Co-Ordination of Pedal-Disk Detachment in the Sea Anemone Calliactis Parasitica

Electrical activity has been recorded from the sphincter region of Calliactis parasitica during the behavioural sequence in which the anemone detaches from the substrate and attaches to a Buccinum shell. The ectodermal slow-conduction system (SS1) fires repetitively, the majority of observed pulses occurring in the period prior to detachment (a typical example is 25 SS1 pulses at an average frequency of 1 pulse/ 7 sec.). Shell-tentacle contact is essential for stimulation of SS1 activity. Mechanical stimulation of the column excites the SS1, and 30 stimuli at a frequency of about one shock/5 sec. give pedal disk detachment. Electrical stimulation of the ectoderm excites the SS1 and about 30 stimuli at frequencies between one shock/3 sec. and one shock/9 sec. produce detachment. Detachment and the SS1 have an identical stimulus threshold. It is concluded that detachment is co-ordinated by the SS1.