This is a f**king jellyfish.  It is the most evil life form in the universe.  If you see one, kill it on sight.  Good luck in doing so, you shall likely need it.

No loving god would create jellyfish.
They say eyes are the windows to the soul.  Jellyfish have no eyes.  This is not because they have no soul, but because their souls are so evil that one glance through a window into them would drive you into the furthest depths of madness for all time.
Jellyfish are not allowed in hell.  That would be too awful for the residents.
Many jellyfish are small and appear harmless.  This is only a ruse to fool you, for all the small Jellyfish take their orders from the larger ones, such as the one above, which is ten feet in diameter.
Jellyfish are damn near impossible to kill.  Only removing them from the water actually works.  On their territory, you are at their mercy, of which they have none.  Science has no word on the effects of crucifixes or holy water when doing battle with jellyfish, so don't bank on it.
Fact: Jellyfish do kill people.

This is a Giant Red Jellyfish.  It lives the deepest down in the ocean and is the most evil of all jellyfish.  It is the ruler of the vast empire of damnation that is the Jellyfish race, psychically transmitting its evil commands to the other jellyfish higher up.  It takes its own orders straight from the old ones, who have sent jellyfish to destroy humanity.  Just look at that bastard, doesn't it just scream "feeds on the souls of the forsaken"?

Remember the story of Pandora's box?  Yep, there were jellyfish in there.

This isn't me just making stuff up, either.  Jellyfish actually are sort of a menace.  They're currently destroying fish harvests in Japan, and are generally a bad, invasive species in any ecosystem they come in contact with.

Oh, and did I mention they actually are immortal?  Well, not all of them.  There's one species called the immortal jellyfish that does this weird thing where when it starts to get old it can somehow revert itself back into baby form, or "polyp" and start its life all over again.  And again.  Forever.  Science has said it is so.  The first ever of these guys from however many millions of years ago is still alive and out in the ocean somewhere.

I'm no scientist, but a combination of immortality and "devouring all our fish supplies" can only be some sort of apocalyptic survival movie waiting to happen(what world would be worth living in without tasty fish).  Unless we act now.  I'm not going to let a bunch of lovecraftian water horrors get in between me and my next plate of delicious tilapia.  And what of all the parts of the world where fish is the main diet staple that people depend upon?  Think of the children there.  Are you saying you want CHILDREN TO STARVE TO DEATH so that these f**kers can be protected?  Our choice is clear: The Jellyfish must be exterminated.

I move that the nations of the world join together against this common aquatic nightmare enemy.  As I said, the only way to kill them is to drag them up out of the water(if you try to kill one in the water, they release millions of offspring before they die, true story)  So, what we'll need is something like a fleet of fishing trollers to net as many of these bastards as possible and yank them out of the water.  It's our only hope.  And when we finally dry out the last of the abyssal terrors and humanity has one, we can come up with some awesome catchphrase for the film's hero played by Gary Oldman(why the hell not?) to say like, "Lookes like Earth will be having peanut butter, hold the jelly" okay so that was terrible, but you get the idea.  Fuck, If you people don't do something, I'll take down the floating doom balloons myself in a stolen legitimately purchased craft.  DEATH TO THE JELLYFISH!!!!!!!!!