Jellyfish several countries; jellyfish caused a cascading blackout in the Philippines in 1999, as well as damaging the Diablo Canyon Power Plant in California in 2008. They can stop desalination plants and ships' engines. Jellyfish Jellyfish or sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are not mobile, being anchored to the seabed by stalks. The bell can pulsate to provide propulsion and highly efficient locomotion. The tentacles
Jellyfish They remain in still waters until the tide rises, ascending and allowing it to sweep them back into the bay. They also actively avoid fresh water from mountain snowmelt, diving until they find enough salt. Jellyfish are hosts to a wide variety of parasitic organisms. They act as intermediate hosts of endoparasitic helminths, with the infection being transferred to the definitive host fish after predation. Some digenean trematodes, especially species in the family Lepocreadiidae, use jellyfish as their second intermediate hosts. Fish become infected by the trematodes when they feed on infected jellyfish. Fisheries have begun harvesting the American cannonball