In addition to their characteristics, in these cnidarians, there's the leap of the formation of a third layer of tissue during development, from the polyp state to certain jellyfish, such as some that belong to the taxon of hydromedusae.

除了它们的特征，在这刺胞动物之间，在发育过中，还有第三层组织形成的飞跃，从息肉状态到某水母，比属于水螅纲的水母。