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Blue crab hours after molting
A blue crab (Callinectes sapidus) two hours after molting. Even though the old rigid external skeleton has been shed, this "soft-shell" crab is still capable of forceful movement. Simultaneous measurements of force and internal pressure suggest that the soft, water-inflated body may rely on a hydrostatic skeletal support system similar to that of worms. Thus, the animal alternates between rigid and hydrostatic skeletons as it grows.
Invertebrate musculoskeletal systems are the focus of ongoing studies in the lab of William M. Kier, a professor in the Biology Department at the University of North Carolina at Chapel Hill, and supported in part by the National Science Foundation. Hydrostatic skeletal support systems have been a particular focus of Kier's work. [See Taylor, J.R.A. and Kier, W.M. (2003) Switching Skeletons: Hydrostatic Support in Molting Crabs. Science 301: 209-210.] (Year of image: 2003)
Credit: William M. Kier, Department of Biology, University of North Carolina at Chapel Hill
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