Acoelomates

Platyhelminthes and Nemertea - Details of the classes and subclasses contained in these two phyla, with photographs of certain example species.
www.emporia.edu/biosci/invert/lab3/

Reefkeeper’s Guide to Invertebrate Zoology: Flat and Ribbon Worms - Article outlining the biology of the Platyhelminthes and Nemertea.
www.reefs.org/library/aquarium_net/0297/0297_5.html