Water vascular system
The water vascular system is a hydraulic system used by
The exact structure of the system varies somewhat between the five classes of echinoderm. The system is part of the coelomic cavities of echinoderms, together with the haemal coelom (or haemal system), perivisceral coelom, gonadal coelom and perihaemal coelom.[3]
Other terms sometimes used to refer to the water vascular system are "ambulacral system"
Sea stars
In
Each side of the radial canals gives rise to a row of bulb-like ampullae, which are connected via lateral canals. In sea stars these are always staggered, so that an ampulla on the left follows one on the right, and so on down the length of the radial canal. The ampullae are connected to suckerlike podia. The entire structure is called a
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.[12]
The central ring canal, in addition to connecting the radial canals to each other and to the stone canal, also has a number of other specialised structures on the inner surface. In between each radial canal, in many sea star species, there lies a muscular sac called a
Although the contents of the water vascular system are essentially
Ophiuroids
Ophiuroids have no ambulacral groove, and the radial canals instead run through the solid bone-like ossicles of the arms. Unlike sea stars, the tube feet are paired instead of staggered, and there are no ampullae. Instead, a simple valve at the upper end of the foot helps to control water pressure in the tube feet, along with contraction of the associated canals.[11]: 957
Sea urchins
The madreporite of
The ampullae branching off from either side of the radial canals give rise to ten rows of tube feet, which penetrate through holes in the test to the outside. As in sea stars, the ampullae are arranged alternately, but in most (though not all) cases they split into two as they pass through the test before merging again on the outer side. The tube feet of sea urchins are often highly modified for different purposes. The radial canal ends in a small water-filled tentacle which protrudes through the uppermost plate of the ambulacral region.[11]: 972–973
Crinoids
Uniquely among echinoderms,
The five radial canals run into the arms and branch several times to supply all of the individual branches and pinnules lining the arms. As in other echinoderms, the radial canals give rise to lateral canals, but there are no ampullae, and clusters of three tube feet branch from the ends of each canal, except around the mouth, where they are found singly. In the absence of ampullae, water pressure is maintained by the ring canal, which is surrounded by contractile
Sea cucumbers
The water vascular system of sea cucumbers has no connection to the outside, and is thus filled with the internal coelomic fluid, rather than sea water. The madreporite is present, but lies within the body cavity, just below the pharynx. The stone canal is relatively short.[11]: 991–992
The ring canal normally has one to four polian vesicles, but in the order Apodida, there may be as many as fifty. The radial canals run through notches in the calcareous plates surrounding the mouth and then run along the ambulacral areas along the length of the body. Lateral canals run to both the tube feet and the large oral tentacles, all of which possess ampullae. The Apodida, which have no tube feet, also have no radial canals, with the canals to the tentacles branching off directly from the ring canal.[11]991–992
References
- ^ a b Solomon, Eldra; Linda Berg; Diana Martin (2002). Biology. Brooks/Cole.
- ^ Dale, Jonathan (2000). "Starfish Science".
- ^ "Macrobenthos of the North Sea - Echinodermata > Introduction". etibioinformatics.nl.
- ^ Encyclopædia Britannica. Vol. 08 (11th ed.). 1911. .
- ^ Harrison, F.W. & Chia, F.-S. (1994). Microscopic Anatomy of Invertebrates. Vol. 14: Echinodermata. Wiley-Liss, New York, [1].
- ^ Ax, Peter. (2003). Multicellular animals: the phylogenetic system of the metazoa. Akademie der Wissenschaften und der Literatur, Mainz, vol. 3., [2].
- ^ Carpenter, William Benjamin (1854). Principles of comparative physiology. 4th ed. London: John Churchill, [3].
- ^ Siebold, C.Th. von (1874). Anatomy of the Invertebrata. Translated by W.I. Burnett. Boston: J. Campbell, [4].
- ^ Bergquist, Patricia R. (1978). Sponges. London: Hutchinson, [5].
- ^ Voltzow, J. (1994). Gastropoda: Prosobranchia. In: Microscopic Anatomy of Invertebrates, Harrison, F.W. & Kohn, A.J. (eds.), Vol. 5: Mollusca I. Wiley-Liss, New York: 111–252, [6].
- ^ ISBN 0-03-056747-5.
- ISBN 0-07-237716-X.