An unsegmented, bilaterally symmetrical, soft-bodied invertebrate with a flattened body, hence the name, belonging to the phylum Platyhelminthes. Flatworms lack a body cavity (coelom), specialized organs for circulation or respiration, and an anus. Nutrients and oxygen diffuse through them. Most are hermaphrodites. There are many thousand species, some parasites, e.g. tapeworms and flukes, or pests, e.g. the New Zealand (Arthurdendyus triangulatus) and Australian (Australoplana sanguinea) flatworms which prey on European earthworms.