One quirk of the box jellyfish is that they have eyes. These eyes aren't quite like ours, but they are more advanced than you would think.
It is not understood how box jellyfish have eyes, and yet they have no brain. They don't have anything to process or make sense of the images they are receiving. In fact, scientists questioned whether or not these eyes were even functional for some time. But recent tests have suggested they do in fact work. These tests include setting poles of various colors and transparencies into a tank of box jellyfish. In tanks with clear or light colored poles, the jellyfish ran strait into them. In tanks with black, solid colored poles, the jellyfish actually avoided them! This really brings out the mystery of how these jellyfish work. Perhaps they are smarter than we think!
The reason I bring this up is because a small box jelly medusa was created a few days ago, in one of my polyp cultures of Carybdea rastoni. I decided to examine this one under a microscope. From there, I was able to really examine these eye structures. The jellyfish happened to be positioned so these eyes were "looking" right up at me. Shivers went up my back, even though I doubt it will be greeting me any time soon.
Above are two photos of the box jelly. The first is an overall shot of the jelly. At the time, it was a little balled up. The bottom of it is facing up, though. The second image is a close up of the eye structure.