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Journal of Experimental Biology 62,389-404 (1975)
Published by Company of Biologists 1975

Electrophysiology and Co-ordinated Behavioural Responses in the Colonial Bryozoan Membranipora Membranacea (L.)

J. P. THORPE ¹, G. A. B. SHELTON ², and M. S. LAVERACK ²

¹ University College of Swansea, Swansea, U.K.
² Gatty Marine Laboratory and Department of Natural History, University of St Andrews, Scotland

1. There is a colonial retraction response in the Bryozoans Membranipora membranacea and Electra pilosa.

2. The conduction velocity of the response is about 100 cm sec^-1.

3. The colonial response will circumnavigate the end of a cut, but will not cross it.

4. The lophophore retraction time is 60-80 msec.

5. The lophophore retractor muscle with a peak contraction rate of 20 + muscle lengths per second is probably one of the fastest contracting muscles known.

6. The colonial responses to successive stimuli under certain circumstances are similar to those of some corals.

7. Nervous pulses can be recorded travelling across the colony at the same velocity as the colonial response.

8. Increases and decreases in the number and frequency of T₁ pulses correspond with increases and decreases in the area and duration of the colonial response and are produced in response to the same stimuli.

9. Other pulses can be recorded which correspond to the retraction of the lophophore retractor muscle.

10. The lophophore retractor muscle is apparently under the control of a giant axon from the zooidal ganglion.

11. The colonial nervous system has many of the properties expected of a nerve plexus.