[Hydromedusae] Sometimes marginal bulbs without tentacles are developed on the umbrella margin. Either they never developed tentacles, or evolved by reduction of the tentacles. It is necessary to distinguish between bulbs which never have tentacles (permanent non- tentacular marginal bulbs, rudimentary marginal bulbs, e.g., Cirrhitiara superba, Aequorea macrodactyla), from those on which marginal tentacles will develop later on depending of the growth of the medusae (developing tentacular marginal bulbs, e.g., Malagazziidae).