Diurnal periodicity of the squirting of Holocynthia roretzi

In order to make clear the physiological ecology of squirting exhibited by Halocynthia roretzi, we examined the periodicity of squirting and the factor on the periodicity through the experiment measuring the internal pressure. On the natural condition, the small squirting showed an obvious periodicity of 24 hours cycle, and the large one displayed a weak periodicity for one of four specimens. However, ascidians had no rhythms of squirting in the dark. On 8L8D condition, we found a periodicity of approximately 16 h in small squirting. These results suggest that the periodicity of squirting does not depend on the biological clock, but attributes to increase of the small squirting due to their responses for the light.