Roundworms and rotifers have a more highly evolved gut than flatworms.

Section 2: Roundworms and Rotifers

KWhat I Know

WWhat I Want to Find Out

LWhat I Learned

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?

Roundworms and RotifersCopyright © McGraw-Hill Education

Review• cilia

New• hydrostatic skeleton• trichinosis

Roundworms and RotifersCopyright © McGraw-Hill Education

Vocabulary

Roundworms and RotifersCopyright © McGraw-Hill Education

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

Roundworms and RotifersCopyright © McGraw-Hill Education

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.

Roundworms and RotifersCopyright © McGraw-Hill Education

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

Roundworms and RotifersCopyright © McGraw-Hill Education

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.

Roundworms and RotifersCopyright © McGraw-Hill Education

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.

Roundworms and RotifersCopyright © McGraw-Hill Education

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.

Roundworms and RotifersCopyright © McGraw-Hill Education

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

Roundworms and RotifersCopyright © McGraw-Hill Education

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.

Roundworms and RotifersCopyright © McGraw-Hill Education

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

Roundworms and RotifersCopyright © McGraw-Hill Education

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

Roundworms and RotifersCopyright © McGraw-Hill Education

Review

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?

Vocabulary• hydrostatic skeleton• trichinosis