While looking through the slug/snail tub that has been overrun by babies, I noticed this little fellow:
My apologies for the poor quality of the picture, but it still makes the point. This little Deroceras baby is merely half a slug! His body stops at his mantle. It doesn't appear to be doing him any harm aside from making him comically short, nor do the others seem to be rejecting him. He behaves just like a normal slug. He's as cute as a freaking button and I truly hope he grows up. I have a few stubby slugs of L. valentiana, but nothing like this little guy.
Due to the short lifespan and quick generations of Deroceras, I figured I'd see some mutations, but I never expected anything like this.