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PHYLUM NEMATODA “The Roundworms”

Section 26.4 Summary– pages 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 body shape 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)

Section 26.4 Summary– pages Have a pseudocoelom simplest animals with a one way digestive tract – mouth to anus Mouth Intestine Anus Round body shape Nematoda (Roundworms)

Section 26.4 Summary– pages 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

Section 26.4 Summary– pages 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

Section 26.4 Summary– pages Trichinella causes a disease called “trichinosis” Found in raw or undercooked meat Can be sexually transmitted Trichinella

Section 26.4 Summary– pages 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