Turbellaria
Introduction to the biology of the freshwater Turbellaria, by S.M. Mandaville.

Marine Flatworms of the World
This site is mainly devoted to the Polyclads, an order of brightly-colored tropical platyhelminths. A long and detailed presentation of the Platyhelminthes, and hundreds of beautiful pictures of living specimens.

Turbellarian Platyhelminths Taxonomy
A hierarchical taxonomy of Platyhelminthes by Seth Tyler.

Dugesia
The anatomy of the turbellarian flatworm Dugesia tigrina, commonly known as planaria.