Morphological Adaptations:
Body Covering: Thick tegument, frequently provided with scales. Possibly continuously renewed by mesenchymal cells.
Adhesion: Suckers, hooks and spines.
Locomotion: Locomotory structures like Cilia are absent in adult, but present in the free living larval forms.
Trophic Organs: Elaborate organs for nutrition are not needed as the food of parasite comprises digested and semi-digested food. Alimentary canal has partially or completely degenerated in Platyhelminthes.
Nervous System: Reduction of nervous system and near total absence of sense organs, as response to stimuli is not of much importance.
Reproductive System: Highly evolved to meet the need for tremendous egg production. Many Platyhelminthes are Hermaphrodites, because it ensures that copulation takes place even when very few individuals are present. Uterus size is maximised at expense of other organs in the body to accommodate eggs.
Physiological Adaptations:
Protective Mechanism: Alimentary canal of parasites must protect itself from digestive juices of the host. Stimulate walls of gut to secret mucus which forms a protective covering around the parasite. Secrete anti-enzymes that neutralise digestive enzymes. Continually renew their protective body covering.
Anaerobic Respiration: Respire anaerobically by breaking down Glycogen. Environment in gut and bile ducts is devoid of oxygen.
Osmoregulation: In intestinal tapeworms, osmotic pressure adjustments permits absorption of host’s digested food.
High Fertility: Because the parasites have a complicated life cycle across multiple intermediate hosts, chances of survival are generally low. This is countered by producing millions of eggs.