Hopkins Marine Station Student Paper

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(full paper is archived in the Miller Library)

Title: Biomechanics of the tube foot-ampulla system in Pycnapodia helianthoides
Student Author(s): Magnuson, Leif L.
Faculty Advisor(s): Denny, Mark
Pages: 20
Location: Final Papers Biology 175H
Date: June 1984
Keywords: movement
Abstract: This study attempts to correlate mechanical characteristics of the tube feet and ampullae in Pycnopodia helianthoides with filmed behaviour of the tube foot-ampulla system in operation. The tube foot-ampulla system is an isovolumetric system. Tube foot wall thickness increases during contraction (E = 0.5 at 54% extension). Tube feet at maximum contraction lose about 88% of their extended volume. The ampullae simulataneously expand in volume by roughly 1110% Longitudinal and circular fibers were found in the ampulla. The maximum strain for these fibers is a s yet undetermined, but what limits tube foot contraction is more likely the maximum contractility of tube foot longitudinal muscles. Tube foot extension is limited by contraction of the ampulla (i.e. restricted by total internal volume of the system). Helically unmapped fibers in the tube foot greatly enhance its extensile capability.