Straxus, great question -- it's something I've been wondering about too, since I've done a number of Gand customs, and have attempted some without masks. (And I would love to see yours, too.
Whatever mask or helmet Zuckuss is wearing, it seems to (a) have many of the same organic looking creases, etc. as he does (which seems funny for a helmet) and/or (b) be the same color as he is. I've always considered that the bit around his neck with the tubes and the black & silver bit of the mask over his mouth are certainly artificial, but it's never been clear how much else is natural and how much not.
Interestingly, the new bust by Gentle Giant almost
seems to clarify this issue. In this piece, it looks as though the mask goes over his eyes & includes goggles, too -- that are the same color as his chitin & with somewhat similar contours -- but doesn't cover the top of his head. At least that I thought -- here's a photo:
So that curved sort of brown flap right left of his eye could be interpreted the edge of a mask that covers his eyes and mouth and matches his natural coloring. Just a thought.
Much of it has to do with the question: other than respiratory equipment, how much protetction do Gands really need in an oxygenous atmosphere? Does the oxygen get in between their chitin plates and itch, for example? Would it do so on the head? There are several RPG stats, etc., on their heavy natural armor, even on the fact that their eyes are armored. So it seems that even a partial mask could well be superfluous -- in which case maybe just the breathing mask and "collar" are the artificial bits. Personally, I like having as much as possible be natural!
Incidentally, just for fun, here's a neat sort of hypothetical "anatomical drawing" of a breathing Gand which my friend Beedo Sookcool made some years back when we were discussing these issues with regard to a fanfic of mine on Zuckuss's early years that is still in progress. He calls it "The Visible Gand."
(Either that, or "Zuck nekkid."
... the Findswoman