Notes

Echinoderms are slow-moving or sessile marine animals. This phyla includes animals like sea stars (starfish). This phyla has a unique organization of organs called the water vascular system, a network of canals eventually branching into tube feet.
The water vascular system is responsible for starfish for locomotion, food, waste transportation, and respiration. However, starfish do not actually need to osmoregulate as they are osmoconformers. This phyla have body fluids that have a similar osmolarity as the seawater that surrounds them so they gain and lose water at equal rates and have no need to expend energy expelling water or salt from the body.
What are the different parts of the water vascular system, and how are they connected to each other?
The external opening to the water vascular system is the madreporite, connected to the stone canal and connected to the ring canal surrounding the oral opening. Radial canals extend from the ring canal down each arm, or ambulacral groove, and are connected to lateral canals, and in turn, the tube feet. Each tube foot has an internal ampullae and external podium and can be isolated from the rest of the water vascular system by a valve at the junction of the tube foot and the lateral canal. Tiedemann’s bodies and polian vesicles are often connected to the ring canal.