Possibly a decade ago I read an article that described worms as basically being akin to one long nerve. It was impactful enough that I stopped hooking worms for fishing ... before I eventually gave up that "sport". It never ceases to amaze me that biologist pursue the study of pain in other animals and seem surprised to confirm its existence. Of course, they have a vested interest in not finding proof of experiencing pain as it would make their experimentation seem cruel. Which it is. Biology, lacking any first principles, is not a science. Biology is at best butterfly collecting unceasingly surprised at everything because it cannot predict anything.