I want to know the answer to the following question:
A name for a group of primitive flatworms is what?
All the background I'm provided with is that "It has not been definitively established whether the existence of these brainless species indicates that the earliest bilaterians lacked a brain, or whether their ancestors evolved in a way that led to the disappearance of a previously existing brain structure.". Is that enough to answer the question?
Answer: no