Platyhelminthes- Arizona's Tree of Life Web Page. Pictures, characteristics, phylogenetic relationships, references on flatworms. A picture of a flatworm, and a link to trematodes (aspidogastreans).
Flukes- Information and links to other pages on specific species.
National Center for Infectious Diseases- This CDC site has many links to information on bacterial, viral, protozoan, and worm-related diseases (primarily affecting humans).