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Home , Cestoda, Flatworm, Planarian, Sucker (zoology), Tegument (helminth), Trematoda

Flatworms and Section 3 Section 3 Roundworms FocusFocus Overview Objectives Before beginning this section review with your students the When you think of a , you probably visualize a creature with a ● Compare the three classes objectives listed in the Student long, tubular body, such as an . You might be less famil- of flatworms. 8B 8C TAKS 2 Edition. This section explains the iar with flatworms and roundworms. The flatworms are the largest ● Summarize the cycle characteristics and life histories of group of acoelomate . Although the is of a fluke. 8C TAKS 2 relatively simple, it is a great deal more complex than that of a flatworms and roundworms. ● Describe the body plan of or cnidarian. Flatworms have a middle layer, the Students will explore the three dif- a roundworm. 8C TAKS 2 . And unlike and cnidarians, the flatworm has ferent classes of flatworms, as well tissues that are organized into organs. ● Summarize the life as the anatomy of both flatworms The flatworm’s body is bilaterally symmetrical and flat, like a piece cycle of the roundworm and roundworms. Ascaris. 8C of tape or ribbon. As a result, each in the ’s body lies very TAKS 2 close to the exterior environment. This permits dissolved substances, Key Terms such as and , to pass efficiently through the Bellringer flatworm’s solid body by . In addition, portions of the flat- proglottid The word worm can refer to a wide worm’s highly-branched gastrovascular cavity run close to practically fluke variety of organisms. Ask students all of its tissues. This gives each cell ready access to food molecules. to think about what a worm is, and Most flatworms have no respiratory or . ask them to list on paper the names Flatworms belong to Platyhelminthes, which contains or describe the types of worms they three major classes: , , and . They can remember. Ask students where range in size from free-living forms less than 1 mm (0.04 in.) in these worms live and what they eat. length to parasitic intestinal tapeworms several meters long. Have volunteers share their descrip- tions with the rest of the . Turbellaria LS Verbal Almost all members of class Turbellaria are free-living marine flatworms, such as the one shown in Figure 14. However, marine flatworms are rarely studied by MotivateMotivate students because they are difficult to raise in captivity. Instead, students usu- Discussion/ ally study a freshwater turbellarian such Question as , one of a group of flatworms Ask students what they might do if commonly called . Dugesia is they were in a rowboat that had a shown in Up Close: , on the small leak. (Students may answer following page. Figure 14 Marine flatworm. Most free-living flatworms are marine that swim with that they would use a small container graceful wavelike movements. to bail out the water as it seeps in.) Explain to students that all - Evolutionary Milestone isms have mechanisms that help 3 Bilateral Symmetry them maintain proper water bal- Flatworms were likely the first bilaterally symmetrical , with left ance. Tell them that water seeps and right halves that mirror each other. Like all bilaterally symmetrical into Dugesia, the flatworm they animals, flatworms have a distinct anterior (cephalic) end. will study on the next page, like it 629 seeps into a leaky boat. Ask them to suggest ways in which Dugesia might maintain water balance. Chapter Resource File Planner CD-ROM (The expels water • Reading Organizers so that the animal does not swell up.) • Lesson Plans GENERAL LS Logical Bio 3E • Directed Reading • Reading Strategies • Supplemental Reading Guide • Active Reading GENERAL Journey to the Ants: A Story of • Data Sheet for Quick Lab GENERAL Scientific Exploration

Transparencies TT Bellringer TT Planarian

Chapter 28 • Simple 629 Up Close Up Close Planarian TAKS 2; TAKS 3

Planarian TAKS 2 Bio 8C, 10A; TAKS 3 Bio 7B ● Scientific name: Dugesia sp. Discussion Guide the discussion ● Size: Average length of 3–15 mm (0.1–0.6 in.) by posing the following questions: ● Range: Worldwide •Instead of a circulatory system ● Habitat: Cool, clear, permanent lakes and streams that delivers to tissues, ● Diet: Protozoans and dead and dying animals what does a planarian have? Dugesia feeding (Branches of the digestive tract reach the tissues directly.) Characteristics •How do planarians reproduce Sensory information gathered by Feeding Dugesia, a free-living flatworm, must extend asexually? (They tear themselves the is sent to the muscles by two main cords its muscular out of its centrally located mouth in two, and each half regenerates that are connected by cross branches. Light-sensitive in order to feed. to form a complete worm.) structures called eyespots are connected to the brain. Reproduction Dugesia reproduces asexually in the The eyespots are close to each other, giving Dugesia •How do planarians reproduce summer by attaching its posterior end to a stationary across-eyed appearance. sexually? (They are hermaphro- object and stretching until it breaks in two, each of which dites that fertilize each other’s Brain will become a complete animal. Sexual reproduction . Protective capsules surround also occurs. Individuals are , and two groups of fertilized eggs, which individuals simultaneously hatch in 2–3 weeks.) Female transfer to each other. reproductive Eggs of both individuals are system Eyespot Male fertilized and are released in reproductive clusters enclosed in a protective system capsule. Several capsules are

TTeacheach Nerve cord laid at a time, and the eggs inside hatch in 2 to 3 weeks. GENERAL Pore Activity Pharynx Writing Life of a Planarian Mouth Have your students imagine a Reproductive day in the life of a planarian and pore write a story about the planarian’s adventures. Their story should include information about the planarian’s nervous system, water Tubule balance, reproduction, feeding, Excretory system Intestine , and excretion. Caution them to avoid anthropomorphic Water Balance Because Dugesia’s body cells contain more solutes Digestion The highly branched descriptions of the planarian, than fresh water does, water continually enters its body by osmosis. intestine enables nutrients to pass though a little creative license Excess water moves into a network of tiny tubules that run the length of close to all of the flatworm’s tissues. should be allowed. Have students Dugesia’s body. Side branches are lined with many flame cells, specialized Nutrients are absorbed through the volunteer to read their stories to cells with beating tufts of cilia that resemble a candle flame. The beating intestinal wall. Undigested food is the class. LS Verbal TAKS 2 Bio 10A cilia draw water through pores to the outside of the worm’s body. expelled through the mouth. 630 Trends in Neurology Impulsive Invertebrates Scientists have used better understand the neurological bases of pp. 630–631 many types of invertebrates, including planari- learning. Also, researchers in Germany have Student Edition ans and other flatworms, to try and under- recently made a computer chip that can send TAKS Obj 1 Bio/IPC 2B, 2C TAKS Obj 2 Bio 8C stand more about nerve cells and the nervous signals to a single nerve cell in a living . TAKS Obj 2 Bio 10A system. More than 50 ago, biologists The leech’s nerve cell can return the signal TAKS Obj 3 Bio 7B used giant axons from to learn how back to the computer chip. The researchers TEKS Bio 7B, 8C, 10A nerve impulses travel along nerve-cell are hoping that this technology will help them TEKS Bio/IPC 2B, 2C processes. More recent experiments with develop computers that can communicate with Teacher Edition Aplysia, a large sea slug, have helped scientists nerve cells in a human body. Bio 3F TAKS Obj 1 Bio/IPC 2B, 2C TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B, 12B TEKS Bio 3F, 7B, 8C, 10A, 12B TEKS Bio/IPC 2B, 2C

630 Chapter 28 • Simple Invertebrates Observing Planarian Behavior Most bilaterally symmetrical organisms have organs con- centrated in one end of the animal. You can observe how this Observing arrangement affects the way they explore their environment. Planarian 2B 2C Materials TAKS 1 Behavior TAKS 1 Bio/IPC 2B, 2C eyedropper, live culture of , small culture dish with pond water, hand lens or dissecting microscope, forceps, and small Skills Acquired piece of raw liver (3–7 cm) Observing, comparing, Procedure evaluating conclusions 1. Using the tip of the eyedrop- 4. Observe the planarian’s 3. Contrast the feeding behav- Teacher’s Notes per, place a planarian in the response. If the planarian ior of planarians with that of culture dish with pond water. approaches the liver, move hydras, described earlier in Before students begin, demon- the liver to a different position. this chapter. strate how to place planarian in 2. Using the hand lens or dis- secting microscope, observe 5. Continue observing the pla- 4. Critical Thinking a culture. Planarians are pho- the planarian as it adjusts to narian for 5 minutes, moving Evaluating an Argument tonegative and should be kept its environment. Determine the liver frequently. Evaluate this statement: in the dark as much as possible. which end of the planarian Bilateral symmetry gives pla- Analysis Use opaque pans, and keep the contains sensory apparatus naria an advantage when for exploring the environment. 1. Describe the planarian’s feeding because sensory water temperature close to means of locomotion. organs are concentrated in 18˚C. Prior to the lab, avoid 3. Using forceps, place the liver one end. Support your opin- in the pond water about 1 cm 2. Describe how the planarian feeding the planarians for a few ion with the observations you behind the planarian. responded to the liver. days. This will increase their made on planaria. feeding response during the lab. Answers to Analysis 1. Planarians move by contract- Cestoda ing and expanding their body Class Cestoda is made up of a group Figure 15 Tapeworm as they grip the surface. They of parasitic flatworms commonly A tapeworm’s body consists of a head and a series often turn their head from side called tapeworms. Tapeworms use of proglottids. to side as they move. their suckers and a few hooklike structures, shown in Figure 15, to per- Hooks Anterior end 2. Planarians likely will turn their manently attach themselves to the heads in the direction of the inner wall of their ’s intestines. liver before moving toward it. Food is then absorbed from the host’s 3. Hydras are relatively station- intestine directly through the tape- Ovary ary feeders and use cnidocytes worm’s skin. Tapeworms grow by pro- to sting and kill prey that is ducing a string of rectangular body moving towards them. sections called proglottids (proh Planarians are bilaterally GLAHT ihds) immediately behind symmetrical and have sensory their head. (Each proglottid is a com- plete reproductive unit, a fact that organs located at one end of makes it difficult to eliminate tape- their body. They are able to Proglottids worms once a person is infected.) Uterus detect food sources and move These sections are added continually Testes toward them. during the life of the tapeworm. The 4. Answers will vary. Students long, ribbonlike body of a tapeworm should support their argu- may grow up to 12 m (40 ft) long. ments with their observations. 631

Cultural Using the Figure GENERAL Awareness Have students study the different Tapeworm Students may pre- beef consumed in the United States is not parts of the tapeworm shown in sume that tapeworm infections are relatively federally inspected, and lightly infected beef Figure 15. Ask them to hypothesize rare among people living in developed coun- can be missed during inspections. As a result, the advantages of the hooks on the tries. Even in the United States, however, if a person eats undercooked roast beef, ham- anterior end and the redundancy of tapeworms from pigs and cattle can infect burgers, or steaks from an infected animal, the body sections. (hook to hold on humans. Researchers estimate that about the chance of becoming infected with beef to the host’s intestinal wall, redun- 1 percent of American cattle are infected with tapeworm is significant. TAKS 3 Bio 12B dancy to aid in proliferation of the beef tapeworms. A significant fraction of all tapeworm) LS Visual TAKS 3 Bio 12B

Chapter 28 • Simple Invertebrates 631 Most tapeworm infections occur in , and about a dozen different kinds of tapeworms commonly infect humans. One www.scilinks.org of the tapeworms that infects humans is the beef tapeworm, Topic: Flukes Keyword: HX4084 saginata. Beef tapeworm larvae live in the muscle tissue of infected TTeach,each, continuedcontinued cattle, where they form enclosed fluid-filled sacs called cysts. Humans become infected when they eat infected beef that has not Activity GENERAL been cooked to a temperature high enough to kill the larvae. Writing Flukes Have students research flukes using the Trematoda Internet. Have students write a The largest flatworm class, Trematoda, consists of parasitic worms report summarizing their findings. called flukes. Some flukes are endoparasites, or parasites that live Ask students to illustrate their inside their hosts. Endoparasites have a thick protective covering of reports and share them with the cells called a tegument that prevents them from being digested by class. LS Verbal TAKS 3 Bio 12B their host. Other flukes are ectoparasites, or parasites that live on the outside of their hosts. Flukes have very simple bodies with few organs. Flukes do not Using the Figure have well-developed digestive systems. Rather, they take their nour- Have students analyze Figure 16 ishment directly from their hosts. Flukes have one or more suckers from the perspective of a public that they use to attach themselves to their host. They use their mus- health investigator. Divide the class cular pharynx to suck in nourishment from the host’s body fluids. into small groups of two or three Most flukes have complex life cycles involving more than one host, students, and have them devise a one of which may be a human. Blood flukes of the plan to combat blood fluke are responsible for the infections. LS Logical Co-op Learning Figure 16 Schistosoma life cycle disease (shihs tuh soh MIE uh sihs), a major public TAKS 3 Bio 12B In the life cycle of blood flukes, are intermediate hosts and health problem in the tropics. humans are final hosts. occurs when people use or Teaching Tip GENERAL wade in water contaminated with Graphic Organizer Refer students Schistosoma larvae. The larval para- to their graphic organizer from sites bore through a person’s skin Eggs Section 1. Divide the class into and make their way to blood vessels small groups and ask them to fill in in the intestinal wall. They block Final blood vessels, resulting in bleeding the cells for flatworm and round- host Larvae enter blood vessels, of the intestinal wall and damage to worms. Ask the class to list at least mature, and the liver. As shown in Figure 16, the three major structures and their lay eggs. life cycle of blood flukes includes a LS Visual TAKS 2 Bio 10A functions. Eggs penetrate particular species of as an inter- intestine and exit with . mediate host.

Egg with developing Larval form that infects final host

Hatches in water

Larval form that infects Adult male blood flukes are thick-bodied, snail Intermediate host while adult females are threadlike. 632

Graphic Organizer Use this graphic organizer with Teaching Tip on this page. pp. 632–633 Student Edition Animal groups Lifestyles Structures/functions TAKS Obj 2 Bio 8C Flatworms Free-living or and sperm cells/ reproduction TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 12B parasitic Flame cells/excretion TEKS Bio 8C, 10A, 12B Pharynx/feeding Teacher Edition TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 12B TAKS Obj 4 IPC 9D TEKS Bio 3D, 8C, 10A, 12B TEKS IPC 9D

632 Chapter 28 • Simple Invertebrates