1. Phylum Nematoda & Rotifera
Section 34.2

2. General Characteristics:
Bilateral symmetry
Fluid filled body cavity
pseudocoelomate
Holds internal organs
Storage for sperm & eggs
Supports body
Structure that muscles can contract against

3. Phylum Nematoda Roundworms 1mm to 4ft Digestive tract with 2 openings
Long, slender bodies that taper at both ends
1mm to 4ft
Digestive tract with 2 openings
Anterior – mouth
Posterior – anus
One directional movement

4. Continued… Most have separate sexes Cuticle – protective covering
Free-living on land, salt and freshwater
15,000 species known
150 species parasitic to plants and animals
Humans are host to 50 species!

5. Ascaris: Roundworm parasite that lives in intestine
Pigs, horses, & humans
Can totally block host’s intestine
Up to a foot in length
Female produces 200,000 eggs/day

6. Gross!
Video
Surgery

7. Life Cycle: Eggs leave with feces and enter soil
Enter humans with contaminated
food and water
Larvae enter intestines and
move to blood stream, then
lungs, coughed up and swallowed back
to intestines where they mate and reproduce

8. Hookworms: Another intestinal parasite
Mouth has cutting plates that clamp onto intestine wall
Feed on host’s blood which may lead to anemia
May cause slow mental and physical development in children
Affects 1 billion people in tropical and subtropical regions

9. Hookworm
Enter host by boring through the feet
Video

10. Life Cycle: Eggs leave with feces Larvae develop in soil
Enter host’s feet
Hitch a ride with blood to the lungs
Coughed up and swallowed to intestines where adult develop

11. Trichinella: Video Infect humans and pigs
Adults embed in walls of intestine
Larvae travel via blood to muscles
Form cysts
Humans get it from eating undercooked pork
Causes disease trichinosis
Muscle pain & stiffness
Can cause death
Video

12. Other Parasitic Roundworms
1. Pinworm – most common in U.S.
Live and mate in lower intestine
Female crawls out at night and lays eggs around anus
Person scratches during sleep and spreads eggs to everything touched
Eggs ingested and hatch

13. Pinworm

14. 2. Filarial worms – 250 million people infected in tropics
Found in lymphatic system (collects excess fluid from blood vessels)
Can cause elephantiasis
Swollen limbs, skin hardens & thickens
Can cause heartworm
in dogs and cats
Spread by mosquitoes

15. Elephantiasis