a1 School of Animal Biology, University College of North Wales, Bangor, Gwynedd LL57 2UW
In recent years several workers have postulated the occurrence in a number of coastal animals of endogenous behaviour and physiological rhythms of semilunar periodicity (see Naylor, 1982). However, only a few of these long term rhythms have been demonstrated as free-running cyclical behaviour over long periods of time in constant conditions. For example, the supra-littoral amphipod Talitrus saltator (Montagu) has been shown to express semilunar variations in daily locomotor activity over three cycles of neap/spring tides during 46 days in constant conditions in the laboratory (Williams, 1979). In contrast, in the mid-shore sand-beach isopod E. pulchra (Leach) semilunar variations in swimming behaviour (Fish & Fish, 1972; Alheit & Naylor, 1976) and of respiration (Hastings, 1981a) have so far been demonstrated only in isopods collected at various stages of the neaps/springs cycle of tides and recorded for a few days in the laboratory. It, therefore, still remains to confirm unequivocally in Eurydice, and in many other forms, which appear to show semilunar periodicity, that such rhythmicity is expressed as a free-running rhythm over long periods of time in constant conditions.