What is a common ancestor to the flatworm?

Flatworms, belonging to the phylum Platyhelminthes, are believed to have a common ancestor that was a simple, bilaterally symmetrical organism resembling acoelomates. This ancestor likely lived in aquatic environments and had a basic body plan with a centralized nervous system. Molecular studies suggest that flatworms share a lineage with other protostomes, linking them to a broader evolutionary history that includes various invertebrate groups.