Development of the tentacles and food groove in the jellyfish Aurelia aurita (Cnidaria: Scyphozoa)

The development of the tentacle-bearing part of the rim of the jellyfish Aurelia aurita is described. The newly liberated ephyra lacks appendages at the bell rim between the rhopalial arms (null stage). The next stage (bump stage) has a subumbrellar bump near the rim. The bump then forms a tongue process (tongue stage) on its adoral side. The aboral part of the bump becomes the primordium of the tentacle. The tongue process elongates and spreads circumferentially, finally melding with the lappets of the rhopalial arms. Next the tongue process develops a groove that spreads laterally. The epithelium of the groove becomes glandular and serves as a food groove where particulate matter such as plankton is concentrated and undergoes the initial phase of digestion. The "upper" side of the split tongue process becomes the floor of the tentacle chambers, while the "lower" side becomes the pseudovelarium. The growth and differentiation zone for the medusa's rim is at the junction of the tentaculate part of the rim with the rhopalial region. It is here that tentacle buds form, followed by intertentacular lappets (partitions).