The Lions Mane Jellyfish is the largest jellyfish in the world. They have been swimming in arctic waters since before the dinosaurs (over 650 million years ago) and are among some of the oldest surviving species in the world.The largest can come in at about 6 meters and has tentacles over 50 meters long. Pretty amazing when you think these things have been swimming around for so long.They have hundreds of poisonous tentacles that it used to catch passing by fish. it then slowly drags in it’s prey and eats it. Lion’s mane jellyfish remain mostly very near the surface at no more than 20 m depth, their slow pulsations weakly driving them forwards; they depend on ocean currents whereby the jellies travel great distances. The jellyfish are most often spotted during the late summer and autumn, when they have grown to a large size and the currents begin to sweep them closer to shore.On July 21, 2010, around 150 people are thought to have been stung by the remains of a lion’s mane jellyfish that had broken up into countless pieces in the United States. Considering the size of the species, it is possible that this mass incident was caused by a single specimen.