1. Section 2: Roundworms and Rotifers
Roundworms and rotifers have a more highly evolved gut than flatworms. K
What I Know W
What I Want to Find Out L
What I Learned

2. Essential Questions
What are the similarities between the features of roundworms and flatworms?
How can roundworms be identified based on movement?
What are the ways humans risk contracting roundworm parasites?
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Roundworms and Rotifers

3. Vocabulary Review New cilia hydrostatic skeleton trichinosis
Roundworms and Rotifers
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4. Body Structure of Roundworms
Roundworms are in phylum Nematoda, and often called nematodes.
Pseudocoelomates, bilaterally symmetric, cylindrical, unsegmented worms.
Found in marine, freshwater, and terrestrial environments.
Can be parasitic or free-living
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Roundworms and Rotifers

5. Body Structure of Roundworms
Feeding and digestion
Most roundworms are free-living, but some are parasites.
Free-living feed on a variety of food sources
Have a one-way digestive tract, a major evolutionary step associated with pseudocoelomates.
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Roundworms and Rotifers

6. Body Structure of Roundworms
Respiration, circulation, excretion, and response to stimuli
No circulatory or respiratory organs, depend on diffusion
Most roundworms exchange gases/excrete wastes through their outer body coverings.
Nematodes have ganglia and associated nerve cords.
Respond to touch, chemicals, and some respond to light
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Roundworms and Rotifers

7. Body Structure of Roundworms
Movement
Muscles run the length of the roundworm’s body
The muscles pull against the outside body wall and the pseudocoelom, which acts as a hydrostatic skeleton, fluid within a closed space that provides rigid support.
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Roundworms and Rotifers

8. Body Structure of Roundworms
Reproduction
Roundworms reproduce sexually, with internal fertilization.
In free-living worms, larvae hatch from eggs and develop into adults.
In parasitic worms, larval development is more complicated, and often involves various parts of the host body.
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Roundworms and Rotifers

9. Diversity of Roundworms
Trichinella worms
Cause a disease called trichinosis, contracted by eating raw or undercooked pork products
Burrow into the intestines of hosts, such as humans, pigs, and other mammals.
Hookworms
Commonly contracted in warm climates by humans who walk barefoot over contaminated soils.
Travels through the circulatory system to the lungs, then to the esophagus where it is swallowed and transported to the intestines.
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Roundworms and Rotifers

10. Diversity of Roundworms
Ascarid worms
Most common worm infection in humans
Contracted through unwashed vegetables or contaminated soils
Pinworms
Most common nematode parasite in humans in the United States
Spread most frequently among children
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Roundworms and Rotifers

11. Diversity of Roundworms
Filarial worms
Tropical parasites spread through mosquito intermediary
Causes elephantiasis, swelling of the lymph system, in humans
Source of heartworm in cats and dogs
Nematodes in plants
Some species of roundworm cause disease in plants
Most species of nematodes are harmless or beneficial to plants
Can be used as biological control for pests.
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Roundworms and Rotifers

12. Rotifers Rotifer features and movement
Bilaterally symmetric pseudocoelomates with rings of cilia around their mouths
Move through the water by means of their cilia
Posterior end has “toes” that secrete an adhesive material that allows them to attach themselves to surfaces
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Roundworms and Rotifers

13. Rotifers Organ systems of rotifers
Gather food with cilia and transfer it to a complete digestive tract
Exchange gases and excrete metabolic wastes through diffusion
Have sensory bristles and an eyespot
Reproduce both sexually and asexually depending on environmental conditions
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Roundworms and Rotifers

14. Review Essential Questions Vocabulary
What are the similarities between the features of roundworms and flatworms?
How can roundworms be identified based on movement?
What are the ways humans risk contracting roundworm parasites?
Vocabulary
hydrostatic skeleton
trichinosis
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Roundworms and Rotifers