Abstract
Under the action of appropiate releasing stimuli the amphipid, Talitrus saltator, is capable of orienting by the position of the moon in a relatively constant azimuth. This ability functions for 10 or more hours of captivity in constant darkness. Direction of escape and degree of scatter are not noticeably influenced by repeated photo-bulb flashes. Additional evidence supports the hypothesis that the lunar orientation of Talitrus is based upon a continuously operating lunar physiological rhythm. The hypothesis of a single cycle night-time orientation rhythm, advanced for Orchestidea corniculata, does not seem applicable to Talitrus saltator.