Abstract
The hawk‐wing conch, Strombus raninus, possesses extremely well developed camera‐type (simple) eyes. Light and electron microscopy were used to generate an accurate scale model of the eye, which was then used for predictions of its optical performance. The eye‐bulb measures approximately 1.6 × 1.9 mm and features a spherical lens, a large vitreous body, and a retina. The lens has a diameter of 950 μm and its centre consists of a seemingly homogeneous core with an approximate radius of 215 μm. The image produced by the lens is apparently aberration‐free and has a short focal length (950 μm). The ratio of the focal length to lens radius is approximately 2, and thus lower than the “Matthiessen ratio” of 2.5 frequently found in aplantic lenses of many marine animals. The crisp images produced by the lens imply the presence of a refractive index gradient despite an apparently homogeneous core. In the central retina, the inter‐receptor angle is 0.47° and the rhabdom diameter is 7.8 μm (5.7 times wider than the diffraction blur circle), indicating a retinal array coarser than that necessary to sample all the information contained in the image. The large aperture (850 μm) means that rays have the opportunity of striking the retina with incident angles of up to 41°, possibly degrading resolution further due to spread of light between rhabdoms (which lack shielding). Different aspects of the eye structure are discussed. © 1994 Wiley‐Liss, Inc.