Answer :
Sea urchin belongs to phylum Echinodermata.
Any member of the phylum Echinodermata is considered an echinoderm. Adults with radial symmetry include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as sea lilies or "stone lilies."
Adult echinoderms can be found on the sea floor at any depth, from the intertidal zone to the abyssal zone. The phylum contains approximately 7,000 living species, making it the second-largest deuterostome grouping after chordates. Echinoderms are the largest phylum that is entirely marine. Near the beginning of the Cambrian period, the first definitive echinoderms appeared.
Sea urchins are spiny, globular echinoderms of the Echinoidea class. There are approximately 950 species of sea urchins that live on the seafloor of every ocean and inhabit every depth zone from the intertidal seashore to 5,000 meters.
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