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The contractile vacuole allows free-living protists to expel extra water. <b>The contractile vacuole allows free-living protists to expel extra water <br /></b>.
The Turbellaria are the only free-living group, meaning that they can be found wandering around in the general environment. Turbellarians are aquatic (water-living), crawling around mostly on surfaces at the bottoms of bodies of water. Planaria, a common animal in laboratory exercises, is a turbellarian.