Key to Class and Order of Australian Aquatic Flatworms

This key is apart of the Keys to Australian Aquatic Macro-Invertebrates.

The phylum Platyhelminthes (flatworms) is divided into three classes and a large number of orders and families.  The class Turbellaria contains free-living and commensal species, and the majority of aquatic flatworms are members of this class.  Classes Trematoda (= flukes) and Cestoda (= tapeworms), contain parasitic worms, but some Trematoda go through one or more free-living dispersive stages.  This key covers aquatic free-living turbellarians at family-group level, ectoparasitic trematodes (fish flukes, etc.) at order-level, and the final aquatic stage (cercaria) of the endoparasitic trematodes of some terrestrial vertebrates (family Fasciolidae: sheep liver fluke, etc.).  Other animals which could readily be mistaken for flatworms and are included in this key include Nemertea (ribbon worms), Hydridae (some Hydra-like Cnidaria), Tardigrada (tardigrades), and some families of segmented worms (Annelida).