The type of worms that are primarily parasitic are flatworms and roundworms.
- Flatworms (Phylum Platyhelminthes) include many parasitic species, such as tapeworms and flukes.
- Roundworms (Phylum Nematoda) also include many parasitic species, such as hookworms and Ascaris.
While some species of annelids and segmented worms can have parasitic lifestyles (like certain types of leeches), flatworms and roundworms are more traditionally associated with parasitism.