echinoderm

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echinoderm Phylum of spiny-skinned marine invertebrate animals. Radially symmetrical with five axes, their skin consists of calcareous plates. Their hollow body cavity includes a complex, internal fluid-pumping system and tube feet. They reproduce sexually, and produce a bilaterally symmetrical larva resembling that of chordates; regeneration also occurs. Species include sea urchin, sea cucumber, and starfish.

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