Publication: Fine structure of the tapetum lucidum in the short-tailed stingray Dasyatis brevicaudata
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Date
1994
Authors
Braekevelt, Charlie R.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The tapetum lucidum of the short-tailed
stingray (Dasatis brevicaudata) is located in the choroid
of the superior fundus immediately external to the
choriocapillaris. In this species the tapetum consists of a
single layer of overlapping cells oriented at an angle of
about 30" to the incoming light. These tapetal cells
alternate with and are separated from one another by
melanocytes which extend beyond the tapetal cells to
intervene between the tapetal cells and the choriocapillaris.
The tapetal cells and the melanocytes are
flattened plate-like cells with their widest dimension
facing the retina. Internally the tapetal cells display a
peripherally located vesicular nucleus with most
organelles in a paranuclear location. The bulk of the cell
is packed with regularly spaced crystals reported to be
guanine. The size and spacing of these reflective crystals
is commensurate with constructive interference. In lightadaptation,
the melanosomes of the intervening
melanocytes are widely dispersed and for the most part
block the passage of light to the tapetal cells. Although
dark-adapted specimens were not examined, it seems
reasonable to assume that in dark-adaptation, the
melanosomes will retreat to unmask the tapetum and
allow it to function as a reflective layer.
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