THE RESPONSES OF THE EPISTELLAR PHOTORECEPTORS TO LIGHT AND THEIR EFFECT ON CIRCADIAN-RHYTHMS IN THE LESSER OCTOPUS, ELEDONE-CIRRHOSA

Extracellular recordings of the light generated receptor potential in the epistellar bodies of the octopus Eledone cirrhosa have shown that these extraocular photoreceptors can respond to light levels lower tha n 0.1 mu W/cm(2) and linearly increase their response with the log of the intensity of illumination. Although the overlying mantle sac wall only permits about 1% of the ambient light to penetrate to the photore ceptors, this is still sufficient for the receptors to be activated at the animal's normal operating depth. Removal of only the epistellar b odies did not prevent the appearance of the normal nocturnal activity pattern of these animals. We therefore conclude that, although the oct opus epistellar bodies could be involved in light generated activity p atterns, they are not essential.