Dead worm mob

I remember hearing one of the devs talking about how they were play testing with a worm mob that would be very big and long. I think because of how big the caves are that they could use a bigger mob lurking in there. These bone worms would be worms that are just made out of bone blocks. You could not kill them but if you can somehow hit it, it would leave behind a bone with out you harming the worm.