The correct answer is - worm's body.
In order for a living tissue to be fossilized, there need to be certain very specific condition that will enable its long term preservation. Also, the natural preservation types are relatively well suited for preserving the hard tissue, such as the bones, thus a beak, skull, teeth, is very probable that they can be fossilized under the right conditions. On the other hand, it is pretty much impossible that animals that are invertebrates, such as the worms, can be preserved. They do not have any hard parts on their body, only soft tissue, and once that decomposes there will be nothing left of the worm. The highest probability that are worm can be fossilized is through a print in some mud that was in a phase of hardening, thus giving us a mold of the worm.