THE MECHANICAL PROPERTIES OF THE AUTOTOMY TISSUES OF THE HOLOTHURIAN EUPENTACTA QUINQUESEMITA AND THE EFFECTS OF CERTAIN PHYSICO-CHEMICAL AGENTS

Evisceration in the holothurian Eupentacta quinquesemita (Selenka) results from a rapid softening of autotomy structures comprised of connec-tive tissue. The mechanical properties of two autotomy tissues, the introvert and the retractor muscle tendon, were tested to investigate their function in the non-evisceration state and their behaviour during autotomy. The results show that these structures do not have a pre-existing mechanical weakness to account for their rapid failure during evisceration. The autotomy res-ponse was mimicked in vitro by increasing K+ concentration. The introvert exhibited viscous behaviour and the absence of Ca2+ and Mg2"1 " decreased introvert viscosity, whereas excess Ca2+, and low and high pH, increased viscosity. These agents may influence the mechanical properties of the autotomy structures by directly affecting connective tissue ionic interactions and may induce proteoglycan conformational changes. K+ may also exert an indirect effect through responses of cells controlling connective tissue tensil-ity. The most likely mechanism of autotomy is through an alteration of connective tissue ionic interactions