How is the adaptation to the parasitic lifestyle of the roundworm expressed?

Modification of the mouthparts and digestive enzymes – the use of food, blood, or tissue from the host.
The reduction of unnecessary sense organs and locomotor organs in the adult stage is not required, since they live in protected, optimal conditions.
Specialized reproductive strategies – may have male and female reproductive systems; can reproduce asexually; can produce large numbers of eggs / larvae.
Resistance to attack by the immune system – there are antigens adapted to the host’s organism (the host recognizes the parasite as its own tissue); changes its own antigens.