The gastrodermis is the inner layer of cells that lines a gastrovascular cavity of Cnidarians. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Gastro vascular cavity, as the name indicates functions in both Digestion and Gas exchange. Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments
Zooxanthellae are unicellular yellow-brown (dinoflagellate) algae which live symbiotically in the gastrodermis of reef-building corals (Goreau et al. , 1979)