Information Feedback from Photophores and Ventral Countershading

The arrangement of photosensitive vesicles and photophores in two species of mid-water squid suggests that the vesicles function in detecting the intensity of downward-directed surface light and the intensity of light from their own photophores. This information is precisely what is required for an animal to eliminate its ventral shadow by the production of a ventral bioluminescent glow. This arrangement, therefore, offers strong support for the theory of ventral countershading in mid-water animals. CEPHALOPODS have photoreceptive structures other than the eyes. In octopods these organs have been called epistellar bodies (Young, 1929); in squid and cuttlefish they have been labeled the parolfactory vesicles (Boycott and Young, 1956). In both instances the names are associated with the location of the organs: in octopods, on the stellate ganglia; and in squid and cuttlefish, near the olfactory lobe on the optic stalk of the brain. In spite of the different locations of these organs, they are probably homologous structures (Nishioka, Hagadorn, and Bern, 1962; Nishioka et aI., 1966, and personal observations). It is, therefore, no longer desirable to maintain a separate terminology in the different groups. Since neither of the present names is appropriate to all cephalopod groups, it becomes necessary to rename the organs. Since these organs are photoreceptors (Nishioka et aI., 1966; Mauro and Baumann, 1968; Mauro and Sten-Knudsen, 1972), it is suggested that the epistellar bodies and the parolfactoryvesicles be called the photosensitive vesicles.3 I. This work was supported by grant GB 20993 from the National Science Foundation. Manuscript received 10 May 1972. 2 Department ofOceanography, University ofHawaii, Honolulu, Hawaii 96822. 3 An abstract, treating the modifications of the photosensitive vesicles in mid-water squid, was published in the Proceedings of the Joint Oceanographic Assembly, Tokyo, 1971. In this abstract I used the term "photic vesicles." J. Z. Young has since informed me that this term had already been used for certain light-sensitive structures in gastropods. Following his suggestion, I now adopt the term "photosensitive vesicles." 1 The function of the photosensitive vesicles beyond their photosensitive capacity is unknown. One probable function, however, has recently emerged during the course of a study which is attempting to correlate modifications of the photosensitive vesicles with certain aspects of the ecology of mid-water cephalopods off Hawaii. I would like to thank J. Z. Young, University College London; N. B. Marshall, British Museum (Natural History); C. F. E. Roper, Smithsonian Institution; J. M. Arnold, Pacific Biomedical Research Center; T. Okutani, Tokai Regional Fisheries Research Laboratory; and J. Walters and S. Amesbury, University of Hawaii, for reading and commenting on the manuscript. I also thank T. Clarke, University of Hawaii, for providing some of the specimens