Ah, the beauty of nature never ceases to amaze me.
I once thought that all ultimately symbiotic relationships first emerged as parasitic ones in the earliest annals of organic history, for what else but the predator-prey relationship could bring two disparate species into such intimate contact?
Lichens are also a good example of this, since they exist as a symbiosis between an algae and a fungus in which the fungus provides structure and protection while the algae provides energy through photosynthesis. The trick is though, that the fungus is actually eating the algae, but not quickly enough to inhibit the overall growth of the symbiotic organism.
I don't know where I stand on this view right now, but it appeals to me to think of such necessary and vital cooperation among different species as the historical result of an inversion of the old predator-prey duality.
This critter, though, while being exceptionally fun (its "face" looks like an opera mask!) is also the most bizarre example of this that I have been able to find.
Please, read, learn, and enjoy its strangeness at Wikipedia: