Predatory mite

Update: someone just told me this is a mite of the genus Anystis, a genus of generalist predatory mites.

Thanks :) @Leuba: No phoresis going on here, I don't think. I know mites do that, but in this case, the prey wasn't moving (or at least, not walking: might have still been alive), and the mite was standing on the leaf and holding it, with mouthparts in contact with the prey. I've seen these mites running actively all over the leaves of the plant where I found it, so I'm pretty sure they are a predatory species :)