Parasites

Many ectoparasites have developed structures, such as suckers, hooks, and teeth, which help penetrate the host's outer surface. Freezing is not likely to be severe enough in the field to kill a significant number of cysts. Parasitic worms, like flatworm and roundworm, usually live in the intestines, lungs, liver, or othre internal organs of their hosts. Cool, moist conditions are most favourable for survival. For example, when invaded by a parasite, a host often triggers an immune response, a cellular reaction that works to destroy the invader. They don't need to see, hear, smell, or move if they live in a nutrient bath in the host's intestine and don't need to seek or capture food.

Parasites that live on the inside of the host's body are known as endoparasites and outside of body called ectoparasites. These worms have developed adaptations that enable them to avoid the host's immune response, such as during a developmental stage when they are protected by a cyst wall or an outer surface thta constantly changes, thereby making it difficult for the host immune system to target the parasite for attack. This distinction reflects adaptations made by the parasite to overcome certain barriers t parasitism. They even lack a digestive system and circulatory system. They don't require digestive or circulatory systems becuase their cells are in close contact with already digested food, water, and gases. Tapeworms do not have eyes, ears, noses, or appendages.