[Cnidaria] In most Antho- and Leptomedusae, a dilated portion of the proximal part of a marginal tentacle, next to umbrella margin, containing a cavity in communication with the circular canal and with the tentacular cavity of hollow tentacles. Of various shapes, most simple but in some medusae compound, originating several tentacles (e.g., Bougainvillia); performing digestive activities; centres of cnidoblast formation and, in some species, bearing ocelli. In Anthomedusae and Leptomedusae a new marginal tentacle is normally preceded by the formation of a bulb on which it will develop (see marginal bulb). In some medusae there are no true tentacular bulbs: i.e. in the Limnomedusae, Narcomedusae, Trachymedusae, in the majority of the Bythotiaridae, and in two species of Anthomedusae.

Alternative form for marginal tentacle bulb : tentacular marginal bulb.