At this point, we're kinda used to the idea that the ocean's home to some truly crazy stuff -- like leaping ninja octopi, for example. The craziness just ramps up as you go further and further into the murky depths, to the point where you'll run into the kinds of creatures you'd expect to find on Star Trek (no, not Brent Spiner). Case in point: this humongous, extraterrestrial-looking jellyfish.
If this thing doesn't trigger your Thalassophobia (fear of the sea), nothing will. It's called Stygiomedusa Gigantea, and it's actually pretty rare -- as in, it's only been seen around 100 times in the past 100 years. The head portion of its body can measure up to 3ft in diameter, while its flowing tendrils can grow to 20ft in length. Pretty hard to imagine this thing coiling itself around your leg and dragging you down to never see the sun again, right? Definitely not nightmarish at all.