Jellyfish most are nowhere near that large). They have a moderately painful, but rarely fatal, sting. The increasingly common giant Nomura's jellyfish, "Nemopilema nomurai", found in some, but not all years in the waters of Japan, Korea and China in summer and autumn is another candidate for "largest jellyfish", in terms of diameter and weight, since the largest Nomura's jellyfish in late autumn can reach in bell (body) diameter and about in weight, with average specimens frequently reaching in bell diameter and about in weight. The large bell mass of the giant Nomura's jellyfish can dwarf a diver and is nearly
Helmet jellyfish Helmet jellyfish The helmet jellyfish ("Periphylla periphylla") is a luminescent, red-colored jellyfish of the deep sea, belonging to the order Coronatae of the phylum Cnidaria. It is the only species in the monotypic genus "Periphylla." "P. periphylla" represents an exception, very rarely found in the phylum "Cnidaria": the medusae do not go through a polyp stage, thus presenting a "holopelagic" life cycle. The medusae strew fertilized eggs in open water and these develop directly into medusae, whose development rests entirely upon the egg's high yolk supply. The ephyra stage common among other jellyfish is not observed in "P. periphylla". The