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PHYLUM NEMATODA

“The Roundworms”

Nematoda (Roundworms) • widely distributed

• living in soil, animals,

• fresh and marine water

• Most are free-living

• many are parasitic.

Roundworm

• tapered at both ends

• no segments

• thick outer covering = Cuticle

• protects them in harsh environments

– Stomach acid

• Covering is shed 4 times as they grow.

Round bodyshape

Nematoda (Roundworms)

Tapered ends

• no circular muscles

• lengthwise (longitudinal) muscles

• one muscle contracts

• another muscle extends

• causes them to move in a thrashing motion from side to side

Nematoda (Roundworms)

• Have a pseudocoelom

• simplest animals with a one way digestive tract – mouth to anus

MouthIntestine Anus

Round bodyshape

Nematoda (Roundworms)

• Eyespots very reduced in parasitic roundworms.

Nematoda (Roundworms)

• Approximately half of species are parasites

• about 50 species infect humans.

Examples:

Ascaris, Pinworms, Trichenella, and Hookworms

• the most common roundworm infection in humans

Ascaris

• children infected more often than adults

– Why?

• Eggs in soil

– enter through the mouth of humans

Life Cycle--– hatch in intestines

– move into bloodstream

– eventually to lungs

– coughed up

– swallowed

– begin the cycle again.

• most common human roundworm parasites in U.S.

• highly contagious

• eggs can survive for up to two weeks on surfaces

Pinworms

• live eggs ingested

• mature in host’s intestinal tract

• female pinworms exit host’s anus – itching!

• lay eggs on nearby skin

• eggs fall onto bedding or other surfaces

• Reintroduced to intestine by mouth

• Trichinella causes a disease called “trichinosis”

• Found in raw or undercooked meat

• Can be sexually transmitted

Trichinella

Trichinella

• common in humans in warm climates

• Obtained when walking barefoot on contaminated soil

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

Hookworms

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

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

Roundworm Parasites

• They also can infect fungi and can form symbiotic associations with bacteria that help plants obtain nitrogen from air

• Nematodes also can be used to control pests

• Life on Earth is very dependent on nematodes

• Billions of nematodes in every one - symbiosis