Capstone Title

A Comparative Analysis of Life History and Alimentary Canal Morphology and Physiology in Elasmobranchii and Acipenseriformes

Defense Date

6-2009

Document Type

Capstone

Degree Name

M.S. Marine Biology

First Advisor

Robin L. Sherman

Second Advisor

Richard E. Spieler

Abstract

Elasmobranchii and Acipenseriformes are two ancient, yet highly derived groups of cartilaginous fishes with trophic dynamics ranging from planktivore to carnivore, habitat distributions ranging from the northern hemisphere to circumglobal, and widely varied reproductive strategies. Although largely structurally similar to other vertebrates, they exhibit a unique adaptation within the alimentary canal found only in ‘primitive’ fishes, the spiral valve intestine.

In both groups, physiological functions of the alimentary canal are consistent with primary digestion taking place in the cardiac stomach and primary absorption taking place in the spiral valve intestine. A key difference in the alimentary canal between Elasmobranchii and Acipenseriformes is the presence of a well-developed pyloric caecum in the latter. Although the number of turns in the spiral valve is species specific, the effect of the structure is to increase the surface area of the spiral intestine by at least 3-fold compared to a linear intestine of the same physical length.

Additionally, although exhibiting very different modes of reproduction, both groups require a great deal of space within the body cavity for reproduction thus limiting space available for the organs of the alimentary canal. The spiral valve intestine creates the needed surface area for digestion and absorption while maintaining a compact structure.

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