Hydrostatic skeleton

Flexible skeleton supported by fluid pressure

A hydrostatic skeleton or hydroskeleton is a type of skeleton supported by hydrostatic fluid pressure or liquid, common among soft-bodied invertebrate animals colloquially referred to as "worms". While more advanced organisms can be considered hydrostatic, they are sometimes referred to as hydrostatic for their possession of a hydrostatic organ instead of a hydrostatic skeleton, where the two may have the same capabilities but are not the same. As the prefix hydro- meaning "water", being hydrostatic means being fluid-filled.

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