The sea urchin is part of the echinodermata phylum and the echinozoa subphylum. The sea urchin breathes through the gills and tube feet. Most sea urchins have five pair of gills near it's mouth. Fluid can be pumped through the gill by muscles. Also, sea urchins can breath through the use of tube feet in a process known as the water vascular system. The water vascular system moves water throughout their body, bringing in oxygen during the process.
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