 It is placed at order rank in many older classifications, and limited to contain the Narcomedusae and Trachymedusae.But the Actinulidae, then considered an independent order, and probably also the Limnomedusae which were traditionally placed in the paraphyletic "Hydroida", belong to this group too.It is not entirely clear whether the Limnomedusae and the Trachymedusae as conventionally circumscribed are monophyletic

The freshwater jelly "Craspedacusta sowerbyi" is a well-known member of the Limnomedusae and might thus belong here.