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Summarized by Shirani Rajan April 20,2004

Switching Skeletons: Hydrostatic Support in Molting Crabs Jennifer R. A. Taylor and William M. Kier. Summarized by Shirani Rajan April 20,2004. Introduction. Crustaceans undergo periods in which they shed their exoskeleton.

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Summarized by Shirani Rajan April 20,2004

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  1. Switching Skeletons: Hydrostatic Support in Molting CrabsJennifer R. A. Taylor and William M. Kier Summarized by Shirani Rajan April 20,2004

  2. Introduction • Crustaceans undergo periods in which they shed their exoskeleton. • They typically spend the time in seclusion, but still maintain movement and activity. • This occurs by way of a hydrostatic support system. http://www.todayaqua.com/Aquafarming%20species %20and%20method/Crab%20farming/

  3. Definitions: • Rigid Skeleton Force derives from muscle contraction as there is a pull on rigid elements. • Hydrostatic System Force occurs through muscle contraction and the pressure in an incompressible fluid increases.

  4. Preliminary Experiment • Hypothesis: Internal hydrostatic pressure is essential to maintain structure. • Experiment: They removed a cheliped (joint structure) from a blue crab that had molted and allowed the fluid to drain. • Results: In accordance with prediction, the cheliped collapsed without hydrostatic pressure.

  5. Definitive Experiment • Hypothesis: When the shell is soft, pressure and force interact, but after the exoskeleton has hardened fully, hydrostatic pressure declines. • Experiment: They measured the pressure via a pressure transducer inserted into the hemocoelic fluid and a force transducer attached to the cheliped.

  6. Definitive Experiment • Results: Following exuviation (see graphs) 1 hr – Peaks of increased pressure associate with peaks of increased force; thus, hydrostatic support is involved. 12 hr – Similar peak coordination is observed; so even when the cuticle is complete, and hardening begins, the hydrostatic system is used.

  7. Definitive Experiment 7 dy – Increased force peak but absence of pressure increase indicates that since the cuticle is fully hardened it can counteract the force of muscle contraction and there is no longer a need for another support.

  8. Graphs of Data A B

  9. Discussion • To compensate for the lack of rigid structure when the crab undergoes molting, hydrostatic pressure is employed. • Hydrostatic pressure accompanies the force generated by the muscles and keeps the crab from buckling inwards, thus allowing free movement during the two softer-shell stages.

  10. Discussion • The lack of pressure in the hard stage coincides with the presence of the hard exoskeleton which is enough of a support. • The decrease in the amount of muscle force (graph B) initially after molting could be due to hydrostatic force acting as a limiting factor, but this does not incapacitate crustaceans.

  11. Interesting Note • Other organisms use hydrostatic mechanisms in organs along with their standard support system. • However, crustaceans are the only examples of organisms that alternate the mechanism of support for the entire body itself between the two types mentioned.

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