Sea stars don't have a dedicated circulatory system like humans do with blood and veins. Instead, oxygen is moved around their body through a water vascular system.

Here's how it works:

* Seawater enters through madreporite: This is a small, sieve-like opening on the top surface of the sea star.

* Water flows through canals: The madreporite connects to a network of canals that run throughout the sea star's body.

* Tube feet: The water vascular system also powers the sea star's tube feet. These are small, muscular appendages that help the sea star move and feed.

* Oxygen diffusion: Oxygen is dissolved in the seawater and diffuses directly into the sea star's tissues through the canals and tube feet.

So, while not a circulatory system in the traditional sense, the water vascular system plays a vital role in oxygen transport for sea stars.