Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 27–2 Roundworms Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is a Roundworm? What Is a Roundworm? Most species of roundworms are free-living, inhabiting soil, salt flats, aquatic sediments, and water, from polar regions to the tropics. Others are parasitic and live in hosts. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is a Roundworm? Roundworms are unsegmented worms that have pseudocoeloms and digestive systems with two openings—a mouth and an anus. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is a Roundworm? This cavity is partially lined with tissue derived from the mesoderm and is called a pseudocoelom, meaning, “false coelom.” Roundworms such as hookworms are unsegmented worms that have a pseudocoelom and a digestive system with a mouth and an anus. Roundworms develop from three germ layers, and a pseudocoelom forms between the endoderm and mesoderm layers. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is a Roundworm? Roundworms have a digestive tract with two openings. Food moves in one direction through the digestive tract of roundworms. Any food that is not digested leaves the body through the anus. Copyright Pearson Prentice Hall

Form and Function in Roundworms Feeding Many free-living roundworms use grasping mouthparts and spines to catch and eat other small animals. Copyright Pearson Prentice Hall

Form and Function in Roundworms Respiration, Circulation, and Excretion Roundworms exchange gases and excrete metabolic waste through their body walls. They depend on diffusion to carry nutrients and waste through their bodies. Copyright Pearson Prentice Hall

Form and Function in Roundworms Movement Fluid in the pseudocoelom and muscles extending the length of their bodies function as a hydrostatic skeleton. Aquatic roundworms contract muscles to move like snakes through the water. Soil-dwelling roundworms push their way through the soil by thrashing around. Copyright Pearson Prentice Hall

Form and Function in Roundworms Reproduction  Roundworms reproduce sexually. Most species have separate sexes. Parasitic roundworms often have life cycles that involve two or three different hosts or several organs within a single host. Copyright Pearson Prentice Hall

Human Ascarid Reproduction Copyright Pearson Prentice Hall

Roundworms and Human Disease Parasitic roundworms include trichinosis-causing worms, filarial worms, ascarid worms, and hookworms. Copyright Pearson Prentice Hall

Roundworms and Human Disease Trichinosis-Causing Worms  Adult Trichinella worms live and mate in the intestines of their hosts. Larvae travel through the bloodstream and burrow into organs and tissues. 50 µm Encysted juveniles Muscle tissue Copyright Pearson Prentice Hall

Roundworms and Human Disease Trichinella completes its life cycle only when another animal eats muscle tissue containing these cysts. Humans can get trichinosis by eating raw or incompletely cooked pork. Copyright Pearson Prentice Hall

Roundworms and Human Disease Filarial Worms  Filarial worms are threadlike worms that live in the blood and lymph vessels of birds and mammals. They are transmitted by mosquitoes. Causes Elephantiasis Copyright Pearson Prentice Hall

Roundworms and Human Disease Ascarid Worms  Ascaris lumbricoides is a serious parasite of humans and many other vertebrate animals. It absorbs digested food from the host’s small intestine. Copyright Pearson Prentice Hall

Roundworms and Human Disease Ascaris Life Cycle 1 Human ingests food or water containing Ascaris eggs. Ascaris lumbricoides fill the host’s intestine. These worms absorb the host’s digested food and can cause severe malnutrition. Blockage of the intestine can be severe enough that it causes death. Copyright Pearson Prentice Hall

Roundworms and Human Disease Ascaris Life Cycle 2 The eggs travel to the small intestine and develop into larvae. Ascaris lumbricoides fill the host’s intestine. These worms absorb the host’s digested food and can cause severe malnutrition. Blockage of the intestine can be severe enough that it causes death. Copyright Pearson Prentice Hall

Roundworms and Human Disease Ascaris Life Cycle 3 Larvae enter blood vessels and are carried to the lungs Copyright Pearson Prentice Hall

Roundworms and Human Disease Ascaris Life Cycle 4 Larvae are coughed up and swallowed. They then travel to the small intestine where they develop to maturity Ascaris lumbricoides fill the host’s intestine. These worms absorb the host’s digested food and can cause severe malnutrition. Blockage of the intestine can be severe enough that it causes death. Copyright Pearson Prentice Hall

Roundworms and Human Disease Ascaris Life Cycle 5 Eggs are released and leave the host in faces. Ascaris lumbricoides fill the host’s intestine. These worms absorb the host’s digested food and can cause severe malnutrition. Blockage of the intestine can be severe enough that it causes death. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ascarids Ascarids taken from children of one village. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Heartworm Copyright Pearson Prentice Hall

Roundworms and Human Disease Hookworms  Hookworm eggs hatch and develop in the soil. They use sharp toothlike plates and hooks to burrow into the skin and enter the bloodstream. Copyright Pearson Prentice Hall

Roundworms and Human Disease Hookworms travel through the blood of their host to the lungs and down to the intestines. There, they suck the host’s blood, causing weakness and poor growth. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Rare Nematode Attacks! Gigantus wormius Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 27–2 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 27–2 In roundworms, the body cavity that forms between the endoderm and mesoderm is the ganglion. hydrostatic skeleton. pseudocoelom. coelom. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 27–2 All of the following are parasitic roundworms EXCEPT tapeworms filarial worms hookworms ascarid worms Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 27–2 Characteristics of roundworms include a digestive system with one opening and a pseudocoelom. one opening but no pseudocoelom. two openings and a pseudocoelom. two openings but no pseudocoelom. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 27–2 Gas exchange and excretion of metabolic wastes in roundworms occurs via a complex system of alveoli. through their body walls by diffusion. through excretory tubules. by flame cells. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 27–2 The roundworms called ascarids cause harm by causing serious body swelling. burrowing into body tissues and causing pain. causing malnutrition. causing internal bleeding. Copyright Pearson Prentice Hall

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