* Annelida (Segmented Worms): Earthworms, leeches, and other segmented worms use their internal fluid pressure and muscular contractions to move and change shape.
* Nematoda (Roundworms): These worms have a fluid-filled body cavity that provides support and allows for movement.
* Platyhelminthes (Flatworms): Flatworms lack a coelom, but their body is filled with mesenchyme, a type of tissue that acts as a hydrostatic skeleton.
* Cnidaria (Jellyfish, Corals, Anemones): These animals have a fluid-filled gastrovascular cavity that provides support and allows for movement.
* Mollusca (Snails, Slugs, Oysters, Squid): Some mollusks, particularly those with a soft body, like slugs and octopuses, rely on their internal fluid pressure for support and movement.
Note: While some organisms may have a hydrostatic skeleton, they may not have a soft body wall. For example, sea anemones have a hydrostatic skeleton but also have a hard exoskeleton.
Key characteristics of organisms with a hydrostatic skeleton:
* No hard skeletal support: The internal fluid pressure provides the structural support.
* Soft body wall: The body is flexible and can change shape.
* Muscular contractions: Muscles contract against the fluid pressure to create movement.
* Fluid-filled cavity: The body cavity is filled with fluid, often a coelom, gastrovascular cavity, or mesenchyme.
These organisms utilize their hydrostatic skeleton for various functions, including:
* Locomotion: Movement through contraction and relaxation of muscles.
* Support: Maintaining body shape and providing structural integrity.
* Feeding: Extending and retracting body parts for capturing prey.
* Defense: Changing body shape to deter predators.
Overall, a hydrostatic skeleton is a highly adaptable and efficient way for organisms to support and move their soft bodies.
