What is "water vascular system"

Vascular \Vas"cu*lar\, a. [L. vasculum a small vessel, dim. of vas vessel: cf. F. vasculaire. See Vase, and cf. Vessel.]

1. (Biol.)

   1. Consisting of, or containing, vessels as an essential part of a structure; full of vessels; specifically (Bot.), pertaining to, or containing, special ducts, or tubes, for the circulation of sap.

   2. Operating by means of, or made up of an arrangement of, vessels; as, the vascular system in animals, including the arteries, veins, capillaries, lacteals, etc.

   3. Of or pertaining to the vessels of animal and vegetable bodies; as, the vascular functions.

2. (Bot.) Of or pertaining to the higher division of plants, that is, the ph[ae]nogamous plants, all of which are vascular, in distinction from the cryptogams, which to a large extent are cellular only.

   Vascular plants (Bot.), plants composed in part of vascular tissue, as all flowering plants and the higher cryptogamous plants, or those of the class Pteridophyta. Cf. Cellular plants, Cellular.

   Vascular system (Bot.), the body of associated ducts and woody fiber; the fibrovascular part of plants.

   Vascular tissue (Bot.), vegetable tissue composed partly of ducts, or sap tubes.

   Water vascular system (Zo["o]l.), a system of vessels in annelids, nemerteans, and many other invertebrates, containing a circulating fluid analogous to blood, but not of the same composition. In annelids the fluid which they contain is usually red, but in some it is green, in others yellow, or whitish.

n. system of fluid-filled tubes used by echinoderms in locomotion and feeding and respiration

The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. 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.

The exact structure of the system varies somewhat between the six classes of echinoderm.