Some say they are monophyletic; that is, they have a common arthropodal ancestor. Some say they are polyphyletic, evolving from different creatures, maybe worms. Some say insects evolved from crustaceans. Some say they’re more closely related to centipedes. Where can we place the trilobites? What about the anomalocarid discovered in Ogygopsis Shale? Multiple evolutionary processes cloud the waters. Features may be lost and re-evolve. Similarities might have resulted from convergent evolution. Maybe they evolved from an animal that molted.