Biology/Natural History: This is the largest of our local Hydrozoan jellyfish, though the Scyphozoan jellyfish can grow much larger. Feeds mainly on gelatinous plankton such as Mitrocomella polydiademata and other hydromedusae, on ctenophores, on polychaetes, and on appendicularians. It may occasionally be cannibalistic. Also eat larval fish such as Pacific herring, Clupea pallasi. This species is bioluminescent and may flash brightly when disturbed. A related species off Baja California can divide by fission. The hydroid stage of this polyp is not often seen in the field. Some references suggest that the polyps may be what is now identified as Campanulina forskali. Aequorea victoria is the source for "green fluorescent protein", which is a marker used in molecular biology.