Heaviest jellyfish

Because they are so gelatinous and insubstantial, composed almost entirely of water and soft parts only, it is not readily possible to obtain accurate weights for jellyfishes. However, based upon its exceptional body size, volume and combined tentacle mass, the lion's mane jellyfish Cyanea capillata, currently the record holder for largest jellyfish, has been estimated to have a maximum weight exceeding 1 tonne, making it by far the heaviest jellyfish species. It has a global distribution in open oceans, but is found mainly in the North Atlantic, North Pacific and North Sea, as well as around Australia in the South.

Named after its mass of tentacles being fancifully likened to the mane of a lion, this gigantic species is bioluminescent, and is known to feed, cannibalistically, upon other, smaller jellyfishes, as well as upon small fishes and zooplankton, putting to good use the many stinging cells or nematocysts present upon its numerous, exceedingly long tentacles, which it trails down through the water below its bell like a stinging curtain of death in which to ensnare and fatally disarm its unsuspecting prey victims.