THE EYE STRUCTURE OF THE BIOLUMINESCENT FIREWORM OF BERMUDA, ODONTOSYLLIS ENOPLA

¹ Carnegie-Mellon University, Mellon Institute, Department of Biological Sciences, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213
² Magee-Womens Hospital, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania 15260

The polychaete anneid, Odontosyllis enopla Verril of the family syllidae in the Bermudas, possesses a lunar periodicity and bioluminesces during the mating period. Odontosyllis has four eyes arranged so that two are located on each side of its head. The eyes are situated on lobes that have some degree of movement. Light sensitivity is maximum for illumination along the optical axis, which is different for the anterior and posterior pairs. The eye resides in a cavity formed by the pigment granules, and is structured of a lens, photoreceptor cells, the retina, and pigment granules. The retinal photoreceptors approach and surround the lens. The photoreceptors are formed of membranous processes, lamellae, and are similar in structure to the rhabdomeric photoreceptors of arthropods, cephalopod mollusc eyes, and the retinal rod outer segment of vertebrate eyes. The lens is a spheroidal body composed of cells. Closely associated with the lens are rods (tubes) about 60 nm in diameter arranged in linear arrays, suggesting that they are fiber optic bundles. The function of the fiber optic system could be to detect the direction of the bioluminescent light and to maximize the light-collecting ability of the eye.