Ion-dependent Viscosity of Holothurian Body Wall and its Implications for the Functional Morphology of Echinoderms

Abstract

Dermis from the holothurian Thyone inermis was subjected to constant load and its rate of plastic deformation (creep) was used to calculate tissue viscosity. During these tests the material was bathed in distilled water, sea water, or solutions of sodium, potassium, calcium, and magnesium salts in various combinations. Distilled water caused a threefold increase in viscosity which was reversed by sea water. Sodium and potassium decreased viscosity, while calcium and magnesium in combination with sodium increased it. Ionic cross-links shielded by monovalent ions but facilitated by divalent cations are proposed to explain this behaviour, and the relationship between this and other anomalies of echinoderm connective tissue physiology is discussed.