Phylum Nematoda: The Roundworms

1. Phylum Nematoda:The Roundworms

3. Nematode = Thread? Roundworms got their name nematode because they resemble a thread. In Greek, �nematos� actually means thread About 20,000 described organisms

4. What is a Roundworm? Slender, unsegmented worms. Microscopic or up to a meter in length. Most are free-living inhabiting soil, salt flats, aquatic sediments, and water from polar to tropical regions. Parasitic Live in hosts almost every kind of plant and animal.

5. What is a Roundworm? The effects of nematode infestation on crops, domestic animals, and humans make this phylum one of the most important of all parasitic animal groups. Almost all species of vertebrates and many invertebrates serve as hosts for one or more types of parasitic nematodes.

6. Digestion Unlike the platyhelminthes, nematodes have a digestive tract with two openings. The body plan is called a �tube-within-a-tube.� The outer tube is the body wall and the inner tube is the digestive tract. Food moves in one direction through the digestive tract.

7. Form and Function in Roundworms Roundworms have specialized tissues and organ systems that carry out essential body function. In general, the body systems of free-living roundworms tend to be more complex than those of parasitic forms. Distinguishing characteristics of this phylum are their cylindrical shape, flexible nonliving cuticle, lack of motile cilia or flagella, and the muscles of their body wall run only longitudinally.

8. Body Covering Outer body covering is a thick, non-cellular cuticle secreted by the underlying epidermis, or hypodermis.

9. Feeding Most free-living roundworms are predators carnivores that use grasping mouthparts and spines to catch and eat other small animals. Some soil-dwelling and aquatic forms eat algae, fungi, or pieces of decaying matter. Other nematodes digest the bacteria and fungi that break down dead animals and plants.

10. Respiration, Circulation, and Excretion Like flatworms, roundworms exchange gases (respire) and excrete metabolic wastes like urea and ammonia through their body walls. (diffusion) They have no internal transport system.

11. Response Nematodes have simple nervous systems, consisting of several ganglia. Several nerves extend from ganglia in the head and run the length of the body. These nerves transmit sensory information and control movement. Roundworms have several types of sense organs.

12. Response A ring of nerve tissue and ganglia are found at the anterior end of their bodies. They have a pair of amphids more complex sense organs that open around their heads. They have a pair of phasmids similar in structure as amphids, but open around the posterior end of the body.

13. Movement Muscles of nematodes extend the length of their bodies. Together with the fluid in the pseudocoelom, create a �hydrostatic skeleton.� A hydrostatic skeleton is the use of coelom fluid to maintain the shape of the animal and allows for movement. Aquatic roundworms contract these muscles to move like snakes through the water. Soil-dwelling roundworms push their way through the soil by thrashing around.

14. Reproduction Roundworms reproduce sexually. They reproduce using internal fertilization. Female: has ovary, passes them to the uterus, where they are fertilized. Male: Sperm cells made in the testis and stored in the vas deferens. the male usually deposits sperm inside the female�s reproductive tract. Over 200,000 eggs can be deposited at once in the soil once they are fertilized.

15. Reproduction Cont. Parasitic nematodes often have complex life cycles that involve two or three different hosts or several organs within a host.

16. Anatomy

17. Classes of Nematoda Two main classes: Class Rhabditea � they are both free-living and parasitic forms. Class Enoplea � mostly free living, but includes some parasites.

18. Roundworms & Disease Many nematodes are very important pathogens of humans and domestic animals. Some of the nematodes we will discuss: Hookworms Trichina Worm Pinworms Filarial Worms

19. Trichina Worm They infect humans, hogs, rats, cats, and dogs. Hogs can become infected eating uncooked scraps of infected meat or rats. Heavy infections can cause death but lighter infections are more common. About 2.4% of the U.S. population is infected, mostly lightly.

21. Filarial Worms 8 species of filarial nematodes that infect humans. About 250 million people in tropical countries are infected with Wuchereria bancrofti or Brugia malayi, which live in the lymphatic system. They cause inflammation and blockage of the lymphatics. Females can be as long as 100 mm and can release live young, or tiny microfilariae into the blood and lymph.

22. Filarial Worms cont. Mosquitoes ingest the microfilariae when they feed. The worms develop to the infective stage while inside the mosquito and move into the mosquito bite wound when it feeds.

23. Filarial Worm Diseases Filarial worms cause three main diseases in their definitive hosts: Elephantiasis River blindness Dog heartworm

25. Hookworms Hookworms are so named because the anterior (head) end curves dorsally, resembling a hook. They have large plates in their mouths that cut into the intestines so that they can suck on the host�s blood.

26. Hookworms cont. Hookworms suck more blood than they can digest. A heavy infection can cause anemia. Eggs pass in feces and juveniles hatch in soil where they can live off of bacteria. If human skin comes in contact with the soil, infective juveniles burrow through the skin to blood. Bare foot, I think not!!!

27. Pinworms Pinworms are the most common worm parasite in the U.S., but causes little disease. It is estimated that 30% of children and 16% of adults in the U.S. have them. Adults live in the large intestine and cecum.

28. Pinworms cont. Females, about 12 mm in length, migrate to the anal region at night and lay eggs, causing itching. Scratching the anal region contaminates hands and bedclothes. So how do you test for something like this?

29. Scotch Tape Method Fecal examinations and finding the eggs, but eggs are often not found in feces. Many times the female pinworm will deposit her eggs on the skin around the anus. Doctors have started using the �scotch tape method.� Truth is in fact stranger than fiction.

30. Scotch Tape Method The scotch tape method consists of placing the sticky side of cellulose tape onto the anus overnight. The next morning the tape is umm...harvested and placed under a microscope to search for eggs. Drugs are effective against it, all members of the family should be treated at the same time because the worms spread easily through a household.

31. Pinworms Eggs develop rapidly and become infective within six hours at body temperature. When swallowed, these eggs hatch in the anterior end of the small intestine (the duodenum) and mature in the large intestine.