Chapter 29: Echinoderms and Invertebrate Chordates

Refer to pages 4T-5T of the Teacher Guide for an explanation of the National Science Education Standards correlations. Teacher Classroom Resources

Assessment Resources Additional Resources

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Echinoderms and Invertebrate Chordates

Echinoderms and Invertebrate Chordates

TransparenciesReproducible MastersSection

Echinoderms

InvertebrateChordates

Section 29.1

Section 29.2

Teacher Classroom Resources

Reinforcement and Study Guide, pp. 127-129Critical Thinking/Problem Solving, p. 29BioLab and MiniLab Worksheets, p. 129Laboratory Manual, pp. 205-210Content Mastery, pp. 141-142, 144

Reinforcement and Study Guide, p. 130Concept Mapping, p. 29Critical Thinking/Problem Solving, p. 29BioLab and MiniLab Worksheets, pp. 130-132Content Mastery, pp. 141, 143-144 L1

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Section Focus Transparency 71Basic Concepts Transparency 50Basic Concepts Transparency 51

Section Focus Transparency 72Reteaching Skills Transparency 43

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LSAssessment Resources Additional Resources

Spanish ResourcesEnglish/Spanish AudiocassettesCooperative Learning in the Science ClassroomLesson Plans/Block Scheduling

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Chapter Assessment, pp. 169-174MindJogger VideoquizzesPerformance Assessment in the Biology ClassroomAlternate Assessment in the Science ClassroomComputer Test BankBDOL Interactive CD-ROM, Chapter 29 quiz

Chapter 29 OrganizerChapter 29 Organizer

Activities/FeaturesObjectivesSection

EchinodermsNational Science EducationStandards UCP.1-5; A.1, A.2;C.3, C.5, C.6 (1 session, 1/2block)

InvertebrateChordatesNational Science EducationStandards UCP.1, UCP.2,UCP. 4, UCP.5; A.1, A.2;C.3, C.5, C.6; G.1-3 (2 ses-sions, 1/2 block)

1. Compare similarities and differencesamong the classes of echinoderms.

2. Interpret the evidence biologists havefor determining that echinoderms areclose relatives of chordates.

3. Summarize the characteristics of chordates.

4. Explain how invertebrate chordates are related to vertebrates.

5. Distinguish between sea squirts and lancelets.

MiniLab 29-1: Examining Pedicellariae, p. 788Inside Story: A Sea Star, p. 790Problem-Solving Lab 29-1, p. 792Investigate BioLab: Observing Sea UrchinGametes and Egg Development, p. 800Physics Connection: Hydraulics of Sea Stars,p. 802

MiniLab 29-2: Examining a Lancelet, p. 797Inside Story: A Tunicate, p. 798Problem-Solving Lab 29-2, p. 799

Section 29.2

Section 29.1

MATERIALS LIST

BioLabp. 800 microscope, microscope slides (5),coverslips (5), petri dish, dropper (2),test tube, beaker (2), sea water, live seaurchins (male and female), syringe withneedle, potassium chloride solution

MiniLabsp. 788 microscope, prepared slide ofsea star pedicellariae, paper, pencilp. 797 stereomicroscope, microscopeslide, forceps, metric ruler, preservedspecimen of Branchiostoma cali-forniense (Amphioxus)

Alternative Labp. 796 microscope, prepared slides ofsea urchin development and lancelets

Quick Demosp. 789 stereomicroscope, live seaurchin, toothpickp. 789 dropperp. 791 heavy bookp. 795 preserved specimens of tuni-cates and lanceletsp. 796 microscope, prepared slide oflancelet cross section

Need Materials? Contact Carolina Biological Supply Company at 1-800-334-5551or at http://www.carolina.com

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Products Available FromGlencoeTo order the following products,call Glencoe at 1-800-334-7344:CD-ROMNGS PictureShow: Structure ofInvertebratesTransparency SetNGS PicturePack: Structure ofInvertebrates

Index to NationalGeographic MagazineThe following articles may beused for research relating to thischapter:“Pillar of Life,” by George Grall,July 1992.

Teacher’s Corner

Key to Teaching StrategiesKey to Teaching Strategies

Level 1 activities should be appropriatefor students with learning difficulties.Level 2 activities should be within theability range of all students.Level 3 activities are designed for above-average students.ELL activities should be within the abilityrange of English Language Learners.

Cooperative Learning activitiesare designed for small group work.These strategies represent student prod-ucts that can be placed into a best-workportfolio.These strategies are useful in a blockscheduling format.

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The following multimedia resources are available from Glencoe.

Biology: The Dynamics of LifeCD-ROM

Exploration: The Five KingdomsExploration: EchinodermsExploration: SymmetryBioQuest: Biodiversity Park

Videodisc ProgramStarfishes

The Secret of Life SeriesSea StarsChordate Body PlanAction of Tube Feet

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http://www.carolina.com

Section

What Is an Echinoderm?Members of the phylum Echino-

dermata have a number of unusualcharacteristics that easily distinguishthem from members of any otheranimal phylum. Echinoderms moveby means of hundreds of hydraulic,suction cup-tipped appendages andhave skin covered with tiny, jawlikepincers. Echinoderms (ih KI nuhdurmz) are found in all the oceans ofthe world.

Echinoderms have endoskeletonsIf you were to examine the skin of

several different echinoderms, youwould find that they all have a hard,spiny, or bumpy endoskeleton cov-ered by a thin epidermis. The long,pointed spines on a sea urchin areobvious. Sea stars, sometimes called

starfishes, may not appear spiny atfirst glance, but a close look revealsthat their long, tapering arms, calledrays, are covered with short, roundedspines. The spiny skin of a seacucumber consists of soft tissueembedded with small, platelike struc-tures that barely resemble spines.The endoskeleton of all echinodermsis made primarily of calcium carbon-ate, the compound that makes uplimestone.

Some of the spines found on seastars and sea urchins have becomemodified into pincerlike appendagescalled pedicellariae (PED ih sihl AHR

ee ay). An echinoderm uses its jawlikepedicellariae for protection and forcleaning the surface of its body. Youcan examine these structures in theMiniLab on the following page.

29.1 ECHINODERMS 787

Think about what the best defensemight be for a small animal thatmoves slowly in tide pools on the

seashore. Did you think of armor, spines, orperhaps poison as methods of protection?Sea urchins are masters of defense—someuse all three methods. The sea urchin looksdifferent from the feather star and fromthe sea star on the facing page, yetall three belong to the same phy-lum. What characteristics dothey have in common? Whatfeatures determine whether ananimal is an echinoderm?

SECTION PREVIEW

ObjectivesCompare similaritiesand differences amongthe classes of echino-derms.Interpret the evidencebiologists have fordetermining that echinoderms are closerelatives of chordates.

Vocabularyraypedicellariatube feetampullawater vascular systemmadreporite

29.1 Echinoderms

Feather star(above) and seaurchin (inset)

OriginWORDWORD

echinodermFrom the Greekwords echinos,meaning “spiny,”and derma, meaning“skin.” Echinodermsare spiny-skinnedanimals.

pedicellariaeFrom the Latinword pediculus,meaning “littlefoot.” Pedicellariaeresemble little feet.

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Section 29.1

BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Use with Chapter 29,Section 29.1

The word echinoderm comes from the Greek echinos,meaning “spiny,” and derm, meaning “skin.” Why do youthink this name was given to this group of organisms?

How is the radial symmetry of these saltwater animalsan advantage?

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Brittle star

Sea urchin

Sand dollar

PrepareKey ConceptsThe characteristics common toechinoderms are presented. Thediversity of echinoderms is con-sidered. Deuterostome develop-ment is examined in terms of itsevolutionary significance.

Planning■ Obtain droppers for the Quick

Demos.■ Make photocopies of the

inner, shaded area of Figure29.6 for the Reteach.

1 FocusBellringer Before presenting the lesson,display Section Focus Trans-parency 71 on the overhead pro-jector and have students answerthe accompanying questions.

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Assessment PlannerAssessment PlannerPortfolio Assessment

MiniLab, TWE, pp. 788, 797Assessment, TWE, p. 789Problem-Solving Lab, TWE, p. 792Portfolio, TWE, p. 792

Performance AssessmentBioLab, SE, pp. 800-801MiniLab, SE, pp. 788, 797Alternative Lab, TWE, pp. 796-797

Assessment, TWE, pp. 793, 799Problem-Solving Lab, TWE, p. 798

Knowledge AssessmentSection Assessment, SE, pp. 793, 799Chapter Assessment, SE, pp. 803-805Assessment, TWE, p. 796BioLab, TWE, pp. 800-801

Skill AssessmentAlternative Lab, TWE, pp. 796-797

Echinoderms andInvertebrate Chordates

What You’ll Learn■ You will compare and

contrast the adaptations of echinoderms.

■ You will distinguish the fea-tures of chordates by examin-ing invertebrate chordates.

Why It’s ImportantBy studying how echinodermsand invertebrate chordatesfunction, you will enhance yourunderstanding of evolutionaryrelationships between thesetwo groups.

Observing a Sand DollarExamine the brittle skeleton ofa sand dollar. Notice the petal-like marking on its upper sur-face. What kind of symmetrydoes this organism exhibit?

To find outmore about

echinoderms and invertebratechordates, visit the GlencoeScience Web Site.www.glencoe.com/sec/science

29

GETTING STARTEDGETTING STARTED

ChapterChapter

A sea star extends its stom-ach from its mouth andengulfs a sea urchin. Hourslater, the sea star draws its stomach back in andmoves away. All that’s leftof the urchin is the bumpyglobe you see here. Even itsspines are gone.

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Theme DevelopmentEvolution is a major theme inthis chapter. Students study howechinoderm larvae and inverte-brate chordates show similaritiesto certain vertebrates. The themeof systems and interactions isobvious as students learn how theechinoderms and invertebratechordates are adapted to andinteract with their environments.

Chapter 29Chapter 29

MultipleLearningStyles

Look for the following logos for strategies that emphasize different learning modalities.

Kinesthetic Meeting IndividualNeeds, p. 788; Quick Demo,

pp. 789, 791; Activity, p. 795Visual-Spatial Quick Demo,pp. 789, 796; Tech Prep, p. 789;

Project, p. 790; Portfolio, p. 795;Reteach, p. 799

Linguistic Biology Journal,p. 790Naturalist Portfolio, p. 792;Check for Understanding,

p. 793; Reteach, p. 793; Quick Demo, p. 795

GETTING STARTED DEMOGETTING STARTED DEMO

Visual-Spatial Use liveor preserved sea stars or

sea urchins to point out thephysical characteristics ofechinoderms. Elicit from stu-dents how the meaning of theterm echinoderm relates tothe features of animals in thisgroup. Echinoderm means“spiny skin.” The animals clas-sified in this phylum havespinelike structures coveringtheir bodies.

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If time does not permit teach-ing the entire chapter, use theBioDigest at the end of theunit as an overview.

Resource ManagerResource Manager

Section Focus Transparency 71and Master

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http://www.glencoe.com/sec/science

Connection at the end of this chapter.The water vascular system is a

hydraulic system that operates underwater pressure. Water enters andleaves the water vascular system of asea star through the madreporite(MAH dray pohr ite), a sievelike, disk-shaped opening on the upper surfaceof the echinoderm’s body. You canthink of this disk as being like the lit-tle strainer that fits into the drain in asink and keeps large particles out ofthe pipes. You can find out how a seastar eliminates wastes by reading theInside Story on the next page.

Finally, tube feet function in gasexchange and excretion. Gases areexchanged and wastes are eliminatedby diffusion through the thin walls ofthe tube feet.

Echinoderms have varied nutritionAll echinoderms have a mouth,

stomach, and intestines, but theirmethods of obtaining food vary. Seastars are carnivorous and prey onworms or on mollusks such as clams.Most sea urchins are herbivores andgraze on algae. Brittle stars, sea lilies,and sea cucumbers feed on dead anddecaying matter that drifts down tothe ocean floor. Sea lilies capture thissuspended organic matter with theirtentaclelike tube feet and move it totheir mouths.

Echinoderms have a simple nervous system

Echinoderms have no head orbrain, but they do have a centralnerve ring that surrounds the mouth.Nerves extend from the nerve ringdown each ray. Each radial nervethen branches into a nerve net thatprovides sensory information to theanimal. Echinoderms have cells thatdetect light and touch, but most donot have sensory organs. Sea stars arean exception. A sea star’s body con-

sists of long, tapering rays thatextend from the animal’s central disk.At the tip of each ray, on the under-side, is an eyespot, a sensory organconsisting of a cluster of light-detect-ing cells. When walking, sea starscurve up the tips of their rays so thatthe eyespots are turned up and out-ward. This enables a sea star to de-tect the intensity of light coming fromevery direction.

Echinoderms have bilaterally symmetrical larvae

If you examine the larval stages ofechinoderms, you will find that theyhave bilateral symmetry, a featuremore common to chordates. The cil-iated larva that develops from thefertilized egg of an echinoderm isshown in Figure 29.3. Throughmetamorphosis, the free-swimming larvae make dramatic changes in bothbody parts and in symmetry.The bilateral symmetry ofechinoderm larvae indicatesthat echinoderm ancestorsalso may have had bilateralsymmetry, suggesting aclose relationship to thechordates. You can observesea urchin development inthe BioLab at the end of this chapter.


Figure 29.2Tube feet enable seastars and other echin-oderms to creepalong the ocean bot-tom or to pry openthe shells of bivalves.

Figure 29.3These sea urchin lar-vae are only 1 mm insize. The larval stageof echinoderms isbilateral, eventhough the adultstage has radial symmetry.

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Portfolio Ask students tomake a table showing the differ-ent groups of echinoderms, thetype of food they eat, andwhether or not they move aroundto find their food. Ask them torelate the type of food to the ani-mals’ methods of locomotion.Have them include their table andexplanation in their portfolios.

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AssessmentAssessment

Examining Pedicellariae Echinodermsmove by tube feet. They also have tinypincers on their skin called pedicellariae.

Procedure! Observe a slide of sea star pedicellar-

iae under low-power magnification.CAUTION: Use caution when work-ing with a microscope and slides.

@ Record the general appearance of one pedicellaria. Whatdoes it look like?

# Make a diagram of one pedicellaria under low-powermagnification.

$ Record the size of one pedicellaria in micrometers.

Analysis1. Describe the general appearance of one pedicellaria.2. What is the function of this structure?3. Explain how the structure of pedicellariae assists in their

function.

MiniLab 29-1MiniLab 29-1

Echinoderms have radial symmetryYou may remember that radial sym-

metry is an advantage to animals thatare stationary or move slowly. Radialsymmetry enables these animals tosense potential food, predators, and

other aspects of their environmentfrom all directions. Observe the radialsymmetry, as well as the various sizesand shapes of spines, of each echino-derm pictured in Figure 29.1.

The water vascular systemAnother characteristic unique to

echinoderms is the water vascular sys-tem that enables them to move,exchange gases, capture food, andexcrete wastes. Look at the close-upof the underside of a sea star inFigure 29.2. You can see that groovesfilled with tube feet run from the areaof the sea star’s mouth to the tip ofeach ray. Tube feet are hollow, thin-walled tubes that end in a suction cup.Tube feet look somewhat like minia-ture droppers. The round, muscularstructure called the ampulla (AM puhlah) works something like the bulb ofa dropper. The end of a tube footworks like a tiny suction cup. Eachtube foot works independently of theothers, and the animal moves alongslowly by alternately pushing out andpulling in its tube feet. You can learnmore about the operation of thewater vascular system in the Physics

Figure 29.1All echinoderms have radial symmetryas adults and an endoskeleton com-posed primarily of calcium carbonate.

Pedicellariae

Observing and Inferring Magnification: 223

A living sand dollarhas a solid, immov-able skeleton com-posed of flattenedplates that are fusedtogether.

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A sea lily’s featheryrays are composed of calcified skeletalplates covered with an epidermis.

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A brittle star’s long, snakelikerays are composed of overlap-ping, calcified plates coveredwith a thin layer of skin cells.

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2 Teach

Purpose Students will observe the pin-cherlike structure of pedicellar-iae.

Process Skillsobserve and infer, compare andcontrast, draw a conclusion, mea-sure in SI

Teaching Strategies■ Review the procedure for mea-suring objects under the micro-scope.■ Prepared slides are availablefrom biological supply houses.

Expected ResultsStudents will observe that pedi-cellariae have a pincherlikeappearance and measure close to250µm in length.

Analysis1. Student answers will vary—

pincherlike, plierslike, for-cepslike

2. allows animal to graspobjects, clean itself of debris,protection

3. These pincherlike organsallow the sea star to pinchpotential predators whenthey touch the animal. Theirshape also allows the sea starto clean itself by picking offmaterials that become stuckto its body.

Portfolio Have studentswrite a lab report that summarizestheir results and place it in theirportfolios. Use the PerformanceTask Assessment List for LabReport in PASC, p. 47.

Visual LearningHave students examine the ani-mals shown in Figure 29.1closely. Challenge them to iden-tify the lines of symmetry foreach organism that has radialsymmetry. L1

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MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

Visually ImpairedKinesthetic Provide visuallyimpaired students with dried speci-

mens of various echinoderms. Allow stu-dents to handle the specimens so they canfeel the shapes, sizes, and characteristicspiny skins of these animals.P

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Quick DemoQuick Demo

Visual-Spatial Have stu-dents observe the pedicel-

lariae of a live sea urchin undera stereomicroscope and makesketches of their observations.Have them touch one pedicel-laria with a toothpick toobserve the structure’sresponse.

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Kinesthetic Provideeach student with a

dropper. Have them squeezethe air from the dropper, andthen, while still applying pres-sure to the rubber end of thedropper, touch the droppertip to their finger. They shouldrelease the pressure on thedropper and observe how thedropper holds to their finger.Explain that this is similar tothe suction action of the tubefeet of a sea star.P

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CD-ROMBiology: The Dynamics of LifeExploration: The Five Kingdoms

Disc 3

Raising Sea StarsVisual-Spatial Ask students to visit asaltwater aquarium at a local zoo or

pet shop. Have them visit when the sea starsand sea urchins are being fed. Ask studentsto observe and record sea star feedingbehavior when live clams or oysters are

added to the tank. Ask them to interview the person in charge of taking care of theaquarium to find out what daily tasks thecaretaker must perform to maintain the seastars and sea urchins. Have students reporttheir findings to the class.

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BioLab and MiniLab Work-sheets, p. 129 L2

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Diversity ofEchinoderms

Approximately 6000 species ofechinoderms exist today. More thanone-third of these species are in theclass Asteroidea (AS tuh royd ee uh), towhich the sea stars belong. The fourother classes of living echinodermsare Ophiuroidea (OH fee uh royd eeuh), the brittle stars; Echinoidea (ehkihn OYD ee uh), the sea urchins andsand dollars; Holothuroidea (HOH

loh thuh royd ee uh), the sea cucum-bers; and Crinoidea (cry NOYD eeuh), the sea lilies and feather stars.

Sea starsMost species of sea stars have five

rays, but some have more. Somespecies may have more than 40 rays.The rays are tapered and extend fromthe central disk. You have alreadyread about the characteristics of seastars that make them a typical exam-ple of echinoderms.

Brittle starsAs their name implies, brittle stars

are extremely fragile, Figure 29.4. Ifyou try to pick up a brittle star, partsof its rays will break off in your hand.This is an adaptation that helps thebrittle star survive an attack by apredator. While the predator is busywith the broken-off ray, the brittlestar can escape. A new ray will regen-erate within weeks.

Brittle stars do not use their tubefeet for locomotion. Instead, theypropel themselves with the snakelike,slithering motion of their flexiblerays. They use their tube feet to passparticles of food along the rays andinto the mouth in the central disk.

Sea urchins and sand dollarsSea urchins and sand dollars are

globe- or disk-shaped animals covered

with spines, as Figure 29.4 shows.They do not have rays. The circular,flat skeletons of sand dollars have afive-petaled flower pattern on thesurface. A living sand dollar is cov-ered with minute, hairlike spines thatare lost when the animal dies. A sanddollar has tube feet that protrudefrom the petal-like markings on itsupper surface. These tube feet aremodified into gills. Tube feet on theanimal’s bottom surface aid in bring-ing food particles to the mouth.

Sea urchins look like living pin-cushions, bristling with long, usually

Figure 29.4Echinoderms areadapted to life in avariety of habitats.

Basket stars, akind of brittle star,live on the softsubstrate foundbelow deep oceanwaters.

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Sea urchins oftenburrow intorocks to protectthemselvesfrom preda-tors andrough water.

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Sand dollars bur-row into the sandyocean bottom.They feed on tinyorganic particlesfound in the sand.

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Ray

Nerve ring

Mouth

Reproductiveorgan

Endoskeletalplates

Radialnerve Ampula

Radialcanal

Ringcanal

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A Sea Star

If you ever tried to pull a sea star from a rock where it isattached, you would be impressed by how unyielding and

rigid the animal seems to be. Yet at other times, the animalshows great flexibility, such as when it rights itself after beingturned upside down.

Critical Thinking How is radial symmetry useful to a sea star? Blood sea star

INSIDESSTORTORYY

INSIDE

Endoskeleton A sea star can maintain arigid structure or be flexible because it hasan endoskeleton in the form of calciumcarbonate plates just under its epidermis.The plates are connected by bands of soft tissue and muscle. When the muscles are contracted, the body becomes firm and rigid. When the muscles are relaxed, the body becomes flexible.

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Madreporite Water flowsin and out of the watervascular system throughthe madreporite.

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Tube feet The suctionaction of tube feet,caused by the contractionand relaxation of theampulla, is so strong that the sea star’s muscles can open a clam or oyster shell.

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Eyespots When moving, a sea star curvesup the tips of its rays so that the eyespotsare turned up and outward. Echinodermeyespots distinguish between light anddark but do not form images.

44Digestive gland Thedigestive gland gives offchemicals for digestion.

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Anus Wasteproducts of diges-tion are eliminatedthrough the anus.

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Pedicellariae The pincerlikepedicellariae on the rays of the

sea star will pinch any animalthat tries to crawl over it.

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Stomach To eat, a seastar pushes its stomachout of its mouth andspreads the stomach over the food. Powerfulenzymes secreted by thedigestive gland turn solidfood into a soupy liquidthat the stomach caneasily absorb. Then thesea star pulls the stom-ach back into its body.

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Pedicellaria

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IINSIDENSIDESSTORTORYY

INSIDE

Purpose Students will learn about thestructural and behavioral adapta-tions of a sea star.

Teaching Strategies■ Ask students to observe a livesea star in action. They can use ahand lens to observe the tube feetas the sea star “walks” or “climbs”a surface of a marine aquarium.

Visual Learning■ Make photocopies of the

Inside Story diagram withoutthe labels of the structures.Number the parts and explainto students how each partfunctions and how the partsenable the sea star to survive inits environment. Have stu-dents use this information tolabel the diagram.

Critical ThinkingRadial symmetry enables animalsthat move slowly to sense andobtain potential food, escapepredators, and sense otheraspects of their environmentfrom all directions.

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P R O J E C TEchinoderm Display

Visual-Spatial Ask a group of stu-dents to create a bulletin board dis-

play of echinoderms. Have them highlightthe features of echinoderms. Ask them to find examples of everyday objects thatshow similar traits. Students may use sand-paper to model the texture of echinodermskin.

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Kinesthetic When a seastar tries to open a clam

or oyster, its muscles mustovercome the force exerted bymollusk muscles that are try-ing to keep the shells closed. A sea star opens a bivalve byapplying a steady, unrelentingpressure until the bivalve’smuscles tire. Tell students tohold their arms straight out tothe side with their palms up.Their arm muscles representthe bivalve’s muscles. Have apartner place a heavy book onthe students’ open palms. Askthem to time how long theycan hold their arms out beforedropping the book. The bookrepresents the sea star’s mus-cles.

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Cultural DiversityJapan and the Sea Urchin Industryin MaineIntroduce students to what is rapidly becom-ing a $100 million international industry—the importation of Maine sea urchins toJapan. Once a remote destination in winter,coastal Maine has become a magnet forJapanese businesspeople because of the seaurchin, a creature once considered to be a

pest to commercial fisheries.Sea urchins are prized in Japan as uni, a

sushi delicacy. The Japanese value the seaurchin for the quality of its eggs, called roe.Today more than 95% of all sea urchins har-vested in Maine are sent to Japan. The har-vesting of sea urchins is also becoming bigbusiness in California.

BIOLOGY JOURNAL BIOLOGY JOURNAL

Sea Star LifeLinguistic Have students write anessay in which they describe one day

in the life of a sea star. Allow a few stu-dents to read their essays. Have other stu-dents discuss which parts of the essayswere scientific and which were creativefiction.

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CD-ROMBiology: The Dynamicsof Life

Exploration: EchinodermsDisc 4Exploration: SymmetryDisc 4

VIDEODISCThe Secret of LifeSea Stars

Biology: The Dynamics of LifeStarfishes (Ch. 39)Disc 1, Side 2, 49 sec.

!7;F8C"

!:áÄ"


Laboratory Manual, pp. 205-210

Critical Thinking/ProblemSolving, p. 29

Basic Concepts Transparency50 and Master

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Origins of EchinodermsThe earliest echinoderms may

have been bilaterally symmetrical asadults, and probably were attached tothe ocean floor by stalks. Anotherview of the earliest echinoderms isthat they were bilateral and free-swimming. The development ofbilateral larvae is one piece of evi-dence biologists have for placingechinoderms as the closest inverte-brate relatives of the chordates.


Section AssessmentSection Assessment

Understanding Main Ideas1. How does a sea star move? Explain in terms of

the water vascular system of echinoderms.2. Describe the differences in symmetry between

larval echinoderms and adult echinoderms.3. How are sea cucumbers different from other

echinoderms?4. Compare how sea urchins and sea cucumbers

obtain food.

Thinking Critically5. How do the various defense mechanisms among

the echinoderm classes help deter predators?

6. Classifying Prepare a key that distinguishesamong classes of echinoderms. Include informa-tion on features you may find significant. Formore help, refer to Organizing Information inthe Skill Handbook.

SKILL REVIEWSKILL REVIEW

PRESENTCENOZOICPALEOZOICPRECAMBRIAN MESOZOIC

Crinoids600 species

Asteroids1500 species

Echinoids950 species

Ophiuroids2000 species

Holothuroids1500 species

Figure 29.6Most echinoderms have been foundas fossils from the early Paleozoicera. Fossils of brittle stars are found beginning at a later period.

Recall that most invertebrates showprotostome development, whereasdeuterostome development appearsmainly in chordates. The echino-derms represent the only major groupof deuterostome invertebrates.

Because the endoskeletons ofechinoderms easily fossilize, there isa good record of this phylum.Echinoderms, as a group, date fromthe Paleozoic era, as shown in Figure29.6. More than 13 000 fossil specieshave been identified.

ANIMALS

3 AssessCheck for Understanding

Naturalist Ask students touse Figure 29.6 to explain

the phylogenetic history ofechinoderms.

ReteachNaturalist Give studentsphotocopies of the inner,

shaded part of the phylogeneticdiagram in Figure 29.6. Havethem place each class in its cor-rect position. Ask them to listalso the identifying features ofeach class.

ExtensionHave students research and re-port on the relationship betweenthe crown-of-thorns sea star andcoral reefs.

Performance Have stu-dents prepare a demonstration forthird graders that explains thewater vascular system of a sea star.Ask them to present this demon-stration to the class using a work-ing model.

4 CloseActivityShow a film about echinodermsand their interactions with othermarine organisms.

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What makes sea cucumbersrelease gametes? The orangesea cucumber lives in groups of100 or more per square meter.In the spring, these sea cucum-bers produce large numbers ofgametes (eggs and sperm), whichthey shed in the water all at thesame time. The adaptive value ofsuch behavior is that fertilization of many eggs is assured.When one male releases sperm, the other sea cucumbers inthe population, both male and female, also release theirgametes. Biologists do not know whether the sea cucumbersrelease their gametes in response to a seasonal cue, such asincreasing day length or increasing water temperature, orwhether they do this in response to the release of sperm byone sea cucumber.

AnalysisDesign an experiment that will help to determine

whether sea cucumbers release eggs and sperm in responseto the release of sperm from one individual or in response toa seasonal cue.

Thinking CriticallyIf you find that female sea cucumbers release 200 eggs in

the presence of male sperm and ten eggs in the presence ofwater that is warmer than the surrounding water, whatwould you do in your next experiment?

Problem-Solving Lab 29-1Problem-Solving Lab 29-1 Designing anExperiment

pointed spines. They have long, slen-der tube feet that, along with thespines, aid the animal in locomotion.

The sea urchin’s spines protect itfrom predators. In some species, sacslocated near the tips of the spinescontain a poisonous fluid that isinjected into an attacker, further pro-tecting the urchin. The spines alsoaid in locomotion and in burrowing.Burrowing species move their spinesin a circular motion that grinds awaythe rock beneath them. This action,which is aided by a chewing action ofthe mouth, forms a depression in therock that helps protect the urchinfrom predators and from wave actionthat could wash it out to sea.

Sea cucumbersSea cucumbers are so called because

of their vegetablelike appearance,shown in Figure 29.5. Their leatherycovering allows them to be moreflexible than other echinoderms; theypull themselves along the ocean floorusing tentacles and tube feet. Whensea cucumbers are threatened, theyexhibit a curious behavior. They mayexpel a tangled, sticky mass of tubesthrough the anus, or they may rup-ture, releasing some internal organsthat are regenerated in a few weeks.These actions confuse their predators,giving the sea cucumber an opportu-nity to move away. Sea cucumbersreproduce by shedding eggs andsperm into the water, where fertiliza-tion occurs. You can find out moreabout sea cucumber reproduction inthe Problem-Solving Lab on this page.

Sea lilies and feather starsSea lilies and feather stars resem-

ble plants in some ways. Sea lilies arethe only sessile echinoderms. Featherstars are sessile only in larval form.The adult feather star uses its feath-ery arms to swim from place to place.

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Figure 29.5Sea lilies and featherstars use their featheryrays to capture down-ward-drifting organicparticles (a). Seacucumbers trap organicparticles by sweepingtheir mucous-coveredtentacles over theocean bottom (b).

a

b

Orange sea cucumber

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Purpose Students will design an experi-ment to determine the stimulusfor release of sea cucumbergametes.

Process Skillsdesign an experiment, identifyand control variables

Teaching Strategies■ Ask students to think of strate-gies that animals may use toensure aquatic fertilization. Likelyanswers will include releasing largenumbers of eggs and sperm, andreleasing eggs and sperm at the sametime.

Thinking CriticallyTo design an experiment, stu-dents may decide to keep a groupof female sea cucumbers inaquariums, control all environ-mental variables, and then releasesperm into the water to see if thiscauses the release of eggs.

Portfolio Explain to stu-dents that sea stars have beenfound to spawn on the same dayas sea cucumbers. Ask if this indi-cates that the stimulus for spawn-ing is environmental or is inresponse to one male first releas-ing sperm. Ask students to writetheir responses in their portfolios.Use the Performance Task As-sessment List for Making Obser-vations and Inferences in PASC,p. 17. PP

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Problem-Solving Lab 29-1Problem-Solving Lab 29-1

PortfolioPortfolio

Echinoderm PhylogenyNaturalist Provide students withechinoderm fossils. Include as many

different kinds as possible and use pho-tographs of fossils you don’t have. Askstudents to arrange the fossils and pho-tographs to illustrate the phylogeny ofthis group.

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CD-ROMBiology: The Dynamics of LifeBioQuest: Biodiversity Park

Disc 3, 4

Section AssessmentSection AssessmentSection Assessment1. A sea star moves by regulation of its

water vascular system. Tube feet attachto a surface, the sea star moves itselfforward, and the suction is released.

2. Larval echinoderms are bilaterally sym-metrical, whereas adult echinodermsare radially symmetrical.

3. Sea cucumbers are tubular and have aleathery outer covering instead of hard

plates.4. Sea urchins graze on algae; sea cucum-

bers feed on dead matter that drops tothe ocean floor.

5. The rigid endoskeleton helps protectechinoderms from their enemies.Spines and poison glands also protectechinoderms. Adult echinoderms moveby walking, whereas larval forms are

free swimming. If an echinoderm suchas a sea star loses part of a ray, it canbe regenerated. Sea cucumbers canexpel their digestive tracts and grownew ones.

6. Students’ keys will vary considerably,but all should utilize the branchingnature of keys described in the SkillHandbook. 793


Content Mastery, p. 142Reinforcement and Study

Guide, pp. 127-129Basic Concepts Transparency

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Section

794 ECHINODERMS AND INVERTEBRATE CHORDATES

What Is an InvertebrateChordate?

The chordates most familiar to youare the vertebrate chordates—chor-dates that have backbones, such asbirds, fishes, and mammals, includinghumans. But the phylum Chordata(kor DAHT uh) includes three sub-phyla: Urochordata, the tunicates

(sea squirts); Cephalochordata, thelancelets; and Vertebrata, the verte-brates. In this section you will exam-ine the tunicates and lancelets—invertebrate chordates that have nobackbones. You will study the verte-brate chordates in the next unit.

Invertebrate chordates may not lookmuch like fishes, reptiles, or humans,but like all other chordates, they havea notochord, a dorsal hollow nervecord, gill slits, and muscle blocks atsome time during their development.In addition, all chordates have bilateralsymmetry, a well-developed coelom,and segmentation. The features sharedby invertebrate and vertebrate chor-dates are illustrated in Figure 29.7.You can observe these features ininvertebrate chordates in the Problem-Solving Lab later in this section.

The brightly colored object pictured hereis a sea squirt. As one of your closestinvertebrate relatives, it is placed,

along with humans, in the phylum Chordata.At first glance, this sea squirt may seem toresemble a sponge more than its fellow chor-dates. It is sessile, and it filters foodparticles from water it takes inthrough the opening at the topof its body. What characteris-tics could a human—or a fishor a lizard, for that mat-ter—share with this colorful,ocean-dwelling organism?

SECTION PREVIEW

ObjectivesSummarize the charac-teristics of chordates.Explain how inverte-brate chordates arerelated to vertebrates.Distinguish betweensea squirts and lancelets.

Vocabularynotochorddorsal hollow

nerve cordgill slit

29.2 InvertebrateChordates

Figure 29.7Chordate characteris-tics—the notochord,dorsal hollow nervecord, gill slits, andmuscle blocks—areshared by inverte-brate as well as ver-tebrate chordates.

Mouth

Dorsal hollownerve cord Notochord

Gill slitsMuscle blocks

Anus Tail

Sea squirt and ahuman (inset)

All chordates have a notochordAll chordate embryos have a noto-

chord (NOHT uh kord)—a long,semirigid, rodlike structure locatedbetween the digestive system and thedorsal hollow nerve cord. The noto-chord is made up of large, fluid-filledcells held within stiff, fibrous tissues.In invertebrate chordates, the noto-chord is retained into adulthood. Butin vertebrate chordates, this structureis replaced by a backbone. Inverte-brate chordates do not develop abackbone.

The notochord develops just afterthe formation of a gastrula frommesoderm on what will be the dorsalside of the embryo. The physical sup-port provided by a notochord enablesinvertebrate chordates to make pow-erful side-to-side movements of

the body. These movements propelthe animal through the water at agreat speed.

All chordates have a dorsal hollow nerve cord

The dorsal hollow nerve cord inchordates develops from a plate ofectoderm that rolls into a hollowtube. This occurs at the same time asthe development of the notochord.The sequence of development of thedorsal hollow nerve cord is illustratedin Figure 29.8. This tube is composedof cells surrounding a fluid-filledcanal that lies above the notochord.In most adult chordates, the cells inthe posterior portion of the dorsalhollow nerve cord develop into thespinal cord. The cells in the anteriorportion develop into a brain. A pair

29.2 INVERTEBRATE CHORDATES 795

Figure 29.8After gastrulation, organs beginto form in a chordate embryo.

The notochord forms frommesoderm on the dorsal sideof a developing embryo.

AA

The dorsal hollow nerve cordoriginates as a plate of dorsalectoderm just above thedeveloping notochord.

BB The edges of this plate ofectoderm fold inward, eventu-ally meeting to form a hollowtube surrounded by cells. Thedorsal hollow nerve cordpinches off from the ectodermand develops into the centralnervous system of the animal.

CC

Cells migrate from the meeting margins of the neural tube andeventually form other organs,including bones and muscles.

DD

Notochord

Neuralfold

Neuralplate

Ectoderm

Outer layerof ectoderm

Dorsal hollownerve cord

MesodermEndoderm

Neuralfold

Neuralplate



Cells that formbones andmuscle

Notochord

OriginWORDWORD

chordataFrom the Latinword chorda, mean-ing “cord.” Thephylum Chordataconsists of animalswith notochords.

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Section 29.2

PrepareKey ConceptsStudents will learn about inverte-brate chordates. They will distin-guish between sea squirts andlancelets and study the relation-ships of these animals to the ver-tebrates.

Planning■ Prepare syringes with potas-

sium chloride and gatherbeakers, glass slides, coverslips,and test tubes for the BioLab.

1 FocusBellringer Before presenting the lesson,display Section Focus Trans-parency 72 on the overhead pro-jector and have students answerthe accompanying questions.

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BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

AnusMuscle blocks

Tail

NotochordDorsal nerve cord

Gill Slits

Mouth

Use with Chapter 29,Section 29.2

Which of the structures shown on this animal are notfound on other animals you have studied so far?

What do you think the function of the notochord is?

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SECTION FOCUS

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Transparency Invertebrate ChordateStructures72


Naturalist Ask studentsto observe preserved or

mounted specimens of tuni-cates and lancelets. Ask themif they can see any characteris-tics that link these animals tovertebrate chordates. Elicitwhether the animals mighthave unseen characteristicsthat link them to vertebratechordates.

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ActivityKinesthetic Have studentsrun their fingers along their

backs to feel their backbones.Explain that the backbone isunique to vertebrates and formsfrom the notochord—the struc-ture that identifies all members ofthe phylum Chordata. Althoughall chordates have a notochord atsome time during their develop-ment, not all chordates havebackbones.

Visual LearningHave students explain how theInside Story on development inChapter 25 relates to Figure29.8.

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Tunicate ResearchAsk students to use the Internet and theirlocal library to do research on tunicates.Ask them to find out where tunicates liveand if any tunicate species are threatenedor endangered. Have students place theirfindings in their journals. L2

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PortfolioPortfolio

Water Movement in TunicatesVisual-Spatial Have students usethe diagram in the Inside Story on

page 798 to make a flowchart that tracesthe path of water through a sea squirt.Have students place their completed flow-charts in their portfolios.

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Internet Address Book

Note Internet addressesthat you find useful in

the space below for quick reference.

VIDEODISCThe Secret of LifeChordate Body Plan

!7;FLE"


Section Focus Transparency 72 andMaster

Concept Mapping, p. 29Reteaching Skills Transparency 43

and Master

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of nerves connects the nerve cord toeach block of muscles.

All chordates have gill slitsThe gill slits of a chordate are

paired openings located in the phar-ynx, behind the mouth. Many chor-dates have several pairs of gill slitsonly during embryonic development.Invertebrate chordates that have gillslits as adults use these structures tostrain food from the water. In somevertebrates, especially the fishes, thegill slits develop into internal gillsthat are adapted to exchange gasesduring respiration.

All chordates have muscle blocksMuscle blocks are modified body

segments that consist of stacked mus-cle layers. You have probably seenmuscle blocks when you ate a cookedfish. The blocks of muscle cause the

meat to separate easily into flakes.Muscle blocks are anchored by thenotochord, which gives the muscles afirm structure to pull against. As aresult, chordates tend to be moremuscular than members of otherphyla.

Muscle blocks also aid in move-ment of the tail. At some point indevelopment, all chordates have amuscular tail. As you know, humansare chordates, and during the earlydevelopment of the human embryo,there is a muscular tail that disap-pears as development continues. Inmost animals that have tails, thedigestive system extends to the tip ofthe tail, where the anus is located.Chordates, however, usually have atail that extends beyond the anus.You can observe many of the chor-date traits in a lancelet in theMiniLab on the next page.

Diversity ofInvertebrate Chordates

The invertebrate chordates belongto two subphyla of the phylum chordata: subphylum Urochordata,the tunicates (TEW nuh kaytz), alsocalled sea squirts, and subphylumCephalochordata, the lancelets.

Tunicates are sea squirtsMembers of the subphylum Uro-

chordata are commonly called tuni-cates, or sea squirts. Although adulttunicates do not appear to have anyshared chordate features, the larvalstage, as shown in Figure 29.9, has atail that makes it look similar to atadpole. Tunicate larvae do not feed,and are free swimming only for a fewdays after hatching. Then they settleand attach themselves with a suckerto boats, rocks, and the ocean bot-tom. Many adult tunicates secrete a

Figure 29.9Tunicate larvae areabout 1 cm long andare able to swim freelythrough the water (a).As adults, tunicatesbecome sessile filterfeeders enclosed in atough, baglike layer oftissue called a tunic (b).

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a

b

Examining a Lancelet Branchiostomacaliforniense is a small, sea-dwellinglancelet. At first glance, it appears to bea fish. However, its structural parts andappearance are quite different.

Procedure! Place the lancelet onto a glass slide.

CAUTION: Wear disposable latex gloves and handle pre-served material with forceps.

@ Use a dissecting microscope to examine the animal. CAUTION: Use care when working with a micro-scope and slides.

# Prepare a data table that will allow you to record the fol-lowing: General body shape, Length in mm, Head regionpresent, Fins and tail present, Nature of body covering,Sense organs such as eyes present, Habitat, Segmented body.

$ Indicate on your data table if the following can easily beobserved: gill slits, notochord, dorsal hollow nerve cord.

Analysis 1. How does Branchiostoma differ structurally from a fish?

How are its general appearance and habitat similar tothose of a fish?

2. Explain why you were not able to see gills, notochord, anda dorsal hollow nerve cord.

3. Using its scientific name as a guide, where might the habi-tat of this species be located?

MiniLab 29-2MiniLab 29-2tunic, a tough sac made of cellulose,around their bodies. Colonies oftunicates sometimes secrete just onebig tunic that has a common openingto the outside. You can find out howtunicates eat in the Inside Story on thenext page.

Only the gill slits in adult tunicatesindicate their chordate relationship.Adult tunicates are small, tubular ani-mals that range in size from micro-scopic to several centimeters long,about as big as a large potato. If youremove a tunicate from its sea home,it might squirt out a jet of water forprotection—hence the name seasquirt.

Lancelets are similar to fishesLancelets belong to the subphylum

Cephalochordata. They are small,streamlined, and common marineanimals, usually about 5 cm long, asFigure 29.10 shows. They spendmost of their time buried in the sandwith only their heads sticking out.Like tunicates, lancelets are filterfeeders. Unlike tunicates, however,lancelets retain all their chordate fea-tures throughout life.

Mouth


NotochordGill slitsin pharynx

Muscle blocksIntestine

Anus

Oral hood with tentaclesFigure 29.10Lancelets usually spend most of theirtime buried in the sand with only theirheads sticking out so they can filter tinymorsels of food from the water (a). Thelancelet’s body looks very much like atypical chordate embryo (b).

Observing

ba

Purpose Students will observe the externalappearance of lancelets.

Process Skillscompare and contrast, interpretdata, make and use tables, mea-sure in SI, observe and infer

Teaching Strategies■ Specimens are available frombiological supply houses.■ A hand lens may be substitutedfor a binocular microscope.

Expected ResultsLancelets have a long, tubularbody shape; length close to 50mm, head region, tail-like poste-rior; smooth body; no senseorgans. Students will not be ableto see a notochord, gill slits, or adorsal hollow nerve cord.

Analysis1. It has no sense organs, gills,

or fins. But it does have a dis-tinct head area. Fishes areclassified in the same phylumas lancelets—Chordata—butin subphylum Vertebrata,whereas lancelets are in sub-phylum Cephalochordata.

2. These structures are all inter-nal organs.

3. in the ocean along the coastof California

Portfolio Have studentswrite a paragraph explaining whylancelets are important in evolu-tion. Use the Performance TaskAssessment List for Writing inScience in PASC, p. 87. PP

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notochord, gill slits, muscle blocks, tail.6. Note the fishlike form of the lancelet.

Expected ResultsStudents should see all of the featureslisted above.Analysis

1. How does the size of the sea urchinblastula compare with that of thezygote? The blastula and the zygoteare the same size. The cells becomesmaller as development proceeds.

2. What does the symmetry of the larvaof a sea urchin imply about the evolu-tionary relationship between echino-derms and chordates? Echinoderms areclosely related to chordates.

3. What features of the lancelet place itin the phylum Chordata? dorsal hollownerve cord, notochord, gill slits, muscleblocks, tail

Skill Set up microscopes withslides showing features of lancelets andvarious stages of sea urchin develop-ment. Ask students to identify the partor sequence of development and statethe importance of the part for chordates.Use the Performance Task AssessmentList for Making Observations andInferences in PASC, p. 17. L2

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Alternative LabComparison of Sea Urchins and Lancelets

Purpose Students will compare sea urchin larvaewith adult lancelets.

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Materialscompound microscope, prepared slides ofsea urchin development, prepared slides oflanceletsProcedureGive students the following directions.

1. Observe slides of the unfertilized seaurchin egg, zygote, 2-cell stage, 4-cellstage, 8-cell stage, blastula, gastrula,and sea urchin larvae. Use low-powermagnification at first, then switch to

high-power magnification.2. Draw a diagram of each stage in the

order listed. Label each diagram withthe name of the stage.

3. Note how the size of the blastula com-pares with the size of the zygote. Notealso the size of the cells at each stage.

4. Examine a prepared slide of a lancelet.5. Find the following parts of the lance-

let and label them on a diagram youmake: dorsal hollow nerve cord, 796


Visual-Spatial Have stu-dents examine a prepared

slide of a cross section of alancelet. Explain that in lance-lets the notochord is presentthroughout the life of the ani-mal, while in vertebrates thenotochord is replaced by abackbone. They should also findthe dorsal hollow nerve cordabove the notochord and com-pare it with the notochord. Em-phasize that the function of thenotochord is to provide supportfor the animal.

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Knowledge Ask studentsto separate the following animalsinto groups based on the type ofnervous system each has. Theirlists should identify animals thathave a ventral nerve cord, thosethat have a dorsal hollow nervecord, and those that have someother nervous system arrange-ment: earthworm, snail, pla-narian, sea star, tunicate, clam,grasshopper, lancelet, spider,human. L3

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BioLab and MiniLab Work-sheets, p. 130 L2

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What does a slice through an invertebrate chordateshow? Why are tunicates and lancelets important? Beinginvertebrate chordates, they show three major structures thatare present at some time during all chordate development.

Analysis The diagram at

right shows a cross section of an inver-tebrate chordate. Your task is to determine what the various structures marked A-F are.

Thinking Critically1. What three structures are present in all chordates at

some time during their development? Does the cross-section diagram of the lancelet confirm your answer?Explain.

2. How would you know that the cross section was not from an echinoderm?

3. How might the cross section differ if it were taken from an adult tunicate? A young developing tunicate?

Problem-Solving Lab 29-2Problem-Solving Lab 29-2 Interpreting ScientificIllustrations

Although lancelets look somewhatsimilar to fishes, they have only onelayer of skin, with no pigment and noscales. Lancelets do not have a dis-tinct head, but they do have lightsensitive cells on the anterior end.They also have a hood that coversthe mouth and the sensory tentaclessurrounding it. The tentacles directthe water current and food particlestoward the animal’s mouth.

Origins of InvertebrateChordates

Because sea squirts and lanceletshave no bones, shells, or other hardparts, their fossil record is incom-plete. Biologists are not sure wheresea squirts and lancelets fit in thephylogeny of chordates. According toone hypothesis, echinoderms, inver-tebrate chordates, and vertebrates allarose from ancestral sessile animalsthat fed by capturing food in tenta-cles. Modern vertebrates probablyarose from the free-swimming larvalstages of ancestral invertebrate chor-dates. Recent discoveries of fossilforms of organisms that are similar toliving lancelets in rocks 550 millionyears old show that invertebratechordates probably existed beforevertebrate chordates.


Section AssessmentSection Assessment

Understanding Main Ideas1. Describe the four features of chordates.2. How are invertebrate chordates different from

vertebrates?3. Compare the physical features of sea squirts and

lancelets.4. How do sea squirts and lancelets protect them-

selves?

Thinking Critically5. What features of chordates suggest that you are

more closely related to invertebrate chordatesthan to echinoderms?

6. Designing an Experiment Assume that youhave found some tadpolelike animals in the waternear the seashore and that you can raise them in a laboratory. Design an experiment in which youwill determine whether the animals are larvae oradults. For more help, refer to Practicing ScientificMethods in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

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3 AssessCheck for UnderstandingAsk students to list invertebratechordate characteristics.

ReteachVisual-Spatial Give studentgroups a large piece of

paper. Have them diagram a lan-celet and label its typical inverte-brate chordate parts and theirfunctions.

ExtensionAsk students to research thephyla Hemichordata and Chae-tognatha. Ask them to reportabout the structural and behav-ioral adaptations of these animalsand their evolutionary relation-ships with echinoderms andchordates.

Performance Have stu-dents plan an exhibit for tunicatesat a public aquarium. Ask them toinclude in their plan suggestionsabout capture, transport, habitat,feeding, and general maintenance.

4 CloseActivityDevelop a table that compareslancelets and tunicates, discussingwhich features are common tovertebrates and invertebrates.

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Section AssessmentSection AssessmentSection Assessment1. notochord, dorsal hollow nerve cord, gill

slits, muscle blocks2. In invertebrate chordates, the notochord

is not replaced by a backbone.3. Sea squirts are small, tubular, stationary

filter feeders. Lancelets are shaped likefishes and can swim freely, but theyspend most of their time buried in thesand.

4. Sea squirts are covered with a thick tunic,and lancelets bury themselves in sand.

5. notochord, gill slits, muscle blocks, anddorsal hollow nerve cord

6. Watch the animals for several weeks tosee if they change their body shape andsymmetry. Watch for reproductive behav-ior or release of gametes.

Water

Mouth

Gill slits

Stomach

Anus

Intestine

Reproductiveorgans

Esophagus


A Tunicate

Tunicates, or sea squirts, are a group of about 1250 speciesthat live in the ocean. They may live near the shore or at

great depths. They may live individually, or several animals mayshare a tunic to form a colony.

Critical Thinking In what ways are sponges and tunicates alike?

Purple bell tunicate

INSIDESSTORTORYY

INSIDE

Excurrent siphon Water leavesthe body of the animal throughthe excurrent siphon. When atunicate is disturbed, it mayforcefully spout water from itsmouth and excurrent siphonsimultaneously.

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Ciliated grooveDuring filter feeding,food is trapped bymucus secreted in aciliated groove. Thefood and mucus aredigested in the ani-mal’s intestine.

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Heart The heart of the tunicate is unusualbecause it pumps bloodin one direction for several minutes andthen reverses direction.

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Tunic Tunicates are covered with a layer of tissue called atunic. Some tunics are thick and tough, and others are thinand translucent. All protect the animal from predators.

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Pharynx The pharynxis lined with gill slitsand cilia. The beatingof the cilia causes a cur-rent of water to movethrough the animal.Food is filtered out,and dissolved oxygen isremoved from thewater in the pharynx.

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Incurrent siphon Water comes into the animal through the incurrentsiphon, the animal’s mouth.

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IINSIDENSIDESSTORTORYY

INSIDE

Purpose Students will learn about thestructural and behavioral charac-teristics of tunicates.

Teaching Strategies■ Ask students to compare thefilter feeding of tunicates withthe filter feeding of sponges andbivalves.

Visual Learning■ Review with students the char-

acteristics of tunicates thatmake them invertebrate chor-dates.

■ Show students live specimensof tunicates and have themcompare the specimens withthe diagram.

Critical ThinkingSponges and tunciates are bothfilter feeders.

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Purpose Students will interpret a cross-section slice of a lancelet.

Process Skillsinterpret scientific illustrations,observe and infer, think critically

Teaching Strategies■ Review the procedure formaking a cross-section slice.■ Review the orientation of thecross-section slice in relation tothe whole animal. Use a cucum-ber to illustrate the view and ori-entation by making a cross-sectionslice through the fruit.

Thinking Critically

1. Gill slits, muscle blocks,notochord, dorsal hollownerve cord; student answersshould agree that these arepresent.

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Problem-Solving Lab 29-2Problem-Solving Lab 29-2

2. Echinoderms would have tube feet and awater vascular system, but no noto-chord, dorsal hollow nerve cord, gillslits, or muscle blocks.

3. An adult tunicate would have gill slitsbut no notochord or dorsal hollow nervecord. A young developing tunicate hasall of these structures.

Performance Ask students to drawan events chain that sequences the steps theywould need to take to determine that a speci-men is a lancelet rather than an immaturefish. Use the Performance Task AssessmentList for Events Chain in PASC, p. 91. L2

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Going FurtherGoing Further

1. Compare and Contrast Compareeggs and sperm, noting numbersreleased, numbers observedunder low power, size, and abilityto move.

2. Predicting Based on the patternof fertilization, predict the reasonfor the large number of gametesreleased in nature.

3. Observing Describe the behaviorof sperm when they first come incontact with an egg.

4. Observing How does an unfertil-ized egg differ in appearance

from a fertilized egg? Draw botheggs in your data table.

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

Project Continue to observe fertilized eggsand note the stages of development. Keep arecord of time after fertilization and corre-sponding changes in development.

To find out more aboutechinoderm develop-

ment, visit the Glencoe Science Web Site.www.glencoe.com/sec/science

female sea urchin. Share gametecells.

9. Use a clean dropper to transfer adrop of sperm from the beaker to amicroscope slide. Observe underlow power without a cover slip.

10. Add a cover slip and observeunder high power. Note themovement of sperm. Draw severalsperm cells and indicate their sizein µm. Note the approximatenumber of sperm cells present.

11. Repeat steps 9 and 10 for eggcells. In step 10, use only lowpower to observe egg cells.

12. For this step, work with a partner.While one partner transfers some

sperm to the slide with egg cellsusing a clean dropper, the otherpartner should observe under lowpower.

13. Observe the process of fertiliza-tion and note any changes thatoccur to the egg. Record yourobservations in a data table.

14. When fertilization has beenaccomplished, place the fertilizedeggs in a test tube filled with 10mL of seawater. Label your tubeand observe the eggs 24 hourslater under low power. Record anychanges that you see. CAUTION:Wash your hands immediatelyafter working with animals.


INVESTIGATEINVESTIGATE

1. Sperm are motile, thousandsare present on a slide, the sizeis close to 10 µm; eggs are notmotile, fewer than 100 on aslide, size is close to 150 µm.

2. Student answers may vary;fertilization is external, sochances of a sperm meetingan egg are less; a large num-ber of gametes releasedimproves the chances of fer-tilization.

3. Sperm tend to cluster aroundthe outer edge of the egg.

4. A fertilized egg forms a clearmembrane around the out-side edge of the egg shortlyafter fertilization.

Knowledge Have studentscorrelate their observations of seaurchin gametes with the patternseen throughout the animal king-dom. Is there that much variationbetween sperm and eggs of differ-ent species? Use the PerformanceTask Assessment List for MakingObservations and Inferences inPASC, p. 17. L2

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ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

801

Troubleshooting■ Some sea urchins may not

release gametes with the initialinjection. Repeat if necessary.

■ Make sure that you collect thesame number of syringes ashanded out.

Data and ObservationStudents will observe the differ-ences between egg and sperm.They will determine that devel-opmental changes occur withinminutes after fertilization.

Going FurtherGoing Further

Have students determine howlong sperm cells will remainalive (as judged by their motil-ity) after being released fromthe male sea urchin.

S ea urchins are typical of most echinoderms in thattheir sexes are separate, fertilization is external,

and development of a fertilized egg is quite rapid.Thus, these animals are excellent choices for studyinggametes, watching fertilization, and observingchanges occurring in a fertilized egg.


ProblemHow can you induce a sea urchin

to release its gametes?

Objectives In this BioLab, you will:■ Induce sea urchins to release their

gamete cells. ■ Observe living sperm and egg cells

under the microscope. ■ Observe developmental changes in

a fertilized sea urchin egg.

Materialslive sea urchins beakerssea water petri dishglass slides and dropper

cover slips microscopesyringe filled with test tube

potassium chloride

Safety PrecautionsAlways wear goggles in the lab.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

PREPARATIONPREPARATION

1. Fill a small beaker (250 mL) withsea water.

2. Obtain a live sea urchin fromyour teacher and locate an area ofsoft tissue next to its mouth.

3. Using a syringe, your teacher will insert the needle into thissoft tissue and inject the syringecontents into the sea urchin.

4. Turn your animal so that itsmouth is facing up and place it in a petri dish. CAUTION: Usecare in handling live animals.

5. Wait a minute or two, then check the petri dish. If the sea

urchin is male, a milky whitemass of sperm will be present inthe dish. If it is female, a yelloworange mass of eggs will be seen.

6. If you have a female sea urchin,hold her upside down directlyover the seawater-filled beakerand allow the eggs to fall directlyinto the water.

7. If your urchin is male, use a drop-per to add several drops of spermfrom the petri dish to your beakerof sea water.

8. Check with your classmates to seewho has a male and who has a

PROCEDUREPROCEDURE


Observing Sea Urchin Gametesand Egg Development

Red sea urchin


Time Allotment One class period the first day; 15minutes the second day

Process Skillsmake and use tables, collect data,communicate, compare and con-trast, measure in SI, observe andinfer, organize data, use numbers

Safety PrecautionsCaution students to use carewhen working with syringes andchemicals. Make sure they returnsyringes to the designated place.

Alternative Materials■ If time and cost prohibit the

purchase of live sea urchins,the experiment can be donewith prepared slides availablefrom biological supply houses.

PREPARATIONPREPARATION

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Teaching Strategies■ Student groups of at least four arerecommended. Each student should beassigned a specific duty or role.■ Sea urchins will typically arrive in alarge foam container and can remainthere for at least 24-48 hours before

using. Ordering so that animals arriveearly in the week is recommended.Animals are available from biologicalsupply houses.■ Use 2 mL of a 0.5M potassium chlo-ride (KCl) solution for each injection.■ The container in which the urchinsarrive will contain enough seawater forclassroom use.

■ To reduce the number of sea urchinsneeded, have the first morning class dothe injecting and capturing of gametes.Store sperm and eggs as follows for laterclasses: Cover petri dish with sperm,store in a refrigerator at 10ºC; storeeggs in beaker of seawater at same tem-perature as sperm. Try to use storedgametes the same day.

Fertilization membrane appears

First cleavage

Second cleavage

Third cleavage

Blastula

Gastrula

Larva

2-5 minutes

50-70 minutes

78-107 minutes

103-205 minutes

6 hours

12-20 hours

24-48 hours


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Chapter 29 AssessmentChapter 29 Assessment

SUMMARYSUMMARY

Section 29.1

Section 29.2

Main Ideas■ Echinoderms have spines or bumps on their

endoskeletons, radial symmetry, and water vas-cular systems. Most move by means of the suc-tion action of tube feet.

■ Echinoderms include sea stars, sea urchins, sanddollars, sea cucumbers, sea lilies, and featherstars.

■ Deuterostome development, an internal skele-ton, and bilaterally symmetrical larvae are indi-cators of the close phylogenetic relationshipbetween echinoderms and chordates.

Vocabularyampulla (p. 788)madreporite (p. 789)pedicellaria (p. 787)ray (p. 787)tube feet (p. 788)water vascular system

(p. 789)

Echinoderms

Main Ideas■ Chordates have a dorsal hollow nerve cord, a

notochord, muscle blocks, gill slits, and a tail atsome stage during development.

■ Sea squirts and lancelets areinvertebrate chordates.

■ Vertebrate chordates may have evolved from larval stagesof ancestral invertebrate chordates.

Vocabularydorsal hollow nerve

cord (p. 795)gill slit (p. 796)notochord (p. 795)

InvertebrateChordates

CHAPTER 29 ASSESSMENT 803

1. Sea stars, sea urchins, sand dollars, seacucumbers, sea lilies, and feather stars areexamples of echinoderms that all have________.a. exoskeletonsb. jointed appendagesc. tube feetd. larvae with radial symmetry

2. Of the following, which is NOT a character-istic of chordates?a. dorsal hollow nerve cordb. notochordc. pedicellariaed. muscle blocks

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS 3. When a sea star loses a ray, it is replaced bythe process of ________.a. regeneration c. metamorphosisb. reproduction d. parthenogenesis

4. Animals that have spines or bumps on theirendoskeletons, radial symmetry, and watervascular systems are ________.a. invertebrate chordatesb. chordatesc. vertebratesd. echinoderms

5. A close phylogenetic relationship betweenechinoderms and some chordates is indicatedby the fact that both have similar ________.a. habitats c. sizesb. larvae d. gills

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Main IdeasSummary statements can be used bystudents to review the major con-cepts of the chapter.

Using the VocabularyTo reinforce chapter vocabulary, usethe Content Mastery Booklet andthe activities in the Interactive Tutorfor Biology: The Dynamics of Life onthe Glencoe Science Web Site.www.glencoe.com/sec/science

1. c2. c3. a4. d5. b

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS


All ChapterAssessment

questions and answers have beenvalidated for accuracy and suitabil-ity by The Princeton Review.


Chapter Assessment, pp. 169-174MindJogger VideoquizzesComputer Test BankBDOL Interactive CD-ROM, Chapter 29

quiz

Many organisms use hydraulic systems to supplyfood and oxygen to, and remove wastes from, cellslying deep within the body. Hydraulics is a branch

of science that is concerned with the practicalapplications of liquids in motion. In living sys-

tems, hydraulics is usually concerned with the useof water to operate systems that help organisms

find food and move from place to place.

The sea star uses a unique hydraulic mechanismcalled the water vascular system for move-

ment and for obtaining food. The water vascularsystem provides the water pressure that operatesthe tube feet of sea stars and other echinoderms.

The water vascular system On the upper surface of a sea star is a sievelike disk, the madre-porite, which opens into a fluid-filled ring.Extending from the ring are long radial canalsrunning along a groove on the underside of eachof the sea star’s rays. Many small lateral canalsbranch off from the sides of the radial canals.Each lateral canal ends in a hollow tube foot.The tube foot has a small muscular bulb at oneend, the ampulla, and a short, thin-walled tube at the other end that is usually flattened into asucker. Each ray of the sea star has many tubefeet arranged in two or four rows on the bottomside of the ray. The tube feet are extended orretracted by hydraulic pressure in the water vas-cular system.

Mechanics of the water vascular system Theentire water vascular system is filled with waterand acts as a hydraulic system, allowing the seastar to move. The muscular ampulla contractsand relaxes with an action similar to the squeez-ing of a dropper bulb. When the muscles in thewall of the ampulla contract, a valve between thelateral canal and the ampulla closes so that waterdoes not flow backwards into the radial canal.The pressure from the walls of the ampulla acts

on the water, forcing it into the tube foot’s suckerend, causing it to extend.

When the extended tube foot touches a rockor a mollusk shell, the center of the foot isretracted slightly. This creates a vacuum,enabling the tube foot to adhere to the rock orshell. The tip of the tube foot also secretes asticky substance that helps it adhere. To moveforward, muscles in the ampulla relax, and mus-cles in the tube foot wall contract. These actionsshorten the tube foot and pull the sea star for-ward. Water is forced back into the relaxedampulla. When the muscles in the ampulla con-tract, the tube foot extends again. This pattern ofextension and retraction of tube feet results incontinuous movement. It is the coordinatedmovement of many tube feet that enable the seastar to move slowly along the ocean floor.


ConnectionPhysicsPhysics

Connection Hydraulics of Sea Stars

In what way do scallops and earthworms also usehydraulic pressure for locomotion?

To find out more about hydraulicpressure systems, visit the

Glencoe Science Web Site.www.glencoe.com/sec/science

CONNECTION TO BIOLOGYCONNECTION TO BIOLOGY

Sea star opening a mollusk to feed

802

Purpose Students learn the application ofphysical principles to biologicalsystems.

Teaching Strategies■ Have students refer to theInside Story of a sea star earlierin this chapter to see how thewater vascular system is con-nected to the ampullas and tubefeet.■ Explain that hydraulics is thepractical application of liquids inmotion and that in living systemsthe liquid is usually water. Theterm hydraulic means “operated,moved, or effected by water.”■ Have students discuss howflow of fluids in the body isessential to life. Topics mightinclude the delivery of oral med-ication, distribution of hormonessecreted by glands, or the re-moval of toxic substances in urine.

Connection to BiologyScallops take in water and thenclap their shells together, forcingwater out quickly to move theanimal in the opposite directionfrom the water flow. Earthwormshave a hydrostatic skeleton (rigid,water-filled coelom) that theirmuscles brace against for move-ment through the soil.

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ConnectionPhysicsPhysics

Connection


Note Internet addressesthat you find useful in

the space below for quick reference.

VIDEODISCThe Secret of LifeAction of Tube Feet

!7;FBD"

VIDEOTAPEMindJogger Videoquizzes

Chapter 29: Echinoderms and InvertebrateChordatesHave students work in groups as they playthe videoquiz game to review key chapterconcepts.




CHAPTER 29 ASSESSMENT 805

23. Relate the various functions of the water vas-cular system to the environment in whichechinoderms live.

24. How is the ability of echinoderms to regen-erate an adaptive advantage to these animals?

25. Explain how a sea squirt maintains homeosta-sis.

26. Observing and Inferring Explain why thetube feet of a sand dollar are located on itsupper surface as well as on its bottom surface.

27. Comparing and Contrasting Compare thepedicellariae of echinoderms with the nema-tocysts of cnidarians.

28. Concept Mapping Complete the conceptmap by using the following vocabulary terms:ampulla, madreporite, tube feet, water vascu-lar system.

THINKING CRITICALLYTHINKING CRITICALLY

ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

The diagrams below represent cross sectionsof larvae. The intestines are shown in redand the nerve cords are shown in blue.

Interpreting Scientific Illustrations Use thediagram to answer the following questions.1. Which of the diagrams shows a cross

section of a lancelet?a. Ab. Bc. Cd. none of the diagrams

2. Which of the diagrams would representsegmented worms and echinoderms?a. Ab. Bc. Cd. none of the diagrams

3. What does the yellow, solid area repre-sent?a. nerve cord c. notochordb. intestines d. spinal cord

4. What is wrong with diagram C if it rep-resents an invertebrate chordate?a. The notochord is ventral.b. The nerve cord is ventral and there is

no notochord.c. It is too flat.d. The intestine should be round.

5. Interpreting Scientific IllustrationsUsing the same color code and the samethree organs, draw a diagram of a crosssection of a larval sea squirt, sea star, and earthworm.

For additional review, use the assessmentoptions for this chapter found on the Biology: TheDynamics of Life Interactive CD-ROM and on theGlencoe Science Web Site.www.glencoe.com/sec/science

CD-ROM

echinoderms

All

a sievelike

have a

radial and lateral canals

connected to

4.

1.

that includes

2.

3.

AA BB CC

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23. Tube feet enable sea stars tomove and open bivalve mol-lusks for food. Tube feet arealso used for gas exchange andexcretion. This water vascularsystem works well in a waterenvironment.

24. Regeneration enables a sea starto survive and escape an attackby a predator. If a predatorbites off a ray, the sea star canescape while the predator isfeeding on that ray. A new raywill grow within weeks.

25. Sea squirts filter feed and takein oxygen from the water. Theymaintain a balance with theirwatery environment by filteringout what they require and giv-ing off wastes into the water.

26. The tube feet on the upper sur-face are modified to function asgills.

27. Pedicellariae of echinodermspinch potential predators butare not used in capturing preyand do not have immobilizingtoxins as do nematocysts.

28. 1. Water vascular system; 2.Ampulla; 3. Tube feet; 4.Madreporite

THINKING CRITICALLYTHINKING CRITICALLY


1. a2. b3. c4. b5. The sea squirt will look

like A, the sea star like B,and the earthworm like B.


6. Spines on sea stars and sea urchins are modi-fied into pedicellariae used for ________.a. feeding c. breathingb. protection d. reproduction

7. The water vascular system operates the tubefeet of sea stars and other echinoderms bymeans of ________.a. water pressure c. water pumps b. water exchange d. water filtering

8. Tube feet, in addition to functioning in loco-motion, also function in ________.a. gas exchange and digestionb. digestion and circulationc. gas exchange and excretiond. excretion and digestion

9. Water enters and leaves the water vascularsystem of a sea star through the ________.a. radial canal c. tube feetb. ampulla d. madreporite

10. Sea squirts and lancelets are invertebratechordates that have ________.a. pedicellariaeb. exoskeletonsc. tube feetd. larvae with bilateral symmetry

11. When a sea cucumber is threatened, it can________ its internal organs.

12. The ________ is a semirigid, rodlike structurecommon to all members of the phylumChordata.

13. When a sea star lifts up the tips of its rays, itis detecting ________.

14. Muscle blocks attached to the notochordenable chordates to be more ________.

15. Examine the diagram below. From whichgroup did brittle stars most likely evolve?

16. Tunicates and lancelets get food by ________.17. Most echinoderms flourished in the

Paleozoic era. Brittle stars require habitatsimilar to other echinoderms, but they didnot flourish during the Paleozoic becausethey most likely ________.

18. A ________ is a flat, disc-shaped echinodermwithout rays, and only minute hairlike spines.

19. Sea stars are more likely to leave a fossilrecord than ________ such as tunicates andlancelets.

20. The ________of this larva shows its close rela-tionship to chordates.

21. If you were an oyster farmer, why would yoube advised not to break apart and throw backany sea stars that were destroying the oysterbeds?

22. How does a sessile animal such as a sea squirtprotect itself?

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

804 CHAPTER 29 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

All or None When filling in answer ovals, remember to fill inthe whole oval. A computer will be scoring youranswers. Don’t give the right answer for a prob-lem only to lose points on it because the computercouldn’t read your oval.

804

6. b7. a8. c9. d

10. d11. release12. notochord 13. light or dark14. strong and flexible15. asteroids16. filter feeding17. evolved later18. sand dollar19. invertebrate chordates20. bilateral symmetry

21. Sea stars regenerate and thecut-up parts may become newsea stars.

22. Sea squirts are sessile, filterfeeders that can shoot jets ofwater to protect themselves.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS



RoundwormsRoundworms, phylum Nematoda, have a

pseudocoelom and a tubelike digestive systemwith two body openings. Most roundworms arefree-living, but many plants and animals areaffected by parasitic roundworms.

FlatwormsFlatworms, phylum Platyhelminthes, include

free-living planarians, parasitic tapeworms, andparasitic flukes. Flatworms are bilaterally symmet-rical animals with flattened solid bodies and nobody cavities. Flatworms have one body openingthrough which food enters and wastes leave.

Invertebrates

807

BIODIGESTBIODIGEST

Jellyfishes and othercnidarians have nemato-cysts on their tentacles.

Free-living flatworms have a head end with organs that sensethe environment. Flatworms candetect light, chemicals, food, andmovements in their surroundings.

Parasitic roundworms such asthis Trichinella are contractedby eating undercooked pork.Other roundworms can be con-tracted by walking barefoot oncontaminated soil.

Prey

Nematocyst VITAL STATISTICSVITAL STATISTICS

FlatwormsSize ranges: Largest, beef tapeworm,length, 30 mDistribution: Worldwide in soil, marine,brackish, and freshwater habitatsNumbers of species:Phylum Platyhelminthes:

Class Turbellaria—free-living planarians,3000 species

Class Cestoda—parasitic tapeworms, 3500 species

Class Trematoda—parasitic flukes, 8000 species

807

2 TeachActivity

Visual-Spatial Many of theinvertebrate phyla are best

observed in nature films. Selectseveral nature films that highlightinvertebrates. Ask students to listall the invertebrates they see inthe films, and group the animalsinto phyla. Ask them to identifythe characteristics they used toclassify the animals.

Visual LearningInterpersonal Ask studentgroups to make a labeled

diagram of a planarian worm onthe chalkboard. Ask them howthe shape of a planarian reflectsits living habits. Planarians areflattened, thereby enabling them toslip easily under rocks and debris instreams.

ActivityVisual-Spatial Provide stu-dents with binocular micro-

scopes, watch glasses, toothpicks,dropping pipettes, and a pla-narian worm culture. Ask them toplace a few drops of water in thewatch glass, then, using a tooth-pick, gently move a planarian tothe watch glass. Have studentsobserve the worm under themicroscope and describe itsmovement.

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BIODIGESTBIODIGEST

Direction ofwater flow

CnidariansLike sponges, cnidarians are made up of two

cell layers and have only one body opening. Thecell layers of a cnidarian, however, are organizedinto tissues with different functions. Cnidariansare named for stinging cells that contain nemato-cysts that are used to capture food. Jellyfishes,corals, sea anemones, and hydras belong to phy-lum Cnidaria.

806

InvertebratesHow are jellyfishes, earthworms, sea stars, and butterflies alike?

All of these animals are invertebrates—animals without back-bones. The ancestors of all modern invertebrates had simple bodyplans. They lived in water and obtained food, oxygen, and other mate-rials directly from their surroundings, just like present-day sponges,jellyfishes, and worms. Some invertebrates have external coveringssuch as shells and exoskeletons that provide protection and support.

For a preview of the invertebrate unit, study this BioDigest before you read the chapters.After you have studied the invertebrate chapters, you can use the BioDigest to review the unit.

BIODIGESTBIODIGEST

Sponges are filter feeders. A sponge takes inwater through pores in the sides of its body,filters out food, and releases the waterthrough the opening at the top.

VITAL STATISTICSVITAL STATISTICS

CnidariansSize ranges: Smallest: Haliclystus salpinx, jel-lyfish, diameter, 25 mm; largest: giant jellyfishmedusa, diameter, 2 m; largest coral colony:Great Barrier Reef, length, 2027 kmMost poisonous: The sting of an Australianbox jelly can kill a human within minutes.Distribution: Worldwide in marine, brackish,and freshwater habitats.Numbers of species:Phylum Cnidaria

Class Hydrozoa—hydroids, 2700 speciesClass Scyphozoa—jellyfishes, 200 speciesClass Anthozoa—sea anemones and corals,

6200 species

SpongesSponges, phylum Porifera, are invertebrates

made up of two cell layers. Most sponges areasymmetrical. They have no tissues, organs, ororgan systems. Most adult sponges do not movefrom place to place.

806

National Science Education Standards:UCP.1, UCP.2, UCP.5, C.1, C.4,C.5, C.6, F.1

PreparePurposeThis BioDigest can be used as anoverview of the invertebrate ani-mal phyla. You may wish to usethis unit summary to teach aboutinvertebrates in place of thechapters in the Invertebrate unit.

Key ConceptsStudents learn about the phyla ofinvertebrates, including sponges,cnidarians, flatworms, round-worms, arthropods, and echino-derms, as well as the invertebratechordates. They learn about cellorganization in animals andobserve differences in physicalforms as organisms become morecomplex, with cells organizedinto tissues, and tissues organizedinto organs and organ systems.

1 FocusBellringerBring an assortment of live inver-tebrates into the classroom andhave students examine them. Askstudents to identify traits thatthese animals share. They shoulddiscover that invertebrates areanimals without backbones.

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BIODIGESTBIODIGEST

MultipleLearningStyles

Look for the following logos for strategies that emphasize different learning modalities.

Kinesthetic Activity, p. 808;Meeting Individual Needs,

pp. 809, 810Visual-Spatial Activity, pp. 807,808, 809, 810, 811; Quick Demo,

pp. 810, 811Interpersonal Visual Learning,p. 807

Linguistic Biology Journal, p. 808Naturalist Visual Learning, p. 810; Check for Understand-

ing, p. 812


Exploration: The Five KingdomsDisc 3BioQuest: Biodiversity ParkDisc 3, 4Video: Ocean CnidariansDisc 4

Assessment PlannerAssessment Planner

Portfolio AssessmentAssessment, TWE, pp. 812, 813

Performance AssessmentBioDigest Assessment, TWE, p. 813

Knowledge AssessmentBioDigest Assessment, SE, p. 813

Skill AssessmentAssessment, TWE, p. 809

VIDEODISCThe Secret of LifeFlatworm Cross Section

!7;EtH"

Segmented WormsBristleworms, earthworms, and leeches are

members of phylum Annelida, the segmentedworms. Segmented worms are bilaterally symmet-rical, coelomate animals that have segmented,cylindrical bodies with two body openings. Mostannelids have setae, bristlelike hairs that extendfrom body segments, that help the worms move.

Segmentation is an adaptation that providesthese animals with great flexibility. Each segmenthas its own muscles. Groups of segments have dif-ferent functions, such as digestion or reproduction.

Classes of Segmented WormsPhylum Annelida has three classes: Hirudinae,

the leeches; Oligochaeta, the earthworms; andPolychaeta, the bristleworms.

Invertebrates

attachment of muscles,making movement moreefficient. Earthworms havea coelom, a body cavity sur-rounded by mesoderm inwhich internal organs aresuspended. The coelom actsas a watery skeleton againstwhich muscles can work.

809

BIODIGESTBIODIGEST

An acoelomateflatworm

A coelomatesegmented worm

A pseudocoelomate roundworm

Digestive tract

Most bristleworms have a distincthead and a body with many setae.

Leeches have flat-tened bodies withno setae. Mostspecies are parasitesthat suck blood andbody fluids fromducks, turtles, fishes,and mammals.


Segmented WormsSize ranges: Largest: giant tropical earth-worm, length, 4 m; smallest: freshwaterworm, Aeolosoma, length, 0.5 mmDistribution: Terrestrial and marine, brack-ish, and freshwater habitats worldwide,except polar regions and deserts.Numbers of species:Phylum Annelida

Class Hirudinea—leeches, 500 speciesClass Oligochaeta—earthworms,

3100 speciesClass Polychaeta—bristleworms,

8000 species

809

ActivityVisual-Spatial Give eachgroup of students a live

earthworm in one dish and abristleworm in another dish. Askthem to observe their behaviorand movements. Tell students tomake a table that shows the simi-larities and differences betweenearthworms and bristleworms.Earthworms may be obtainedfrom bait shops and bristlewormscan be obtained from biologicalsupply houses or bait shops nearthe sea.

Skill Ask students to findobjects in the room that havebilateral and radial symmetry. Askthem to explain why they haveidentified particular objects ashaving one type of symmetry oranother. Objects such as a penciland a test tube have radial sym-metry. If an object has radial sym-metry, it can be divided along anyplane through a central axis intoroughly equal halves. Objectssuch as books and chairs havebilateral symmetry. If an objecthas bilateral symmetry, it can bedivided along only one plane toform right and left halves that aremirror images. L2

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BIODIGESTBIODIGEST

MollusksSlugs, snails, clams, squids, and octopuses are

members of phylum Mollusca. All mollusks arebilaterally symmetrical and have a coelom, twobody openings, a muscular foot for movement,and a mantle, which is a thin membrane that sur-rounds the internal organs. In shelled mollusks,the mantle secretes the shell.

Classes of MollusksThe three major classes of mollusks are gas-

tropods with one shell or no shell; bivalves withtwo hinged shells; and cephalopods. Cephalopodsinclude octopuses, squids, and shelled nautilusesthat all have muscular tentacles and are capableof swimming by jet propulsion. All mollusks,except bivalves, have a rough, tongue-like organ called a radula usedfor obtaining food.

FOCUS ON ADAPTATIONSFOCUS ON ADAPTATIONS

The type of body cavity an ani-mal has determines how large

it can grow and how it takes in food and eliminates wastes. Acoelo-mate animals, such as planarians,have no body cavity. Water anddigested food particles travelthrough a solid body by the processof diffusion.

Animals such as roundwormshave a fluid-filled body cavity calleda pseudocoelom that is partly linedwith mesoderm. Mesoderm is a layerof cells between the ectoderm andendoderm that differentiates intomuscles, circulatory vessels, andreproductive organs. The pseudo-coelom provides support for the

Body Cavities

Invertebrates

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Gastropods, such as snails,use their radulas to scrapealgae from rock surfaces.


MollusksSize ranges: Largest: tropical giant clam,length, 1.5 m; North Atlantic giant squid,length, 18 m; Pacific giant octopus, length, 10m; smallest: seed clam, length, less than 1 mmDistribution: Worldwide in salt-, fresh-, andbrackish water, and on land in moist temper-ate and tropical habitats.Numbers of species:Phylum Mollusca

Class Gastropoda—snails and slugs, 80 000species

Class Bivalvia—bivalves, 10 000 speciesClass Cephalopoda—octopuses, squids, and

nautiluses, 600 species

Marine flatworm

Bivalves, such as clams,strain food from waterby filtering it throughtheir gills.

Cephalopods, such asoctopuses, are predators.They capture prey usingthe suckers on their longtentacles.

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ActivityVisual-Spatial Ask studentsto observe the movement of

a live land snail. As the snailmoves, ask students to describeits behavior when the antennaeare touched with a cotton swab.

Microscope ActivityAsk students to observe thedevelopment of snail eggs withhand lenses or binocular micro-scopes.

ActivityKinesthetic Ask students toset up a saltwater aquarium

and add marine mollusks that canbe obtained live from the super-market. Clams, mussels, and oys-ters are generally available. Havestudents care for and make obser-vations of their aquarium.P

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Invertebrate AdvertisementsLinguistic Ask students to prepare aclassified newspaper advertisement for

a homesite for three animals, one in each of the classes of mollusks. Provide studentswith a page of the real estate section of the

newspaper to review how such advertise-ments for homes are written. Studentsshould be creative with their language butkeep the precise habitat requirements ofeach animal in mind.

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MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

Visually ImpairedKinesthetic Provide poster boardcut-outs of flatworms, roundworms,

and segmented worms. Ask visually-impaired students to describe their tactileimpressions of each worm.

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Exploration: MollusksDisc 4

VIDEODISCThe Secret of LifeEarthworm

!7;F$A"

Arthropod OriginsArthropods most likely evolved from seg-

mented worms; they both show segmentation.However, an arthropod’s segments are fused and

have a greater complexity of structure than thoseof segmented worms. Because arthropods haveexoskeletons, fossil arthropods are frequentlyfound, and consequently more is known abouttheir origins than about the phylogeny of worms.

Invertebrates

Different Foods for Different Stages

Because insects undergo metamorphosis,they often utilize different food sources atdifferent times of the year. For example,monarch butterfly larvae feed on milkweedleaves, whereas the adults feed on milkweedflower nectar. Apple blossom weevil larvaefeed on the stamens and pistils of unopenedflower buds, but the adult weevils eat appleleaves. Some adult insects, such as mayflies,do not eat at all! Instead, they rely on foodstored in the larval stage for energy to mateand lay eggs. 811

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Mosquitomouthparts

Grasshoppermouthparts

Butterflymouthparts

Members of classInsecta, the insects,such as this lunamoth, have threepairs of jointed legsand one pair ofantennae for sensingtheir environments.

Millipedes, class Diplopoda, areherbivores. Millipedes have up to100 body segments, and each seg-ment has two pairs of legs.


ArthropodsSize ranges: Largest insects: tropical stickinsect, length, 33 cm; Goliath beetle, mass,100 g; smallest insect: fairyfly wasp, length,0.21 mmDistribution: All habitats worldwide.Numbers of species:Phylum Arthropoda

Class Arachnida—spiders and their rela-tives, 57 000 species

Class Crustacea—crabs, shrimps, lobsters,crayfishes, 35 000 species

Class Merostomata—horseshoe crabs, 4 species

Class Chilopoda—centipedes, 2500 speciesClass Diplopoda—millipedes,

10 000 speciesClass Insecta—insects, 750 000 species

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Visual LearningAsk students to examine thephoto of the moth and explainhow it is adapted to its way oflife. The color provides camouflagefrom predators. Large wings permitlong-distance flight while conservingenergy during the gliding parts ofthe flight. L1

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Visual-Spatial Provide stu-dents with a culture of

mealworms. Ask them to find andmake diagrams of the stages ofmetamorphosis they find in theculture.

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ArthropodsArthropods are bilaterally symmetrical, coelo-

mate invertebrates with tough outer coveringscalled exoskeletons and jointed appendages thatare used for walking, sensing, feeding, and mat-ing. Exoskeletons protect and support their softinternal tissues and organs. Jointed appendagesallow for powerful and efficient movements.

Arthropod DiversityTwo out of three animals on Earth today are

arthropods. The success of arthropods can beattributed to adaptations that provide efficientgas exchange, acute senses, and varied types of

mouthparts for feeding. Arthropods includeorganisms such as spiders, crabs, lobsters,shrimps, crayfishes, centipedes, millipedes,and the enormously diverse group ofinsects.

FOCUS ON ADAPTATIONSFOCUS ON ADAPTATIONS

Insects have many adaptations thathave led to their success in the air,

on land, in freshwater, and in saltwater. For example, insects havecomplex mouthparts that are welladapted for chewing, sucking, pierc-ing, biting, or lapping. Differentspecies have mouthparts adapted toeating a variety of foods.

If you have ever been bitten by amosquito, you know that mosquitoeshave piercing mouthparts that cut

through your skin to suck up blood.In contrast, butterflies and mothshave long, coiled tongues that theyextend deep into tubular flowers tosip nectar. Grasshoppers and manybeetles have hard, sharp mandiblesthey use to cut off and chew leaves.But the heavy mandibles of staghornbeetles no longer function as jaws;instead, they have become defensiveweapons used for competition andmating purposes.

Insects

Invertebrates

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The evolution of jointedappendages with many differentfunctions probably led to the suc-cess of the arthropods as a group.

Like other membersof class Arachnida,the black widow spider has four pairsof jointed legs and chelicerae, a pair of biting appendages nearthe mouth.

Staghorn beetle

Lobsters, class Crustacea, have antennae and two compound eyes on movable stalks. Theirmandibles move from side to side to seize prey.

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ActivityVisual-Spatial Ask studentsto bring in jars of many

types of arthropods. Number thejars and pass them from group togroup, asking students to writethe name of the arthropod andobvious arthropod features besidethe name. For each arthropod,ask them to infer what featureshelped to make that particulararthropod successful.

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Visual LearningNaturalist Ask students toexamine the diagrams of

arthropods on this page and iden-tify adaptations that enable eachanimal to survive in its habitat.

ActivityHave students design and con-duct an experiment to determinethe effect of temperature on thejumping ability of crickets.P

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Visual-Spatial Show stu-dents a live water strider

on the surface of pond water ina container with a large surfacearea. Ask students to hypothe-size how the water strider stayson top of the water. Ask themto identify adaptations the ani-mal has that enables it to skateon the water surface. L2

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Visual-Spatial Borrow a collection of preserved

butterflies from a nearby college or museum and call students’ attention to the enor-mous variety in wing shapes,sizes, and colors.

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P R O J E C THydraulics of Tube FeetHave students research the science ofhydraulics. Have them describe howhydraulics helps to operate the tube feetof echinoderms. Have them compare andcontrast this hydraulic system with otherhydraulic systems in the plant or animalkingdom. L3

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MMEETING EETING IINDIVIDUAL NDIVIDUAL NNEEDS EEDS MEETING INDIVIDUAL NEEDS

English Language LearnersKinesthetic For students who areEnglish language learners or are kines-

thetic learners, purchase plastic arthropods.Ask them to work in groups and point outfeatures of the arthropods as they pass themaround their group. Features that they might

be able to find include head, thorax, abdo-men, spiracles, claws, flippers, jointed legs,cephalothorax, antennae, mouthparts, pedi-palps, chelicerae, compound and simpleeyes, wings, tympanum, and mandibles.

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VIDEODISCThe Infinite VoyageInsects: The Ruling

Class, Insects and TheirBehavior (Ch. 1), 7 min.

Caterpillars: AlteringAppearances (Ch. 5), 5 min.

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CD-ROMBiology: The Dynamics of LifeExploration: Arthropods

Disc 4

Invertebrates

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The lancelet is anexample of aninvertebrate chor-date. Notice thatthe lancelet’s bodyis shaped like thatof a fish eventhough it is a burrowing filterfeeder.

BIODIGEST ASSESSMENTBIODIGEST ASSESSMENT

Understanding Main Ideas1. An animal that is a filter feeder, takes in

water through pores in the sides of itsbody, and releases water from the top is a________.a. roundworm c. spongeb. gastropod d. lancelet

2. Nematocysts are unique to ________.a. sponges c. annelidsb. mollusks d. cnidarians

3. An example of a free-living flatworm is a________.a. planarian c. nematodeb. tapeworm d. vinegar-eel

4. Which of the following is used by seg-mented worms for movement?a. cheliceraeb. nematocystsc. setaed. water vascular system

5. Which of the following are invertebratechordates?a. sea anemones c. bivalvesb. lancelets d. squid

6. Parasitism is a way of life for most________.a. flukes c. cnidariansb. sponges d. annelids

7. An example of an animal with no bodycavity is a(n) ________.a. sea star c. earthwormb. flatworm d. clam

8. An octopus belongs to phylum Molluscabecause it has a mantle, bilateral symme-try, two body openings, and ________.a. an external shellb. a muscular footc. a pseudocoelomd. segmentation

9. Leeches feed by ________.a. grazing on aquatic plantsb. stinging preyc. filter feedingd. sucking blood

10. Which of the following characteristics isunique to arthropods?a. nematocycts c. filter feedingb. jointed appendages d. tube feet

Thinking Critically1. A radula is to a snail as a(n) ________ is

to a jellyfish. Explain your answer.

2. Why is more known about animals withhard parts than is known about animalswith only soft parts?

3. In what ways are echinoderms more similar to vertebrates than to other inver-tebrates?

4. You are examining a free-living animalthat had a thin, solid body with two sur-faces. Into what phylum is this organismclassified? Explain.

5. In what two ways are spiders differentfrom insects?

a fluid-filled canal lying above the notochord. Gillslits are paired openings in the pharynx that, insome invertebrate chordates, are used to strainfood from the water. In other chordates, gill slitsdevelop into internal gills used for gas exchange.Muscle blocks are modified body segments con-sisting of stacked muscle layers. Muscle blocks areanchored by the notochord.

Invertebrate chordates have all of these fea-tures at some point in their life cycles. The inver-tebrate chordates include the lancelets and thetunicates, also known as sea squirts.

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ReteachAsk students to make a table inwhich they compare the charac-teristic features of invertebrateanimals.

ExtensionAsk students to make a collectionof local insects and identify thefeatures of these animals thatmake them adapted to the localenvironment.

Portfolio Using largeposter paper and markers, andtheir knowledge of invertebratestructure, have students design aninvertebrate that is adapted to liv-ing in the school parking lot. Askthem to make a diagram and a listof adaptations. Have studentsinclude their posters in their port-folios.

4 CloseActivityHave students conduct an inver-tebrate survey of a nearby pond,meadow, wetland, or woodland.If time permits, ask them to com-pare the types of invertebratesfound in different habitats.

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EchinodermsEchinoderms, phylum Echinodermata, are

radially symmetrical, coelomate animals withhard, bumpy, spiny endoskeletons covered by thinepidermis. The endoskeleton is comprised of cal-cium carbonate. Echinoderms move using aunique water vascular system with tiny, suction-cuplike tube feet. Some echinoderms have longspines also used in locomotion.

Echinoderm DiversityThere are five major classes of echinoderms.

They include sea stars, brittle stars, sea urchins,sea cucumbers, sand dollars, sea lilies, and featherstars.

Echinoderms have bilaterally symmetrical lar-vae, a feature that suggests a close relationship tothe chordates.

Invertebrate ChordatesAll chordates have, at one stage of their life

cycles, a notochord, a dorsal hollow nerve cord,gill slits, and muscle blocks. A notochord is a long,semirigid, rodlike structure along the dorsal sideof these animals. The dorsal hollow nerve cord is

Invertebrates

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The tube feet of a sea star operateby means of a hydraulic water vas-

cular system. Sea stars movealong slowly by alternately

pushing out and pullingin their tube feet.

Sea cucumbers have aleathery skin and areflexible. Like mostechinoderms, theymove using tube feet.


EchinodermsSize ranges: Largest: sea urchin, diameter,19 cm; longest: sea cucumber, length, 60 cmDistribution: Marine habitats worldwide.Numbers of species:Phylum Echinodermata

Class Asteroidea—sea stars, 1500 speciesClass Crinoidea—sea lilies and feather

stars, 600 speciesClass Ophiuroidea—brittle stars,

2000 speciesClass Echinoidea—sea urchins and sand

dollars, 950 speciesClass Holothuroidea—sea cucumbers,

1500 species

The long, thin arms of brittle stars are fragile and break easily, but they grow back. Brittlestars use their arms to walkalong the ocean bottom.

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Portfolio Have studentsvisit a local zoo or pet shop thatmaintains a saltwater aquarium.Have them time their visit so theyare present when it is feedingtime for echinoderms such as seastars, brittle stars, and featherstars. Have students watch oneechinoderm as it feeds, thendescribe the behavior of the ani-mal in their portfolios.


3 AssessCheck for Understanding

Naturalist Set up a lab prac-tical with stations with pre-

served or live invertebrates. Askstudents to identify the phylumand group within the phylum towhich each animal belongs, andexplain the visible features thathelped them classify the inverte-brates. L2

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Note Internet addresses that you find useful in the spacebelow for quick reference.


Content Mastery, pp. 145-148

Reinforcement and StudyGuide, pp. 131-132 L2

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BIODIGEST ASSESSMENTBIODIGEST ASSESSMENT

Understanding Main Ideas1. c 4. c 7. b 10. b2. d 5. b 8. b3. a 6. a 9. d

Thinking Critically1. nematocyst; a snail obtains food with its

radula; a jellyfish obtains its food with

nematocysts2. Hard parts leave fossil evidence while soft

parts leave little fossil evidence.3. Echinoderms have bilaterally symmetrical

larvae, as do chordates.4. It belongs to the phylum Platyhelminthes

because it is a free-living flatworm.5. Spiders have four pairs of legs; insects have

three. Spiders have chelicerae; insects havemany different types of mouthparts. Insectshave antennae; spiders do not.


Exploration: EchinodermsDisc 4

Chapter 29: Echinoderms and Invertebrate Chordates

Documents

Transcript of Chapter 29: Echinoderms and Invertebrate Chordates