"Worms" is a very broad term and doesn't refer to a single, specific group. There are many different types of worms, and they belong to various phyla, meaning they're quite diverse in their evolutionary history.

Here are some examples:

* Annelids: Earthworms, leeches, and marine worms like polychaetes belong to this phylum. They have segmented bodies.

* Nematodes: Roundworms are in this phylum. They are unsegmented and have a cylindrical body.

* Platyhelminthes: Flatworms, like tapeworms and flukes, belong here. They are flat and unsegmented.

* Nemerteans: Also called ribbon worms, these are unsegmented and often predatory.

So, to answer your question more specifically, you need to clarify what kind of worm you're interested in!