Thesis (Ph. D.)--Auburn University. / Abstract. Includes bibliographical references.

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Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Electrophysiological recordings were made from the radial nerve cord of the brittlestar Ophiura ophiura in response to stimulation by certain environmental parameters. Extracellular suction electrodes attached to the ectoneural portion of the radial nerve cord recorded unitary potentials in response to photic, mechanical and chemical stimulation. O. ophiura is highly sensitive to reductions in the ambient light level or shadow, the greatest response being to the rapid onset of a dense shadow on the tip of the arm. Parallel behaviour studies indicate that this same stimulus resulted in the cessation of any type of activity in the unrestrained animal. The "freezing" of the brittlestars movements at the onset of such a shadow stimulus, is suggested to be a means of escaping detection by a predator. The range that the brittlestar is able to detect in the mechanical mode extends from the nearfield of a vibrating source, through the far field propagated pressure wave, to movement of the aquatic medium as a whole in the form of water currents. The behavioural responses of unrestrained animals to stimulation in the same frequency range is described. The presence of an interoreceptor located within the spines, which is responsible for some mechanical sensitivity is inferred from electrophysiological recordings in response to the movement of individual arm spines. Using neurophysiological techniques, O. ophiura could be shown to detect consistently a range of amino acids at concentrations as low as 2 X 10^-12M. as in the case of L-Leucine. Parallel behaviour experiments were inconsistent and indicate the inadequacies of using behavioural criteria to demonstrate the sensory discriminatory abilities of echinoderms. An anatomical study of the podia, spines and general surface of O. ophiura using the scanning and transmission electron microscopes, describe various types of ciliated cells which may function as receptors. The relationship of these structures to the sensory abilities of the brittlestars detected physiologically is described.

No description available.

Thesis (Ph.D.)--University of North Carolina Wilmington, 2008. / Title from PDF title page (viewed May 27, 2009) Includes bibliographical references (p. 73-76)

Gorgonocephalus eucnemis, Ophiothrix suensonii and Ophiothrix spiculata are aerobic Echinoderms. Previous observations on the anatomy of these two genera state five pairs of radial shields and genital plates are responsible for regulating the position of the roof of the body disc and the flushing of water in and out of the bursae. Rates of bursal ventilation increase by an average 60-64% when the ophiuroid is exposed to an increase in food or a decrease in dissolved oxygen in Gorgonocephalus. When exposed to hypoxic oxygen concentrations O. suensonii and O. spiculata increased bursal-ventilation rates by (means of) 35% and 28%. Measurements of DO from inside and outside the bursae show that DO is being absorbed during bursal-ventilations. These findings suggest bursal ventilation is a means of respiration and increased rates of bursal-ventilation may help meet increased oxygen demands during feeding and some periods of hypoxia. This dissertation includes unpublished, co-authored material.