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.