if this is the case is there any reason for my unborn to be humanoid?
can i get a ruling on this mugmug?
it will significantly change how my character looks.
As long as you aren't seeking any mechanical effect, such as found in the Floater or Many-Legged species feats, I generally don't care what you look like. However, it will be obvious to foes (in some fashion) that your appearance does not represent a mechanical difference.
For example, if you want to be legless but (mechanically) still be a walker, we can call it in this example some sort of ground effect fan that keeps you aloft. Therefore, you still have weight on the ground (for triggering traps), rely on the existence of the ground (for falling), can be tripped (fan temporarily snarled), etc. Basically, I'm willing to suspend a little disbelief.
The other option was to go with "lack of Floater or Many-Legged means you are bipedal," which may well be more reasonable than this approach.
[EDIT: Cleaned up my English; didn't change intent.]