Postnatal persistence of episodic spontaneous rapid-body-movement bursts and twitches in the cuttlefish, Sepia officinalis

Measurements made under microscopic examination of spontaneous motility shortly before and after hatching in the cuttlefish, Sepia officinalis, revealed a developmental continuity wherein bursts of vigorous mantle contractions lasting a few seconds at most, often associated with irregular twitching of the tentacles and head (but less often of the eyes or chromatophores), follow each other at variable intervals ranging from less than 5 s to many minutes. Releasing the animals prematurely into sea water had no qualitative effect on visible movements but augmented their incidence considerably if done several days before hatching, while reducing it if done shortly prior to hatching. That this was not an age effect is suggested by the lack of any difference between the two groups after their emergence from the egg capsule. The temporal patterning of these stereotyped ‘rapid-body-movements’, defined here as an immature subclass of ‘motorically active sleep’, differed both quantitatively and qualitatively from the repetitive bouts of swimming (‘active wakefulness’) that also occur episodically in hatchlings but not in embryos. Similar to endothermic vertebrates, sleep bursts in cuttlefish rapidly became much less frequent with increasing age as the incidence of wake-like behaviour increased. Spontaneous embryonic motility, c.q., active sleep, thus appears to constitute an ontogenetically and phylogenetically primordial behavioural state which continues without discontinuity into postnatal life, with classical ‘rapid-eye-movement’, c.q., ‘paradoxical’ sleep, being a later appearing special case.