[spoiler]Oops, I thought you were talking about the eyes. My bad.
Yes, it looks natural to me. Just because something doesn't happen here on Earth is the worst reason in the universe for something not happening on another planet. I mean, seriously. I recall a story that the best candidate for life on Mars (at the time) was rejected on that ground that it resembled nothing like life on Earth (it was later proven to be an artifact of the methods used for examining the object). The moral of the story is that you must throw out all preconceptions about what is possible and what is not before you dive into exobiology.
That aside, the structure looks remarkably like the stirrup bone in the human inner ear, just without the base. The stirrup bone also has a hole in the middle, half of the bone is roughly square (more square than the eyestalk!) and is much tinier. There are other square-ish bones in your body, too. Some of them are even relatively cuboid in shape. They're called molar teeth. I can think of bones with holes in them - the major one is called a skull, and is full-on hollow![/spoiler]