Roundworms Bonneville High School Invertebrate Zoology

26.4 Section Objectives – page 711 Compare and contrast the structural adaptations of roundworms and flatworms. Section Objectives: Identify the characteristics of four roundworm parasites.

Section 26.4 Summary– pages Roundworms belong to the phylum Nematoda. What is a roundworm? They are widely distributed, living in soil, animals, and both freshwater and marine environments. Most roundworm species are free- living, but many are parasitic. Roundworm

Roundworms are tapered at both ends. What is a roundworm? They have a thick outer covering, which they shed four times as they grow, that protects them in harsh environments. Mouth Intestine Anus Round body shape

They lack circular muscles but have lengthwise muscles. What is a roundworm? As one muscle contracts, another muscle relaxes. This alternating contraction and relaxation of muscles causes roundworms to move in a thrashing fashion.

Roundworms have a pseudocoelom and are the simplest animals with a tubelike digestive system. What is a roundworm? Roundworms have two body openings— a mouth and an anus. Mouth Intestine Anus Round body shape

Section 26.4 Summary– pages What is a roundworm? The free-living species have well-developed sense organs, such as eyespots, although these are reduced in parasitic forms. Mouth Intestine Anus Round body shape

Section 26.4 Summary– pages Approximately half of the described roundworm species are parasites, and about 50 species infect humans. Diversity of Roundworms

Roundworm parasites of humans -Ascaris lumbrioides (The large roundworm of Humans): Female Ascaris may lay 200,000 eggs a day which are passed out in the host’s feces. Embryos develop infective juveniles within 2 weeks. Infection occurs when eggs are ingested with uncooked vegetables or when children put soiled fingers or toys in their mouths. The host swallows the eggs. The eggs hatch into tiny juveniles which burrow through the intestinal wall into veins. Once in the blood they travel to the lungs then to the trachea. They then can be coughed up and swallowed then travel to the stomach and mature about 2 months after the eggs were ingested. The parasite is rarely fatal unless there is heavy infestation. Infection rates tend to be highest in children, and males tend to be more heavily infected than females.

Hookworms -Hookworms: Named so because the anterior ends curve dorsally, suggesting a hook. These worms can reach up to 11 mm long. They have large plates in their mouths which cut into the intestinal all where they suck blood and pump it though their intestines. It is partially digested and absorbs the nutrients. They can be a source of anemia in patients. This disease can result in retarded mental and physical growth and a general loss in energy for children. Eggs pass through the feces and juveniles hatch in the soil. They live on the bacteria. When human skin comes in contact with infected soil, infective juveniles burrow through the skin to the blood and reach the lungs and finally the intestine similar to Ascaris.

Section 26.4 Summary– pages Hookworm infections are common in humans in warm climates where they walk on contaminated soil in bare feet. Roundworm parasites of humans Hookworms cause people to feel weak and tired due to blood loss.

Pinworms are the most common human roundworm parasites in the United States. Roundworm parasites of humans Pinworms are highly contagious because eggs can survive for up to two weeks on surfaces.

Pinworms: -Pinworms (Enterobius vermicularis): Common parasites in the United States. The parasites live in the large intestine and cecum. Females, up to about 12 mm in length, migrate to the anal region at night and lay their eggs. Scratching the resultant itch contaminates hands and bedclothes. Eggs develop rapidly and become infective within 6 hours at body temperature. When they are swallowed they hatch in the duodenum, and the worms mature in the large intestine.

Its life cycle begins when live eggs are ingested. They mature in the host’s intestinal tract. Roundworm parasites of humans Female pinworms exit the host’s anus— usually as the host cell sleeps—and lay eggs on nearby skin. These eggs fall onto bedding or other surfaces.

Filarial Worms -Filarial worms: The worms live in the lymphatic system, and females are as long as 10 cm. Females release live young, tiny microfilariae into the blood and lymphatic system. As they feed, mosquitos ingest microfilariae, which develop inside the mosquitos to the infective stage. They escape from the mosquito when it is feeding again on a human and penetrate the wound made by the mosquito bite. Filarial worms include elephantiasis, onchocerciasis, and dog heartworm. See Fig (Pg 312)

Roundworm parasites of humans -Trichina Worm: Can cause trichinosis. Adult worms burrow in the mucosa of the small intestine where females produce living young. Juveniles penetrate blood vessels and are carried though-out the body, where they may be found in almost any tissue or body space. Eventually they penetrate skeletal muscle cells. Juveniles cause astonishing redirection of gene expression in their host cell, which loses its striations and becomes a nurse cell that nourishes the worm. When raw or poorly cooked meat containing encysted juveniles is swallowed, the worms are liberated into the intestine where they mature. These worms can infect a wide variety of mammals in addition to humans, including pigs, rats, cats, and dogs.

Section 26.4 Summary– pages Nematodes can infect and kill pine trees, cereal crops, and food plants such as potatoes. Roundworm parasites of other organisms They are particularly attracted to plant roots and cause a slow decline of the plant.

Section 26.4 Summary– pages They also can infect fungi and can form symbiotic associations with bacteria. Roundworm parasites of other organisms Nematodes also can be used to control pests.