William Herkewitz at Popular Mechanics writes:

This miniature marvel is an adolescent issus, a kind of planthopper insect and one of the fastest accelerators in the animal kingdom. As a duo of researchers in the U.K. report today in the journal Science, the issus also the first living creature ever discovered to sport a functioning gear.

You have to go to Popular Mechanics to get a look at the "scanning electron micrograph image" of the gear. It's kind of wonderful.