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I would have been tempted to see if it'll brush off. (I.e. as in 1 or 2 extremely gentle strokes max with a dampened small paintbrush). If it's been on there for a while though, it's probably dried on, so not worth poking about. When it moults it'll be still be attached to the moult, so your t will be rid of it. If I were you, I would take the moult out as soon as possible and then you can have a proper look at what it was.
The enclosure looks a bit too wet though. Let it dry out, and from then on just overflow the waterdish so there is a dry area and a slightly damp area.