The photoreceptors of the west indian manatee

Authors

  • Joel L. Cohen,

    1. University of Miami, Rosensteil School of Marine and Atmospheric Sciences, Miami, Florida 33149
    Current affiliation:
    1. Department of Ophthalmology and Physiology, New York University School of Medicine, 550 First Avenue, New York, NY 10016
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  • Dr. Gail S. Tucker,

    Corresponding author
    1. University of Miami School of Medicine, W.L. McKnight Vision Research Center, Miami, Florida 33136
    • University of Miami School of Medicine, W.L. McKnight Vision Research Center, 1638 N.W. 10th Avenue, Miami, FL 33136
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  • Daniel K. Odell

    1. University of Miami, Rosensteil School of Marine and Atmospheric Sciences, Miami, Florida 33149
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Abstract

Using light and electron microscopy we found that the manatee retina has both rodlike and conelike photoreceptors in accord with its diurnal behavior pattern. Outer segment disks in both cell types appear to be enclosed along most of their length within the plasma membrane. The synaptic terminals are simple, with small, superficial postsynaptic contacts. The cones have long inner segments, short, conical outer segments and terminals with numerous synaptic ribbons and deeply embedded postsynaptic elements. There are two cone subclasses that may subserve color vision. Morphometry shows that there are more ganglion cells of small size ventrally, and that the thickness of the nerve fiber layer there is reduced, suggesting the presence of a specialized visual area in the retina. However, there were no pronounced differences in cone cell density in any of the regions examined.

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