This almost mely*rid-looking (to me anyway) larva was the only one of its kind I encountered while stripping bark from a 2-3-year-dead red oak I toppled. It was one of several unknown subcortical larva types I discovered inhabiting this tree. Unless I overlooked the larva I'm thinking of, this little guy was another one-and-a-half millimeters longer, trailing a fleshy caboose that vanished before I got around to shooting my specimens.
Okay, I now think this is a larval scraptiid. I've just revisited images I took of one in New Mexico and the morphology is very similar, including the fleshy caboose:
In a comment on that page Kieth Bayless says scraptiid larvae are very rare in collections and that they lose their "caboose" just prior to pupating. That means this little guy may actually be a pupa as I type this. I'll check in a few minutes :-)