This is the wheel spider of the Namib desert of southwest Africa. It's possibly the only animal other than man that employs a wheel in locomotion.
The spider digs a vertical burrow 16 to 20 inches deep on the, shallow slope of the dune and in the process is preyed upon by a wasp, which digs a parallel burrow to collapse the first. When the spider is exposed and can't fight off the wasp, it runs down the steep slope, folds up its legs into a wheel shape, and quickly rolls down the slope escaping the wasp, which usually loses track of the spider.
Although no other animal--except man, to my knowledge--applies a wheel in locomotion there are other organisms that do so. Various flagellated protists and bacteria use this technique in to propel themselves; what appears to be a wagging tail is actually a corkscrew-like apparatus rotating in a socket.
I'd be interested to hear of any other possible wheel-like structures employed in nature.