The water vascular system is a hydraulic system used by echinoderms, such as starfish and sea urchins, for locomotion, food and waste transportation, and respiration^[1]. 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^[1][2]. Classes Subphylum Homalozoa Gill & Caster, 1960 Class Homostelea Class Homoiostelea Class Stylophora Gill & Caster, 1960 Class Ctenocystoidea Robison & Sprinkle, 1969 Subphylum Crinozoa Class Eocrinoidea Jaekel, 1899 Class Paracrinoidea Regnéll, 1945 Class Cystoidea von Buch, 1846 Class Blastoidea Class Crinoidea Subphylum Asterozoa Class Ophiuroidea Class Asteroidea Subphylum Echinozoa Helicoplacoidea †  ?Arkarua... Orders Brisingida (100 species[1]) Forcipulatida (300 species[2]) Paxillosida (255 species[3]) Notomyotida (75 species[4]) Spinulosida (120 species[5]) Valvatida (695 species[6]) Velatida (200 species[7]) For other uses, see Starfish (disambiguation). ... Subclasses Subclass Perischoechinoidea Order Cidaroida (pencil urchins) Subclass Euechinoidea Superorder Atelostomata Order Cassiduloida Order Spatangoida (heart urchins) Superorder Diadematacea Order Diadematoida Order Echinothurioida Order Pedinoida Superorder Echinacea Order Arbacioida Order Echinoida Order Phymosomatoida Order Salenioida Order Temnopleuroida Superorder Gnathostomata Order Clypeasteroida (sand dollars) Order Holectypoida Wikispecies has information related to... In animal physiology, respiration is the transport of oxygen from the ambient air to the tissue cells and the transport of carbon dioxide in the opposite direction. ...

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^[3]. Small red or yellow button-like structure that often looks like a small wart on a sea stars central disk. ... The ampulla of Vater is a sphincter (a small muscle) where the common bile duct enters the duodenum. ...

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