The ranks used to be secret, so that getting a new one was more exciting, or special. But they were published some time ago in that thread happyguy936 posted.
The ranks are periodically changed, usually when a new Oddworld game comes out. So as to have the ranks updated with current and new Oddworld creatures.
And actually, if Xavier weren't a Moderator we'd have to create a new rank just for him! As he has over 7000 posts
Alcar...