Sea urchins are invertebrate sea creatures that live in the shallow zones of oceans all over the world and vary in color. Similar to sea stars, sea urchins have a water vascular system. Their spherical shape is typically small, ranging from about 3 cm to 10 cm in diameter, and their bodies are covered with a spiny shell. The skeleton of a sea urchin is also known as the test. The shells within the test of these creatures are made up of packed, fitted plates which protect them from being damaged. As for the spines outlining their shell, these are movable and help the sea urchin to camouflage or protect itself from predators.
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