Hydra has no specific respiratory organs. It causes the exchange of gaseous substances through the epidermis and gastrodermis.
1. Epidermis: Dissolved oxygen from the water around the body enters the epidermal cells by diffusion. The absorbed oxygen reaches the various cells of the body and completes the respiration process. Carbon dioxide produced as a result of respiration is released outside the body in the process of diffusion. Dr. Siddiq Publications
2. Gastrodermis: Gastrodermis consists of flagellated cells. Flagellar movement causes a constant flow of water into the stomata. Dissolved oxygen from water enters the gastrodermal cells by the process of diffusion. The absorbed oxygen reaches the various cells of the body and completes the respiration process. Carbon dioxide produced as a result of respiration is released outside the body in the process of diffusion.
