The gastrovascular cavity differs from the alimentary canal in that only the gastrovascular cavity has only a single opening. Gatrovascular cavity is the actual organ of digestion and circulation in the animal phyla Cnidaria and the Platyhelminthes. Alimentary canal unlike the gastrovascular cavity has two openings, the mouth on one end and the anus on the other end. Food goes in the mouth, while waste comes out the anus.