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Animal Health

How does the water vascular system of a sea star work?



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The system is composed of canals connecting numerous tube feet. Echinoderms move by alternately contracting muscles that force water into the tube feet, causing them to extend and push against the ground, then relaxing to allow the feet to retract.

Water enters madreporite and flows through the stone canal and then enters the circular ring canal. Water then is separated into five radial canals that branch into double rows of bulblike structures called ampullae, which are on each side of the ambulacral ridge. The ampullae are connected to suckerlike podia, the entire structure is called a tube foot. Contraction of the ampullae causes the podia to stretch as water is brought into them. This whole process allows for movement, and is quite powerful but extremely slow.

"Madreporite" is another way to say "Sieve Plate"