Even in a habitat — the ocean — that is known for its otherworldly creatures, jellyfish and sea jellies are in a class of their own. The fascination begins with their unique physiology (that's the way in which their body is built and functions).
Their bell-shaped bodies are up to 98 percent water and lack a brain.
Many species can glow.
Others have stingers that carry some of the deadliest toxins on the planet.
And they have a complex life cycle that sees them going from rooted on the seabed like plants into independent adults wandering the seas.
A great majority of jellyfish are small to moderate in size. The barrel jellyfish is often one of those moderate ones. It can reach around 40 cm (16 in) in width with tentacles of about 1 m (3 feet) in length — think of a large frisbee with some dish towels trailing behind and you get the idea.
But a human-sized jellyfish recently spotted off the coast of Cornwall, Britain, proved that they can grow much larger.
Barrel of, uh, fun?
So what do you do when you encounter a human-sized jellyfish? You pretty much just try to keep your distance and watch it do its thing.
Thankfully, this jellyfish's sting is too weak to harm humans, so the divers in this video were never in danger from it. The divers (biologist Lizzie Daly and underwater cinematographer Dan Abbott) observed the creature for about an hour. They released their footage as a part of Wild Ocean Week, to raise awareness of wildlife in the waters around Britain.
Well, Lizzie and Dan, you can definitely consider us aware now. Not sure if we're ready to jump in the waters right after you, but we can certainly appreciate the unique majesty of this jellyfish.
See it for yourself in the video below!