[Cubo-/Scyphomedusae] In rhizostome medusae, a genital ostium (pl., ostia) is a gap between adjacent mouth-arm bases, proximal to their point of fusion. The basal regions of the mouth arms are in that region termed “ pillars” in distinction from the ostia between. The relative widths of these pillars and gaps are diagnostic of certain genera and species. Variously-shaped papillae (genital papillae) project into the ostia in the suborder Daktyliophorae from the subumbrella epidermis, partly closing the aperture. The genital cavity onto which the ostia open was formerly known as the genital porticus (e.g. Mayer, 1910, p. 632).

Alternative forms for Genital ostium : genital papilla, genital pillar, genital porticus.