In the post before your last post, I said they do have a back and that Google explained it. Google is a website where you can discover new things, you may wanna try it out. "Worms do not have a backbone (they are invertebrates), but they do have a distinct "back" (dorsal side) and "belly" (ventral side), as well as a front (anterior) and back (posterior) end. Their bodies are segmented tubes with a dark-colored dorsal surface and a lighter, flatter ventral surface."
Invertebrates. No back. Read a book not the internet