[Hydromedusae] Canals in medusae leading from the perradial corners of the manubrium to the circular canal. Usually they are straight and narrow with smooth sides, but in some species they are large, ribbon-like (e.g., Amphinema), and with a jagged outgrowth (e.g., Leuckartiara). Their typical number is four, but can be higher in many medusae, up to more than a hundred (e.g., Aequorea). They are normally simple, but can be branched in some species, the branches sometimes not reaching the circular canal (e.g., Staurodiscus). Generally the radial canals grow centrifugally, from the manubrium to the circular canal, except in a few species where growth is centripetal (e.g., Melicertum; the centripetal canals).

[Cubo-/Scyphomedusae] Canal leading between the stomach and the periphery of a medusa. In a few species, some radial canals originate from the periphery and end blindly without reaching the stomach. The branching patterns of the radial canals are used in many scyphozoan generic diagnoses. In many species a circular canal (= ring canal; sometimes termed primary circular or peripheral canal) links the outer ends of the radial canals at or near the margin. In a few, an intermediate circular (or ring) canal (mid-circular canal) occurs linking points mid-way along the radial canals (also termed the secondary circular canal). In many species the radial canals are partially linked laterally by an anastomosing network of branches, more or less orderly in arrangement, the intracircular canal network. In some species (e.g. Rhizostoma) the mid-circular canal is more developed than the peripheral canal, and by some authors (e.g. Russell, 1970) has been confusingly referred to as the "main canal" in view of its probable function.