Theses and Dissertations

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Defense Date

2007

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Richard E. Spieler

Second Advisor

Robin Sherman

Third Advisor

Alois Lametschwandtner

Abstract

The yellow stingray, Urobatis jamaicensis, displays an aplacental viviparous mode of reproduction. Although each embryo is initially nourished only from a yolk sac, later trophonemata within the maternal uterus secrete histotroph to provide further nutritional sustenance. Histotroph in some stingray species is thick and may be ingested orally. However, the uterine fluid of U. jamaicensis remains thin and watery throughout gestation. It is hypothesized that the internal gill vasculature of U. jamaicensis embryos may be involved in nutrient uptake. The purpose of this study was to provide an anatomical basis for future physiological tests of this hypothesis. I examined the development of gill vasculature in the yellow ray throughout gestation. Corrosion casting with Mercox™ was utilized to create replicas of the vasculature within embryo gills and maternal uteri at various stages of gestation. Examination of these casts under scanning electron microscope revealed variation in the density of capillaries among trophonematal samples, though correlation of density with gestational stage could not be determined. The most marked changes in vascular configuration of the gills occur in the earliest castable stages of gestation. These changes included development of afferent external gill filament vessels and progression from paired dorsal aortae to a single fused dorsal aorta. Internal gill vasculature was found to nearly match that of an adult by the time the external gill filaments had fully regressed and yolk sac had been exhausted. Confirming the correlation that internal gill vasculature is fairly well developed by the time initial nutrient structures have regressed provides support for the hypothesis that these vessels may be involved in nutrient uptake in later stage embryos, providing sufficient surface for exchange. Physiological investigation is needed to examine their possible function in this role. Examination of embryo casts also revealed characteristics of the branchial vasculature not previously reported in adult specimens. These include the presence of prelamellar sph2 sphincters, intertrematic branches, afferent distributing arteries which supply blood to many afferent filament arteries, resulting in greater interconnection of the filaments, and observation that the afferent branchial artery in the first hemibranch supplies blood directly to the afferent filament arteries on the dorsal half of this arch.

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