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Sea urchins are small, spiny, ball-shaped creatures usually found on rocky ocean bottoms. Spines cover most of the sea urchin's body. These moveable spines are used for both walking along the ocean floor, and for protection from predators. Some sea urchin spines are also poisonous, to further protect against predators. Sea urchins have rows of tiny tube feet used to move along the ocean floor and collect food. On its underside is a claw-like mouth with five sharp teeth used to feed on algae or small invertebrates, such as mussels. Play the following videos to learn more about the sea urchin.