2. Phylum Nematoda The Roundworms “thread” “like” www.onacd.ca

3. Identifying Characteristics of Nematodes Pseudocoelomate which allows them to have a complete ONE WAY digestive tube (separate mouth and anus but no muscles!) Exhibit cephalization with a ventral nerve cord No respiratory or circulatory system present Developed reproductive system and excrete wastes through a pore Sexes are separate (dioecious) and use sexual reproduction Bodies are unsegmented and they are born with a certain number of cells that increase in size as they grow Their epidermis secretes a cuticle made of collagen to keep it from drying out and this cuticle molts as the worm grows Possess only longitudinal muscles Contains many parasitic and free-living forms found in fertile soil

4. Parasitic Species of Nematodes include: WHIPWORMS which invade the human large intestine. Are responsible for the disease “Trichinosis” HOOKWORMS which invade the small intestine of dogs, cats and humans. They cause anemia as they suck blood voraciously ASCARIDS which invade the human intestine and are responsible for the disease Ascariasis PINWORMS which invade the upper parts of the colon. Males are 1-4mm and females are 8-13 mm in length. FILARIDS which invade many different parts of the body are responsible for a range of diseases (incl. elephantiasis and Loa Loa)

5. Ascariasis Caused by Ascaris lumbricoides Ascaris infection is prevalent in tropical regions with poor hygiene Host becomes infected by ingestion of food contaminated with fecal matter containing eggs Diagnosis is usually made when the worms are passed through stool or vomit Upon autopsy, a 2 year old South African girl was found to have 796 worms in her ileum

6. Life cycle of Ascaris lumbricoides Upon ingestion of the eggs the larvae hatch, burrow through the intestine, reach the lungs and then migrate up the respiratory tract Upon ingestion of the eggs the larvae hatch, burrow through the intestine, reach the lungs and then migrate up the respiratory tract The larvae are then re- swallowed and mature in the intestine & grow up to 30 cm in length The larvae are then re- swallowed and mature in the intestine & grow up to 30 cm in length Larvae anchor themselves to the intestinal wall Larvae anchor themselves to the intestinal wall See next slide for detailed life cycle See next slide for detailed life cycle Ascaris larva developing inside egg Larvae exiting egg

7. 1. Adult worms live small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces 2-3. Fertilized eggs develop embryos and become infective after 18 days to several weeks after ingested depending on the environmental conditions 4-5. The larvae hatch & invade the intestinal walls and travel via the circulatory system to the lungs.

8. 6. The larvae mature further in the lungs (10 to 14 days and then migrate to the throat, and are swallowed 7. Upon reaching the small intestine, they develop into adult worms 8. Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years.

9. Elephantiasis Elephantiasis is a disease characterized by a thickening of the skin and underlying tissues which can be caused by invasion of the lymph nodes by nematodes Nematodes are transmitted by mosquitoes that mature and lodge themselves in the lymph nodes of the host Affects the legs and genitals More prevalent in tropical climates with over 120 million people affected worldwide

10. Ecological Roles of Free-living Nematodes Are decomposers: they recycle bacteria, fungi and decaying, rotting organic matter back into the soil. This means they are very important to the chain of energy production and matter recycling of the earth.

11. Negative Effects of Parasitic Nematodes Parasitic Nematodes: Invade many different types of crops and often cause crop death Attack the bark of forest trees (pine wood nematode) Invade the intestine of many mammals and cause sickness and often eventual death if untreated. Soybean Cyst nematode: infects soybean plant crops and causes cysts on the plants

12. “If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes and oceans represented by a thin film of nematodes. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites.” N.A.Cobb (United States Department of Agriculture, 1914)