The Lions Mane Jellyfish is the largest jellyfish in the world. They have been swimming in arctic waters since before dinosaurs (over 650 million years ago) and are among some of the oldest surviving species in the world.
I’m going to cry
The largest Lions Mane found was only about 7 1/2 feet (the bell, though the tentacles reached 120ft) so this picture is super misleading. You can see a person compared to a life size model on the wiki page.