RELATIONSHIP BETWEEN FUNCTION AND MECHANICAL-PROPERTIES OF THE PLEOPODS OF ISOPOD CRUSTACEANS

In the isopod crustaceans Idotea wosnesenskii and I. resecata, the first three pairs of abdominal appendages (pleopods) are locomotory, and the remaining two pairs are respiratory. We investigated the mechanical and morphometric properties of the pleopods in order to study constraints that may influence this division of labor. Measurements of the flexural (bending) stiffness of the pleopods demonstrated that the podites of the first and second pairs of pleopods were generally an order of magnitude stiffer than the fourth and fifth pleopods; the third pleopods were variable in stiffness. Anterior pleopods tend to be slightly thicker and have thicker cuticles, but these morphological differences do not entirely account for differences in flexural stiffness among pleopods; there must also be differences in modulus of elasticity (E). Estimates of E based on these stiffness data yield values in the middle of the range typical of arthropod cuticles. The differences in cuticle thickness and material properties between the anterior and posterior pleopods may help explain why the swimming pleopods do not make a significant contribution to gas exchange.