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Learn about the characteristics, feeding habits, reproduction, and parasitic nature of unsegmented worms, including flatworms (Platyhelminthes) and roundworms (Nematoda).
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1.Part One – Unsegmented Worms • Their bodies are not divided into specialized segments. • There are two phyla: • Platyhelminthes are the flatworms • Nematoda are the roundworms
2. Phylum Platyhelminthes They are the simplest animal with bilateral symmetry. Most members have enough cephalization to have what we can call a head.
3.They are usually only a few millimeters thick but can be several meters long. • Flatworms feed in two different ways. Some may be carnivores or scavengers, others are parasites.
4.The carnivores and scavengers are free swimming in streams, lakes, and oceans. They feed on tiny aquatic animals or dead aminals.
5.They have a mouth leading to a pharynx which is used to suck food into the gastrovascular cavity.
6.They have intestines where the food is broken down by enzymes and absorbed by diffusion into the tissues.
7.Parasitic flatworms feed on the blood, body fluids, and tissue of their host. • Most have a more simple digestive tract than free living flatworms.
8. Tapeworms are flatworms that live inside the intestines of their host. They have no digestive tract at all. They have hooks that attach to the intestine and take food that has already been digested by the host.
9. Flatworms do not have much in the way of circulatory and respiratory systems. Because they are so flat they can diffusion to transport nutrients and oxygen to their tissues.
10. They can also remove their waste by diffusion. • Flatworms that live in freshwater have special cells called flame cells they can use to remove excess water from their bodies.
11. Flatworms have a nervous system with a distinct head and a simple brain. They have long nerve cords that run down the length of the body and short cords that run across it.
12. Many flatworms have one or more pairs of light sensitive organs called ocelli or eyespots. They cannot form images.
13.They also have chemoreceptors that can detect chemicals in the water and locate food. • Most parasitic flatworms do not have nervous systems because they do not need one.
15. Flatworms get around by using the cilia on the ventral side to help them glide around AND they have muscles they can use to swim.
16. Flatworms can reproduce both sexually and asexually. Most free living flatworms are dioecious but do not self fertilize. They lay the eggs in small clutches.
17. Asexual reproduction can occur by fission or the worm may simply fall to pieces. Each piece will grow into a new worm.
18. Most free living flatworms belong to the class Turbellaria. Most are less than 1 centimeter in length but in the tropics they can reach lengths of 60 centimeters.
19. Members of the class Trematoda include the flukes. Most are internal parasites that infect the blood and organs of their hosts.
20. Class Cestoda includes the parasitic tapeworms. • They have a head called a scolex that have several suckers and a ring of hooks that are used to attach to the intestine of the host.
21. They are almost never fatal but they can make the host very sick and weak. • The body is divided into regions called proglottids. The ones closest to the head are small, the posterior ones are large and full of eggs.
22. When they become mature they break off and are passed out with the feces. A single proglottid may contain over 100,000 eggs. A single worm can make over half a billion eggs each year.
23. The Phylum Nematoda are known are roundworms. • They are the simplest animals to have a digestive system with two openings ( a mouth and an anus). • They range in size from microscopic to a meter.
24. They are just about everywhere. A bucket of soil may contain more than a million. • Most are free living but many are parasitic. • Free living roundworms are often carnivores.
25. They breathe and excrete their waste through the body wall by diffusion. • They have a simple nervous system consisting of several ganglia (groups of nerve cells) in the head region. They also have several sense organs used to detect chemicals.
26. Roundworms reproduce sexually. Most species have males and females but some are hermaphroditic (both sexes on the same individual). • Fertilization is internal (happens inside the body).
27. Ascaris is the parasitic roundworm that infects humans. The adult worm lives in the intestine where it produces eggs that leave the body in the feces. If food or water that is contaminated with the feces is eaten by another host the eggs hatch in their intestine.
28. The young worms burrow into the walls of the intestine and enter the blood stream. They are carried around in the blood until they end up in the lungs.
29. Here they break out into the air passages and climb up into the throat where they are swallowed and carried back into the intestine where the cycle start all over again.
30.Other parasitic roundworms: • Hookworm • Trichinella • Filarial worms • Eye worms
31. Hookworms are common human parasites in the southeast. • ¼ of all the people in the world are infected with a hookworm. The eggs hatch outside the body and develop in the soil.
32. They will burrow through the skin of an unprotected foot and enter the blood stream. • From the blood they enter the lungs and …
33. Trichinella cause the disease trichinosis.They live and mate in the intestine of the host. The female with the fertilized eggs release the larva into the bloodstream. They then leave the bloodstream and burrow into organs and tissues.
34. The larva form cycts in the hosts muscle tissue which are very painful. • Humans get the disease by eating infected pork that has not been thoroughly cooked.
35. Filarial worms are found mainly in the tropics. They live in the blood and lymph vessels. They are usually transmitted by the bite of a mosquito.
36. The infected persons blood and lymph vessels can become clogged with the worms. This causes swelling in that part of the body.
37. Eye worms are closely related to filarial worms and are found in Africa. They affect both humans and baboons. The worms enter the blood stream and occasionally move across the surface of the eye. That’s how they get the name.
