Megaphobelma Robustum

The area in question isn't even visible in this molt. You need to unwrap the abdomen.

@03ISA Putting the abdomen in water with a drop of dish soap (to reduce surface tension) for a few minutes makes it easier to unfold.

I would also cut off the parts you don't need, so you just have the inside of the abdomen between the book lungs. Otherwise, it tends to fold in on itself.