Hydrostatic support describes the skeletal system of soft-bodied animals. These animals lack a firm skeleton such as ours. Instead of a skeletal system, these animals have what we call Hydrostatic skeleton. The fluid pressure and volume inside these animals remain constant since fluids are incompressible, unlike gases and solids. Therefore when the muscles of these animals contract and relax, the fluid inside just follows the shape of the vessel without any changes in pressure and in volume thereby allowing movement to occur.
