TAYLOR, J.R.A.*; KIER, W.M.; University of North Carolina, Chapel Hill; University of North Carolina, Chapel Hill: Hydrostatic Skeletons in the Crustacea

The crustacean molt cycle involves a short phase, ecdysis, in which the animal sheds its rigid exoskeleton and is left with a soft, flexible cuticle inflated with water. During the few days required for the new cuticle to harden, it�s often presumed that the animal is immobile. On the contrary, recently molted animals are capable of crawling, swimming, and other vigorous movements. My research investigates how crustaceans maintain locomotor ability after the loss of their rigid skeletal support system. Specifically, I hypothesize that crustaceans use a hydrostatic skeleton, a form of skeletal support common in soft-bodied organisms. In a hydrostatic skeleton, an incompressible volume of fluid in a tension-resisting container transmits the force of muscle contraction. Thus, muscle contraction causes an increase in hydrostatic pressure. To test for hydrostatic support, I measured simultaneously the internal hydrostatic pressure and force exerted by the cheliped of newly molted blue crabs, Callinectes sapidus. A strong correlation was observed between the force exerted by the cheliped during muscle contraction and the hydrostatic pressure in the cheliped. In general, large peaks of force were tightly correlated with large peaks of pressure. Furthermore, crabs measured in late postmolt, after the new cuticle is hardened, show large peaks of force but no corresponding increase in pressure. These results are consistent with the hypothesized hydrostatic skeletal support system and suggest that Crustacea have the unique capability of repeatedly alternating between two major forms of skeletal support. Studies of muscle and cuticle mechanical properties are planned to further elucidate hydrostatic skeletal support in the Crustacea. Supported by NASA grant NAG5-8759 and NSF grant IBN-972707 to W. M. Kier.