ABSTRACT
The “catch apparatus” is by now a well established phenomenon in all classes of echinoderms. This chapter summarizes the results of stress relaxation experiments conducted on body wall tissues from several species of holothurians. First, during short term relaxation the tissue behavior can be modelled as two parallel Maxwell elements, each consisting of an elastic component and a viscous component in series. Second, the principle mechanical changes associated with the state of “catch” occur in the viscous component of the second Maxwell element. Third, interstitial calcium ion concentration appears to have a role in regulating the “catch” state. The mucopoly-saccharide matrix is a network of randomly coiled polymers cross-linked to each other at discrete bond sites. When the tissue is deformed the matrix undergoes a reduction in conformational entropy which manifests itself as an elastic restoring force, a phenomenon known as entropy elasticity.
