Nematoda Notes

Phylum Nematoda

• These worms live in soil, animals, both freshwater and marine environments.

• Some are free-living, but many are parasites.

Nematoda

• Roundworms are tapered at both ends.

• They have a thick outer covering, which they shed 4 times as they grow.

Nematoda

• This covering protects them in harsh environments.

• They lack circular muscles but have lengthwise muscles.

Nematoda

• Roundworms have a pseudocoelom (which means “false coelom”) and have bilateral symmetry.

• Roundworms have 2 body openings: a mouth and an anus.

• The free-living species have well-developed sense organs, such as eyespots.

Diversity of Roundworms

• There are about 50 species of roundworm that affect humans.

A. Roundworm Parasites of Humans

• Infection by Ascaris is the most common roundworm infection in humans.

• It occurs mostly in tropical areas. • Children become infected more

often than adults.

A. Roundworm Parasites of Humans

• The Ascaris eggs are found in soil and enter a human’s body through the mouth.

• The eggs hatch in the intestines, move into the bloodstream, and eventually to the lungs, where they are coughed up, swallowed, and begin the cycle again.

Human Roundworms

• Pinworms are the most common roundworm found in the United States.

• The highest incidence of infection is in children.

• These worms are highly contagious because eggs can survive for up to 2 weeks on surfaces.

Human Roundworms

• Its life cycle begins when live eggs are ingested.

• They mature in the host’s intestinal tract.

• Female pinworms exit the host’s anus and lay eggs on nearby skin.

• These eggs fall onto bedding or other surfaces.

Human Roundworms• Trichinella causes a disease called

trichinosis. • This roundworm can be ingested in

raw or undercooked pork, pork products, or wild game.

Human Roundworms

• It can be controlled by properly cooking meat.

Human Roundworms

• Hookworm infections are common in humans in warm climates where they walk on contaminated soil in bare feet.

• These cause people to feel weak and tired due to blood loss.

B. Roundworm Parasites of Other Organisms

• About 1200 species of nematodes cause diseases in plants.

• Nematodes can infect and kill pine trees, cereal crops, and food plants such as potatoes.

B. Roundworm Parasites of Other Organisms

• They are particularly attracted to plant roots, and cause a slow decline of the plant.

• They can also infect fungi, and can form symbiotic associations with bacteria.