Endogenous tidal rhythmicity in the littoral pycnogonid Nymphon gracile (Leach)

Abstract

The pycnogonid Nymphon gracile (Leach) has been shown to have an endogenous activity rhythm of tidal frequency, the peak of activity occurring at, or just after, expected high water. Animals collected littorally show some rhythmicity at all times of the year. The rhythm drifts in most individuals when recorded in the laboratory at 20°C, but some animals collected in winter and recorded at 9°C, did not show any drift.