the bigger pressure changes.

3. Brief pulses of pressure lasting 1 sec. elicited neither increase nor decrease in the level of swimming, but pulses of 5 sec. duration induced some individuals to swim. Releasing the pressure at the end of the 5 sec. period resulted in a decrease in the swimming activity below the pre-stimulus level. It is suggested that the different responses may be mediated via separate receptor mechanisms.

4. Phase-angle analysis of the responses to cyclical changes in pressure suggested that the worms were responding primarily to the rate of change of pressure, but the response did not appear to be a simple sine-function of the stimulus. The worms also seemed to be responding in part to some component occurring at twice the basic cycle.