The gastrovascular cavity is a structure found in primitive animal phyla. It is responsible for both the digestion of food and the transport of nutrients throughout the body. The cavity has only one opening to the environment. Food goes in and waste comes out that same opening, making it a two-way digestive tract.rimitive animals have body plans that are very different from ours. Animals such as jellyfish, corals and flatworms have a much simpler way to handle the digestion of food, as well as the circulation of nutrients around the body. Learn about the structure and function of the gastrovascular cavity in these organisms.