What was Shelob, and more importantly, what was Ungoliant?

[Legate of Amon Lanc]

An interesting idea with Tom Bombadil, but I always considered Ungoliant a Maia and nothing I saw this far opposes it. The Silmarillion says:

Originally Posted by Chapter 8; Of the Darkening of Valinor

The Eldar knew not whence she came; but some have said that in ages long before she descended from the darkness that lies about Arda, when Melkor first looked down in envy upon the Kingdom of Manwë, and that in the beginning she was one of those that he corrupted to his service.

"And that in the beginning she was one of those that he corrupted to his service" to me creates associations with the Maiar who were swayed by Melkor to join him. To me, this is clear enough. It is true she could have been otherwise, but everything speaks for that she was an Ainu. On what evidence do you base your opinon that she was not an Ainu?

And by the way, are you sure he was riding her? Did she not just accompany him?