Hmmm...looks like an emergency queen cell.
When I started my observation hive, it forced them to start several of them. Some of them were so small that you could barely tell they were there, looked like an oblong capped worker cell. I had several "interesting" queens hatch out, a really tiny one, a ragged one, and one that eventually survived and mated and has a decent laying pattern, although not much area to lay in yet.
Rick