Segmented worms, also known as annelids, do have a more complex nervous system compared to the other types of worms listed. While flatworms, roundworms (nematodes), and segmented worms (annelids) all have nervous systems that can be considered simple, annelids possess a more developed nervous system with a ventral nerve cord and ganglia.
To clarify each type briefly:
- Flatworms (Platyhelminthes): Have a simple nervous system without a central nervous system; they possess a pair of cerebral ganglia and longitudinal nerve cords.
- Roundworms (Nematodes): Have a simple nervous system with a nerve ring and longitudinal nerves.
- Segmented worms (Annelids): Have a more complex structure, including a ventral nerve cord and segmental ganglia, making their nervous system more developed compared to flatworms and roundworms.
So, the answer is Annelids (Segmented worms), as they do not have a simple nervous system compared to flatworms and roundworms.