Examples

phylum Platyhelminthes
Class Trubellaria
- Free-living flatworms
- Less than 1 centimeter in length
- Found in moist tropical areas
- Freshwater planarian (Dudesia)

Class Trematoda
- Also known as flukes
- Some are external parasitic flatworms that live on the skin, mouth, gills of a host
- Many are internal parasites that infect the blood and organs of humans.
- Although flukes are small, they can damage their host greatly during their life cycle.

*Blood flukes, genus Schistosoma, live within the blood vessels of the intestines that are parasitic to hosts. Most flukes are hermaphrodites and undergo sexual reproduction. Flukes produce more than 10,000 eggs and fluke eggs are not digested by the host and become part of the feces. Eggs are hatched as they get into the water. Soon the larvae burrow inside specific snails where the flukes are reproduced asexually.

* People who are infected by fluke often get sick and die as their immune systems are weakened by fluke. “Swimmers itch” is also caused by flukes living in freshwater. However, because the worms do not detect humans as their hosts, the itch goes away after a time and the bodies repair the damages.

Class Cestoda
- long, flat parasitic worms
- Also know as tapeworm

* These members have a head called a scolex on which a ring of hooks are attached. The structure help worms to attach to intestine where worms absorb food that is already digested by their hosts.

* Proglottids or sections are formed behind the scolex of the tapeworm. Proglottids make up the body of the tapeworm. Proglottids are located at the anterior region of the young tape worms, and mature tapeworms have proglottids at the posterior region of the tapeworms.

* If food or water that is contaminated with tapeworm eggs is eaten by cows, pigs, or other hosts, the eggs enter the bodies of hosts and hatch into larvae. These larvae burrow into the muscle tissue of the host and form a dormant protective stage called cysts. Once the larvae become active, it absorbs food, hanging on the intestinal wall.

phylum Nematoda
Ascaris
- Parasitic roundworm lives in human bodies
- Known as ascarid
Ascarids live in the intestines, where they produce hundreds of eggs. The eggs eventually leave the body in the feces. Eggs hatch into larvae when they enter other hosts’ intestines. The young worms burrow into the walls of the intestines and enter blood vessels. They travel to the lungs and climb up into the throat where they are swallowed. Worms are carried back into the intestines again and repeat the cycle.