This includes liverflukes, flat worms (planarians), tape worms etc.; neither the vascular nor the respiratory system is present; the excretory system end in characteristic flame cells; digestive system is incomplete with a mouth but without anus; nervous system comprises of a nerve ring, nerve ganglia and nerve cords; reproductive system is well developed and both the male and female organs are present in the same individual. Some are free living, others are parasitic, the latter pass through several intermediate development stages and live in the bodies of other animals during their life-history.
Liverflukes are parasitic and found in the liver and bile ducts of sheep, cattle etc, and occasionally in men, producing disease called 'liver rot'. Tape worms are parasitic in the digestive tracts of vertebrate animals, including men. They are long, flat, ribbon-like worms.