Vision in the southern hemisphere lamprey Mordacia mordax: Spatial distribution, spectral absorption characteristics, and optical sensitivity of a single class of retinal photoreceptor

S.P. Collin, N. Hart, K.M. Wallace, Julia Shand, I.C. Potter

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    The dorso-laterally located eyes of the southern hemisphere lamprey Mordacia mordax (Agnatha) contain a single morphological type of retinal photoreceptor, which possesses ultrastructural characteristics of both rods and cones. This photoreceptor has a large refractile ellipsosome in the inner segment and a long cylindrical outer segment surrounded by a retinal pigment epithelium that contains two types of tapetal reflectors. The photoreceptors form a hexagonal array and attain their peak density (33,200 receptors/mm(2)) in the ventro-temporal retina. Using the size and spacing of the photoreceptors and direct measures of aperture size and eye dimensions, the peak Spatial resolving power and optical sensitivity are estimated to be 1.7 cycles deg(-1) (minimum separable angle of 34'7") and 0.64 mum(2) steradian (white light) and 1.38 mum(2) steradian (preferred wavelength or lambda(max)), respectively. Microspectrophotometry reveals that the visual pigment located within the outer segment is a rhodopsin with a wavelength of maximum absorbance (lambda(max)) at 514 nm. The ellipsosome has very low absorptance (
    Original languageEnglish
    Pages (from-to)765-773
    JournalVisual Neuroscience
    Publication statusPublished - 2004


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