Make a conclusion about the reasons for the appearance of the structural features of parasitic worms.

The roundworm (roundworm) has three lips with suction cups. This structure of the mouth allows them to keep in the walls of an intestinal attack. Bovine tapeworm (tapeworm) has a head with hooks that hold it in the intestinal wall. He also lacks a digestive system. The liver fluke (flatworm) also has special suction cups. At the same time, all worms have a special mucus that prevents their digestion.