Duplex Retina in the Mesopelagic Deep‐Sea Teleost Lestidiops affinis (Ege, 1930)

Abstract

AbstractThe eye of the deep‐sea teleost Lestidiops affinis has been examined primarily by light microscopy and found to possess a duplex retina consisting of two main divisions, a pure‐cone and a pure‐rod region, with a narrow zone of transition, possessing both cones and rods, joining the two. The pure‐cone region is located in the temporal (caudal) part of the retina subserving binocular vision in the rostral direction. It has an area temporalis retinae with particularly long and densely packed single cones arranged in a regular hexagonal mosaic. Joined (double or twin) cones have not been recognized with certainty in the pure‐cone region. The pure‐rod region, comprising the larger part of the retina, contains rods grouped in bundles separated by retinal pigment epithelium (RPE) processes with pigmented cores. The synaptic endings of the rods are arranged in separate clusters in the outer plexiform layer, there being apparently a separate rod pedicle cluster beneath (vitread to) each rod bundle. Structural comparisons with certain other deep‐sea teleosts suggest the likely presence of a retinal tapetum in L. affinis, i.e. each single cone or rod bundle is situated in a reflecting pit formed by the RPE, with a discrete reflector apposed to the tip of each cone outer segment and the tips of the outer segments of each square‐cut rod bundle.