Great
Galin, you can always be trusted to provide substance, if there is any. Since I don't own that particular book, would you mind trying to tell us how the picture looks like?
So it is pretty safe to say that Glaurung is a serpent-creature. Since serpent is a synonym for snake (as opposed to lizard, crocodile, dinosaur) I suppose that Glaurung indeed looked pretty much like I tried to describe in the op. Yet I've never seen him illustrated anything like how one must assume he looks like, given the texts and background material. On my HoME XI paperback, there he is on the cover, looking rather like a monstrous grub with a dental condition:
That's just awful (although I quite like the colours on the original).
On a google-search lots of other images pop up, but none showing a lithe serpent creature. Why is that, you think?