Ascaris Shown above Similarities to Platyhelminthes: Bilateral symmetry

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Unit 5 Notes #5 Phylum Aschelminthes (Nematoda) ROUNDWORMS


A) Body Plan:

-Unsegmented worms that are cylindrically shaped.

- Most are free-living, but our focus will be on those that are parasitic.

Ascaris Shown above
Similarities to Platyhelminthes:

1. Bilateral symmetry

2. Three tissue layers (mesoderm specialized to give rise to muscle and various internal organs)

3. Tegument and cuticle (protection)
Differences :

- Complete digestive tract (mouth to anus).

-Between the mesoderm and the gut is a fluid filled space called a Pseudocoelom (“False Cavity”)

B) Continuity-Reproduction:

-Sexes are separate in most roundworms

- In the female, there is a pair of long, thin, coiled ovaries that produce thousands of eggs every day.

- In the male, there is one testicle; its job is to produce sperm.

- After the eggs are fertilized, shell glands secrete a shell around the egg so when they are released they will be protected.

 C) Various Systems:
1. Digestive:
-Aschelminthes have a complete digestive system so materials move in one direction only. – More efficient

-As food is pushed through the digestive tract, it is digested and nutrients are absorbed. Undigested remains continue on through the tract and are eventually eliminated out the anus.

 2. Circulation & Respiration

- No circulatory or respiratory systems.

- Breathe and excrete metabolic wastes through their moist skin.

- The fluid in the pseudocoelom distributes digested foods and dissolved oxygen.

D) Advances of Aschelminthes over Platyhelminthes:

1) They have a complete gut; more efficient digestion.

 2) They are Dioecious (either male or female) and they only use sexual reproduction.

 3) They have a fluid filled body cavity (pseudocoelom), which contains their internal organs. The fluid in this cavity helps distribute materials and also provides a hydraulic (water) skeleton to push muscles against.

E) Roundworm Human Disorders

1) Parasitic blisters: “Guinea worms form ulcerating blisters in human skin.

2) Elephantiasis: The “Filarial worm” blocks lymph vessels. This causes massive swelling and deformities. Eye worms are a close relative of Filarial worms. Most often transmitted by biting insects (mosquitoes).

Elephantiasis Eye worms
3) Parasitic Anemia: “Hookworm”: Larvae invade

Human hosts by using hooks to burrow through the skin of bare feet to find their way into blood vessels. From there, they circulate up to the lungs where they burrow into the air passages of the lungs. They then travel to the throat, where they are swallowed and come to anchor into the intestines.

- These parasites feast on blood, leaving the host (human) short of blood therefore short of oxygen due to a reduction in the number of red blood cells.

Hookworm Mouth

- Many such hookworms belong to the Genus “Ascaris

Bolus of Ascaris worms rectally passed

4)  Trichinosis: -From the “Trichinella worm

- Invade host when host eats uncooked meat (pork)

- Set up in the intestine.

- After mating the worms can produce up to 1500 microscope larvae which burrow into the host’s blood vessels.

- After traveling in the blood vessels they burrow into the host’s (pig, human, rats etc) tissues (muscles, organs). There they form painful cysts.

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