[ih-kahy-nuh-durm, ek-uh-nuh-]
any marine animal of the invertebrate phylum Echinodermata, having a radiating arrangement of parts and a body wall stiffened by calcareous pieces that may protrude as spines and including the starfishes, sea urchins, sea cucumbers, etc.

1825–35; taken as singular of Neo-Latin Echinodermata, neuter plural of echinodermatus < Greek echîn(os) sea urchin + -o- -o- + -dermatos -dermatous Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
echinoderm (ɪˈkaɪnəʊˌdɜːm)
any of the marine invertebrate animals constituting the phylum Echinodermata, characterized by tube feet, a calcite body-covering (test), and a five-part symmetrical body. The group includes the starfish, sea urchins, and sea cucumbers

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1835, from Mod.L. Echinodermata, from Gk. ekhinos "sea urchin," originally "porcupine, hedgehog" + derma (gen. dermatos) "skin;" so called from its spiky shell.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
echinoderm   (ĭ-kī'nə-dûrm')  Pronunciation Key 
Any of various marine invertebrates of the phylum Echinodermata, having a latticelike internal skeleton composed of calcite and usually a hard, spiny outer covering. The body plans of adult echinoderms show radial symmetry, typically in the pattern of a five-pointed star, while the larvae show bilateral symmetry. Echinoderms probably share a common ancestor with the hemichordates and chordates, and were already quite diversified by the Cambrian Era. They include the starfish, sea urchins, sand dollars, holothurians (sea cucumbers), and crinoids, as well as thousands of extinct forms.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
Even true immortality to accomplish this they would have to resemble echinoderms, such as sea urchins, except much more high-tech.
It is not known whether all of these echinoderms have been infected with the same etiologic agent.
These squishy invertebrates are echinoderms, making them distant relatives to starfish and urchins.
Articulata are stalked echinoderms with pentamerous symmetry.
Image for echinoderms
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