Laurie,
This is a great example of where TuFuse seems to shine -- masses of incoherent detail with no strong structure that would have obvious visibility errors. In other words, fine hairs and bristles. I'll bet it also turns out to be good for transparent subjects with overlapping details. There are a lot of those in microscopy, but that's a topic for a different forum. For insects, I suspect it'll do a great job with, say, a transparent wing having veins and hairs, in front of a detailed body.
About the transparent "jaw", I think what you're actually looking at is a drop of fluid. Notice that it's very asymmetric, left versus right, regarding where it meets the black part of the face. What the fluid might be, I don't know. It may have evaporated by now. If it hasn't, you might try touching it with some fine probe, like the end of a hair, to get a clue about the consistency. If it's thick like syrup but washes off with water, that would suggest something like partially dried nectar. If it's even thicker and won't wash off with water, it might be some sort of resin.
On the other hand, if it really is a jaw, then another stack from underneath to show it better would be most welcome!
I agree that your lighting tube is working great. Have you posted a picture of it yet, over in Technical? Words are great, but I'm not sure that what I'm envisioning is what you've actually built.
--Rik
