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Echinoderm
Phylum
Echinodermata
Any of numerous radially symmetrical marine invertebrates of the phylum Echinodermata, which includes the starfishes, sea urchins, and sea cucumbers, having an internal calcareous skeleton and often covered with spines.
[American Heritage Dictionary]
The word Echinoderma is derived from two Greek words, echino, a hedgehog, and derma, meaning skin.
This refers to the fact that their skeleton consists of calcareous plates with projecting spines imbedded in the skin.
Another distinctive characteristic is the possession of a radial symmetry or starlike pattern, instead of the bilateral or elongae symmetry of all other
animals above the Coelentera.
[
Field Book of Seashore Life
]
Classes of Phylum Echinoderm
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