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EncyclopediaEchinodermataEchinodermata (ukī"nōdûr'mutu) [key][Gr.,=spiny skin], phylum of exclusively marine bottom-dwelling invertebrates having external skeletons of calcareous plates just beneath the skin. The plates may be solidly fused together, as in sea urchins, loosely articulated to facilitate movement, as in sea stars (starfish), or reduced to minute spicules in the skin, as in sea cucumbers. The skin usually has warty projections or spines, or both. Echinoderms display pentamerous radial symmetry, that is, the body can be divided into five more or less similar portions around a central axis. Unlike other radially symmetrical animals, they develop from a bilaterally symmetrical larva and retain some degree of bilateral symmetry as adults. There is no head; the surface containing the mouth (the underside, in sea stars and most others) is called the oral surface, and the opposite side, which usually bears the anus, the aboral surface. There are five living classes of echinoderms. Sections in this article: The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2007, Columbia University Press. All rights reserved. More on Echinodermata from Infoplease:
- Echinodermata: Class Ophiuroidea - Class Ophiuroidea The brittlestars, or serpent stars, are so called for their long, slender, ...
- Echinodermata: Class Echinoidea - Class Echinoidea Echinoids—sea urchins, heart urchins, and sand dollars—are echinoderms ...
- Echinodermata: Class Asteroidea - Class Asteroidea Sea stars, or starfish, vary in shape from nearly circular, to pentagonal, to the ...
- Echinodermata: Class Holothuroidea - Class Holothuroidea The sea cucumbers are long-bodied echinoderms with the mouth at or near one end ...
- Echinodermata: Anatomy and Physiology - Anatomy and Physiology The radially symmetrical body cavity contains a system of water-filled ...
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