1 In the medusae of Cnidaria, an arrangement of the gut cavity; the mouth leads to the stomach, hanging from the centre of the umbrella, from where canals (typically there are four) extend to the outer rim of the umbrella where they are linked by a ring canal around the periphery.
2 In Echinodermata, ciliated canals, forming part of the water-vascular system, that extend from the stone canal (or ring canal or water ring) into each arm, passing along the oral side of the ambulacral groove (see ambulacrum) and ending in a small, external tentacle.
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