A part of the water vascular system of echinoderms. Specifically, a circumoral ring around the esophogus with connecting radial canals each leading to an ambulacrum .It connects to the madreporite via the stone canal; also, the part of the distributive portion of the digestive system of scyphozoan medusae that is located in the margin of the bell. The ring canal communicates with the radial and adradial canals.