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Fluid pressure provides support: blue crab


Atlantic Blue Crab / Wendy Kavene.. / LicenseCC-by-sa - Attribution Share Alike

The body of the blue crab functions during exoskeletal molt using hydrostatic pressure.

"The aquatic blue crab Callinectes sapidus maintains mobility by switching to a hydrostatic skeleton 10 — a fluid-based skeleton that is common in soft-bodied invertebrates 11. Hydrostatic skeletons are arranged so that the force of muscle contraction is transmitted by an essentially incompressible aqueous fluid 11–13. Muscle contraction increases the pressure in the fluid, causing the deformations or stiffening required for support, movement and locomotion." (Taylor and Kier 2006:1005)

"Like vertebrates, crustaceans usually move their limbs using muscles attached to a hard skeleton--albeit one on the outside of the body rather than the inside. But when a crab sheds its skeleton to grow a bigger shell, the muscles are left without any rigid surface to pull against. How do they do it? William Kier and Jennifer Taylor of UNC-Chapel Hill investigated, and found that, during molting, crabs use hydrostatic pressure to create a stiff structure against which muscles can pull. Fluid pressure in the claw goes up as the muscles contract; if you remove a claw during molting, it deflates like a flat tire. Once the shell has hardened, however, pressure does not change during muscle use. Soft-shelled crabs are the first animals known to use both a skeleton and hydrostatic pressure for support." (Jones 2003:17)
About the inspiring organism
Med_atlantic_blue_crab bluepoint
Callinectes sapidus M. J. Rathbun, 1896
Common name: blue crab

Learn more at
Some organism data provided by: ITIS: The Integrated Taxonomic Information System
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

IUCN Red List Status: Unknown

Bioinspired products and application ideas

Application Ideas: Hydrostatic skeletal support, hydrostatic "forms" for concrete.

Industrial Sector(s) interested in this strategy: Construction, packaging, transportation, manufacturing

The Kier Lab
William Kier
University of North Carolina Chapel Hill
Taylor, J. R. A.; Kier, W. M. 2006. A pneumo-hydrostatic skeleton in land crabs. Nature. 440(7087): 1005.
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Jones N. 2003. Soft-shelled crabs get all pumped up. New Scientist. 179(2404): 17.
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