TAYLOR, J. R. A.*; KIER, W. M.; Univ. of North Carolina, Chapel Hill; Univ. of North Carolina, Chapel Hill: Mechanical properties of a crab skeleton following molting

Molting involves significant changes in the structure of the exoskeleton as the old one is shed and a new one is secreted. The flimsy new cuticle takes several days to harden and during this time crabs rely on a hydrostatic skeletal support system. This change from a rigid to a hydrostatic support mechanism implies correlated changes in function, and thus mechanical properties, of the cuticle, from primarily resisting compression and bending to resisting tension. This study was designed to describe changes in the mechanical properties of the cuticle following molting and to test the hypothesis that changes in the cuticle mechanical properties reflect the shift in skeletal support mechanism. The cuticle of the Blue crab, Callinectes sapidus, was examined at the following postmolt intervals: 1 hour (soft stage), 12 hours (paper stage), and 7 days (hard stage). Samples of cuticle were removed from the claw and the tensile strength was tested using an Instron. Soft stage cuticle had a maximum tensile breaking strength of 14 MPa, which was less than the paper stage cuticle (30 MPa) but greater than the hard stage cuticle (8 MPa). These data illustrate significant changes in mechanical properties of the cuticle as a consequence of the molt cycle. Currently, flexural stiffness is being tested in a 3 point bending apparatus and we predict that the hard stage cuticle will be orders of magnitude stiffer in bending than the paper and soft stage cuticle. The mechanical properties of the cuticle appear to correlate with the function of the cuticle in support; tensile strength is most important for hydrostatic support and flexural stiffness is most important for rigid support. Funded by NSF IBN-972707 and DARPA N66001-03-R-8043.