hydrostatic skeleton


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hydrostatic skeleton

a liquid, usually water, that maintains the shape of an organism such as an earthworm by filling internal spaces. see SKELETON.
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Hollow, cylindrical muscular organs and bodies are widespread in animals and are used for movement, locomotion, burrowing, and pumping, with support provided by a hydrostatic skeleton (1, 2).
They have a hydrostatic skeleton in which the skin and muscles are under pressure to allow the animal to stay semi-rigid, so when you jab a worm with a needle it will, in effect, explode.
Octopuses lack bones, so they rely on a hydrostatic skeleton, which uses water pressure instead of bones, to prop themselves up and give their arms strength.
Once a clade evolves a lever-skeleton and gives up the hydrostatic skeleton, it has the potential to live in a wide range of adaptive zones that were previously inaccessible to it (see below), but it can no longer do without the hard lever-skeleton.