When you mention cranefly larvae, most people will think of the leatherjacket found under lawns eating grass roots, but there are a number of aquatic species too. The thing that surprised me about this larva was those large mouthparts, which unsurprisingly show it is predatory.
They are an indicator of clean streams and rivers , so finding one was good news for this stream, which was also full of other good water quality bioindicators like stonefly larvae and clinging mayfly larva. The 2 black dots at the rear end are breathing tubes, which have gills around them to extract oxygen when underwater.
Another new aquatic species for me too!
Oldham, John N., 1926, On the larval stage of Pedicia rivosa L. Proc Roy Physical Soc : 33-53
Iowa State University Entomology., 2013, Genus Pedicia, http://bugguide.net/node/view/14194