I did a lot of examination of the episode when I was working on my "proof of concept" Doomsday Machine VFX re-do...
The closest I can come to explaining what the filming model is...
Yes, some kind of wire armature to support the thing. They only shot it from one side... it does move in one shot... so it was something that existed in three dimensions...
Over the wire, it looks like heavy, gaffer's strength aluminum foil used for blocking light on the set... this is wrapped around the armature, and forms the major sections... it is unpainted and still reflects light.
THEN...
it looks to me as if another item from the gaffer/lighting kit is used... some blue gel plastic material... the kind used to change the color temperature of lights. it seems to me that this is wrapped over the outside of the foil. If you look closely at the stills, you can see the faint outlines of what looks to be adhesive tape just holding it together. The gel plastic is then folded over the lip of the maw in sections and secured inside... where the foil is bare.
It seems that there is a light source inside... it is possible they built this assembly over an existing studio light... maybe a small fresnel light to provide the illumination from within. It would also explain why they used foil and wire... heat resistant, as was the lighting gel.
As to the lighting effect seen in the show... I believe this was a bit of trickery as well. They projected the moire pattern behind a still of the miniature, with the light source cut out... so the moire would appear on the inside of the "doughnut" shape... but still revealing the foil reflecting the studio light.
What do you guys think? It would also explain the somewhat transparent property of the model in the side shot, as we are seeing through the gel material, and where the foil doesn't cover, we see the opposite side of the maw.
That's my two cents.
drd