sea urchin

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sea ur·chin • n. a marine echinoderm that has a spherical or flattened shell covered in mobile spines, with a mouth on the underside and calcareous jaws. Several families and genera and numerous species include the Atlantic purple sea urchin (Arbacia punctulata, family Arbaciidae).

sea urchin

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sea urchin Spiny echinoderm animal found in marine tidal pools along rocky shores. Round with long, radiating (often poisonous) moveable spines, its skeletal plates fuse to form a perforated shell. Class Echinoidae.