What is a starfish's ring canal?

A starfish’s ring canal is part of its water vascular system. The ring canal serves as a water pump that distributes water to its five radial canals that go to its individual tube feet.

The water vascular system of a starfish runs from the aboral madreporite, where seawater is pumped into the water vascular system by cilary action. The seawater then goes through the stone canal and then to the ring canal. The five tubes to which the ring canal pumps seawater are comprised of a hollow muscular structure that is attached to a fluid reservoir, similar to a balloon, called the ampulla.