Rythme d'activité endogène chez un nébaliacé (Crustace phyllocaride)

In constant conditions and continuous darkness, the burrowing species Nebalia bipes (Fabricius) exhibits a clear circadian rhythm of emergence from the substratum and of swimming activity. The rhythm, in which activity occurs during the ‘expected night’, is obvious in both males and females and can remain overt for several weeks.The ‘free-running period’, although variable, is ≈ 24 h 20 min in a calm environment and at 18 °C. During the first day of the experiments, the swimming activity of freshly collected animals increases abruptly at dusk and then decreases gradually towards dawn. It has been possible to change the phase of the rhythm by subjecting the animals to a reversed LD schedule.The synchronization seems to result from the high photonegativity of Nebalia in normal daylight. The results of some experiments carried out with young juvenile animals suggests that the synchronization may possibly take place during the incubation period.