Flatworms consist of a dorso-ventrally flattened body organisms.
Roundworms consist of generally rounded and unsegmented organisms.
Example: Tapeworm.
Example: Roundworms (Ascaris).
The main difference between flatworms and roundworms is that flatworms consist of a dorso-ventrally flattened body
whereas roundworms consist of a cylindrical body tapered to a fine point at each end.