It vaguely reminds me of the stuff you would see when you peel a layer of blue-green 'algae' off of a plant leaf or other surface. Except that stuff was white, and essentially (i think) just dead algae tissue. This, also, I'm thinking is 'dead' -- offal of some sort. Either way its pretty gross looking, I'd vacuum the heck out of it and check ferts/co2 levels.