<span>The types of skeleton depend on where they are located. Earthworms have hydroskeleton because their rigid bodies are based on water pressure so it's hydro then. Endo is found in animals like birds and also humans who have it inside. Exo is found in spiders because they are bugs and bugs have their skeletons like a shell that covers them.</span>
This process requires large volumes of water to pass through absorption surfaces to get enough oxygen into their bodies using their mouths and gills. These body parts work like a pump to keep water moving over the gas absorption surfaces of the gills.
