It's obviously something living. It seems to be attracted to, or interacting with, the submersible. If I'm reading that screen right, it's over 5,000 feet down. I've watched the video three times, and can't get enough. What was that deep sea horror movie with the angel/jelly looking aliens? The one where their ship was in the deep trench...? It looks like an brown version of one of those aliens. Thanks for posting OP!