What type of skeletion is composed of muscle and fluid?

The type of skeleton composed of muscle and fluid is known as a hydrostatic skeleton. This system is found in many soft-bodied animals, such as jellyfish and earthworms, where the body is supported by the pressure of fluid within a cavity. Muscles contract against this fluid-filled cavity, allowing for movement and shape changes. Hydrostatic skeletons provide flexibility and adaptability in various environments.