CHAPTER

36 ARTHROPODSPlanning Guide

Compression GuideTo shorten instructionbecause of time limitations,omit Section 3.

Chapter Opener

Section 1 Phylum Arthropoda• Describe the distinguishing characteristics of arthropods.• Explain the process of molting in an arthropod.• List the four major subphyla of the phylum Arthropoda.

Section 2 Subphylum Crustacea• Describe the characteristics of crustaceans. • Compare aquatic crustaceans with terrestrial

crustaceans. • Explain the functions of the appendages on a crayfish.• Summarize digestion, respiration, circulation, excretion,

and neural control in crayfish.

TE Demonstration Tailflip Behavior, p. 726 ◆bTE Activity Observing Crustaceans, p. 727 ◆gTE Demonstration Horseshoe Crabs, p. 729 ◆bTE Internet Activity Crustaceans, p. 729 gSE Quick Lab Observing Crayfish Behavior,

p. 730 ◆gANC Datasheets for In-Text Labs Observing Crayfish

Behavior*gSE Inquiry Lab Investigating Pill Bug Behavior,

pp. 738–739 ◆gANC Datasheets for In-Text Labs Investigating Pill Bug

Behavior*gHBS Quick, Data, and Math Labs Relating Molting to

Mortality Rates*gHBS Skills Practice Labs Crayfish Dissection* ◆g

TE Activity Spider Anatomy, p. 731 ◆bTE Internet Activity Archnida, p. 732 gTE Group Activity Arthropod Identification,

p. 733 ◆gTE Demonstration Myriapods, p. 734 ◆b

OSP Parent LetterCD Student Edition on CD-ROMCD Guided Reading Audio CD

TR H26 Characteristics of Arthropods*TR H27 Phylogenetic Diagram of

Arthropods*CD Visual Concepts CD-ROM

TR H28 External Anatomy of a Crayfish*TR H29 Internal Anatomy of a Crayfish*CD Visual Concepts CD-ROMVID Biology Lab Video Observing Pill

Bug BehaviorCD Virtual Investigations Respiration

in Invertebrates

TR H30 Anatomy of a Brown Recluse Spider*

CD Visual Concepts CD-ROM

pp. 722–725

722A C H A P T E R 3 6 A r t h r o p o d s

OBJECTIVES LABS, DEMONSTRATIONS, AND ACTIVITIES TECHNOLOGY RESOURCESPACING • 45 min

pp. 726–730PACING • 90 min

pp. 731–734PACING • 45 minSection 3 Subphyla Chelicerata and Myriapoda• List the characteristics of arachnids, as represented by

a spider.• Explain the adaptations that spiders have for a predatory

life on land.• Identify the unique characteristics of scorpions, mites,

and ticks.• Compare the characteristics of millipedes and

centipedes.

TE Internet Activity Arthropods, p. 724 gHBS Quick, Data, and Math Labs Evaluating Jointed

Appendages*gHBS Quick, Data, and Math Labs Comparing

Arthropods* ◆g

SE Chapter Highlights, p. 735SE Chapter Review, p. 736TR Graphic Organizer*gTR Concept Mapping*g

ANC Vocabulary Review*gANC Quizzes*gANC Chapter Test*gANC Chapter Test*a

SE Standardized Test Prep, p. 737OSP Test GeneratorOSP Test Item Listing

CHAPTER REVIEW, ASSESSMENT, ANDSTANDARDIZED TEST PREPARATION

PACING • 90 min

Visit go.hrw.com to find avariety of online resources.Click Holt Online Learningfor an online edition of this textbook and otherinteractive resources.

This DVD package includes: • Holt Calendar Planner• Customizable Lesson Plans• Editable Worksheets• MindPoint® Quiz Show• Holt PowerPoint® Resources

• ExamView® Version 6.0Assessment Suite

• Interactive Teacher’s Edition• Holt PuzzlePro®

Online and Technology Resources

KEY SE Student Edition OSP One-Stop Planner VID Classroom Video/DVDTE Teacher Edition TR Transparencies and * Also on One-Stop Planner

ANC Ancillary Workbook Transparency Worksheets ◆ Requires advance prepHBS Holt BioSources Lab Program CD CD or CD-ROM

TE Using the Figure Exoskeletons, p. 722ANC Science Skills Worksheet*gANC Critical Thinking Worksheet*a

TE Reading Skill Builder Interactive Reading, p. 723 bTE Skill Builder Writing Skills, p. 724 aTE Using the Figure Phylogenetic Diagrams, p. 725 b

ANC Active Reading Guide*

TE Reading Skill Builder Reading Organizer, p. 727 bTE Using the Figure Barnacles, p. 727 gTE Using the Table Crayfish Appendages, p. 728 bTE Skill Builder Science Literacy, p. 729 a

ANC Active Reading Guide*

TE Skill Builder Writing Skills, p. 732 aTE Inclusion Strategies, p. 732 ◆TE Inclusion Strategies, p. 733 ◆

ANC Active Reading Guide*

TE Assessing Prior Knowledge, p. 722ANC Study Guide*g

SE Section Review, p. 725 gTE Reteaching, p. 725 ◆bTE Quiz, p. 725 g

SE Section Review, p. 730 gTE Reteaching, p. 730 bTE Quiz, p. 730 g

SE Section Review, p. 734 gTE Reteaching, p. 734 bTE Quiz, p. 734 gTE Alternative Assessment, p. 735 gTE Study Tip, p. 735 g

National Science EducationStandards

LSCell1, LSCell2, LSCell4, LSEvol1,LSEvol5, LSMat4, LSBeh2, UCP1,UCP2, UCP4, UCP5, HNS2

LSEvol1, LSEvol5, LSMat4, LSBeh2, UCP1, UCP2, UCP4, UCP5,SI1, SI2, HNS2

LSEvol1, LSEvol5, LSMat4, LSBeh2, UCP1, UCP2, UCP4, UCP5,HNS2

C H A P T E R 3 6 P l a n n i n g G u i d e 722B

SKILLS DEVELOPMENT RESOURCES REVIEW AND ASSESSMENT CORRELATIONS

Maintained by the National ScienceTeachers Association.

www.scilinks.orgClassroom CD-ROMs

• Guided Reading Audio Program• Student One Stop• Virtual Investigations• Visual Concepts• Dissection Labs

Classroom Videos

• Lab Videos demonstratethe chapter lab.

Holt Lab GeneratorCD-ROM

Search for any lab by topic, standard,difficulty level, or time. Edit any lab to fit your needs, or create your own labs.Use the Lab Materials QuickList softwareto customize your lab materials list.

722 C H A P T E R 3 6

CHAPTER 36Using the FigureExoskeletons Having an exo-skeleton has contributed to thesuccess of arthropods. Ask stu-dents to look at the crustacean inthe photograph and to think ofsome advantages and disadvan-tages of having an exoskeleton.(An exoskeleton offers protection frompredators, disease, and dehydration.However, an arthropod must shed itsexoskeleton to grow, and that makes itvulnerable to predators until the newexoskeleton hardens.) Visual

Assessing PriorKnowledgeReview the following conceptswith students.

Exoskeleton (Ch. 32): Ask stu-dents to distinguish between anendoskeleton and an exoskeleton.(endoskeleton: internal framework that supports and protects the body;exoskeleton: external framework thatsupports and protects the body)

Segmentation (Ch. 35): Ask students to name a phylum ofworms with segmented bodiesand to explain the advantages ofsegmentation. (Annelida; segmenta-tion allows different parts of the body tobe specialized and function somewhatindependently. Some organ systems are duplicated, thus the organism canfunction if one segment is disabled.)

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National Science Education Standards

LSCell1 Cells have particular structures that underlie their functions.

LSCell2 Most cell functions involve chemical reactions.

LSCell4 Cell functions are regulated.

LSEvol1 Species evolve over time.

LSEvol5 Biological classifications are based on how organisms are related.

LSMat4 The complexity and organization of organismsaccommodates the need for obtaining, transforming,

transporting, releasing, and eliminating the matter and energy used to sustain the organism.

LSBeh2 Organisms have behavioral responses to internalchanges and to external stimuli.

UCP1 Systems, order, and organization

UCP2 Evidence, models, and explanation

UCP3 Change, constancy, and measurement

UCP5 Form and function

ST1 Abilities of technological design

ST2 Understandings about science and technology

The jointed appendages andhard exoskeleton of this red reeflobster, Enoplometopus occidentalis,are characteristic of arthropods.

SECTION 1 Phylum Arthropoda

SECTION 2 Subphylum Crustacea

SECTION 3 Subphyla Chelicerata and Myriapoda

36CHAPTER ARTHROPODSARTHROPODS

Biology Virtual InvestigationsRespiration in Invertebrates

Dissection LabsCrayfish

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OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describesthe trends in arthropod evolutionand briefly describes the differ-ences between the five subphylaof arthropods.

Bring in the exoskeleton of a lobster, crab, tarantula, or otherarthropod. Allow students toexamine it with a hand lens andtry to find the areas where mus-cles were attached to the interiorsurface. Visual

DiscussionJointed Appendages Tell studentsthat jointed appendages were amajor evolutionary development.Ask them how life would be differ-ent without one particular joint,such as the thumb joint. (It wouldbe difficult to hold a pen, fork, pick upobjects, even type at a computer key-board.) Lead them in a discussionof how different life would bewithout major joints in the arms,legs, and head. You might havethem think about animals thathave both greater (owl’s head)and lesser (lobster’s head) degreesof mobility of a body part thanhumans. (Owls can remain nearlymotionless while turning their heads 180 degrees to scan for prey. Lobstershave stalked eyes for scanning the environment, but must otherwise movetheir entire bodies. Humans can see to either side but not behind withoutturning the body.) Verbal

Interactive Reading AssignChapter 36 of the Modern BiologyGuided Reading Audio CDProgram to help studentsachieve greater success in reading the chapter.

VerbalLS

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SECTION 1

PH Y L UM A R T H RO P O DATwo-thirds of all animal species belong to the phylum

Arthropoda (ahr-THRAHP-uh-duh). This phylum contains a

variety of bilaterally symmetrical coelomates, including lobsters,

crabs, spiders, and insects. These animals have adapted to

almost every environment on Earth.

CHARACTERISTICS OFARTHROPODS

The members of the phylum Arthropoda are called arthropods(AHR-thruh-PAHDS). Like annelids, arthropods are segmented animals.In arthropods, however, the body segments bear jointed exten-sions called appendages, such as legs and antennae. In fact, arthro-pod means “jointed foot.”

Another distinguishing feature of arthropods is their exoskele-ton, which provides protection and support. As Figure 36-1shows, the arthropod exoskeleton is made up of three layers thatare secreted by the epidermis, which lies just beneath the layers.The waxy outer layer is composed of a mixture of protein andlipid. It repels water and helps keep terrestrial arthropods fromdrying out. The middle layer, which provides the primary protec-tion, is made mainly of protein and chitin, a tough polysaccha-ride. In some arthropods, the middle layer is hardened by theaddition of calcium carbonate. The inner layer also contains pro-tein and chitin, but its flexibility at the joints allows arthropodsto move freely. Muscles that attach to the inner layer on eitherside of the joints move the body segments.

Arthropods show a high degree of cephalization. Recall thatcephalization is the concentration of sensory and brain structuresat the anterior end. A variety of segmented appendages around themouth serve as sensors and food handlers. Most arthropods havesegmented antennae that are specialized for detecting chemicals.Most arthropods also have compound eyes—eyes made of manyindividual light detectors, each with its own lens. In addition, manyarthropods have simpler structures that sense light intensity.These sensory structures on the head send nerve impulses to thebrain, which coordinates the animal’s actions. As in annelids,impulses travel from the brain along a ventral nerve cord, whichlinks ganglia in the other segments of the body.

All arthropods have open circulatory systems. Recall that in anopen circulatory system, the heart pumps circulatory fluidthrough vessels that empty into spaces in the body.

SECTION 1

O B J E C T I V E S

● Describe the distinguishing characteristics of arthropods.

● Explain the process of molting in an arthropod.

● List the five major subphyla of thephylum Arthropoda.

V O C A B U L A R Y

arthropodappendagechitincompound eyemoltingtrilobite tagmamandiblechelicera

Sensory hair

Outerlayer

MiddlelayerInnerlayer

Epidermis

Wax gland

The arthropod exoskeleton consists ofthree layers that cover the epidermis.Wax in the outer layer is secreted bywax glands. Sensory hairs projectingfrom the exoskeleton allow arthropodsto respond to vibrations and chemicalsin their environment.

FIGURE 36-1

723

STATE RESOURCES

For specific resourcesfor your state, visitgo.hrw.com and type inthe keyword HSHSTR.

TEACHER RESOURCES

Workbooks

Active Reading Guide (Section 1)

Technology

Transparencies• H26 Characteristics of Arthropods

Visual Concepts CD-ROM• Types of Arthropods, Characteristics of Arthropods,

Segmentation, Compound Eye, Function of theCompound Eye

Teaching TipExoskeleton Molt Look for dis-carded arthropod exoskeletonsaround the school or at home,and bring them to class. Point outthe area along the dorsal surfaceof the exoskeleton where the animal emerged during molting.Ask students to note that theexoskeleton covered the entiresurface of the animal, includingthe legs, mouthparts, antennae (if present), and eyes. Have stu-dents observe the light weight ofthe exoskeleton, and explain thatarthropods reabsorb part of theold exoskeleton before they molt.

Visual

Writing Skills Have studentsinvestigate the hormones involvedin molting in arthropods. Thesehormones include ecdysone,which stimulates molting; brainhormone, which triggers therelease of ecdysone; and bursicon,which causes the new exoskeletonto harden. Ask students to focuson where these hormones areproduced and what effects theyhave on arthropod tissues.

Verbal

Arthropods Have studentsresearch the significance ofarthropods in the environment byusing the Internet Connect boxon this page. IntrapersonalLS

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724 C H A P T E R 3 6

MoltingA rigid exoskeleton limits the size to which an arthropod can grow.So, each arthropod periodically sheds its exoskeleton and makes anew one in the process of molting. An anthropod goes throughmany cycles of molting during its life. Figure 36-2 shows an insectin the process of molting.

A cycle of molting begins as the tissues of an arthropod gradu-ally swell. When the pressure inside the exoskeleton is very strong,a hormone that triggers molting is produced. In response to thishormone, the cells of the epidermis secrete enzymes that digestthe inner layer of the exoskeleton. At the same time, the epidermisbegins to make a new exoskeleton by using the digested material.Eventually, the outer layer of the old exoskeleton loosens, breaksapart, and is shed. The new exoskeleton, which is flexible at first,stretches to fit the enlarged animal.

The new exoskeleton takes a few hours to a few days to becomeas hard as the one that it replaced. During this time, the animal isvulnerable to predators and, if the arthropod is terrestrial, to des-iccation. For these reasons, arthropods usually stay in hiding fromthe time that they begin to molt until their new exoskeleton hashardened. The “soft-shelled crabs” sold in some restaurants arecrabs that have been caught immediately after molting.

EVOLUTION ANDCLASSIFICATION

Animals having arthropod characteristics first appeared about545 million years ago. Because all arthropods have a true coelom,an exoskeleton, and jointed appendages, biologists infer that allarthropods evolved from a common ancestor. However, biologistsare still uncertain about the order in which subgroups of arthro-pods evolved and the exact relationships between the subgroups.The phylogenetic diagram in Figure 36-3 shows possible evolution-ary relationships between the highly diverse arthropod subgroups.

The similar characteristics of many modern subgroups of arthro-pods may be the result of convergent evolution. For example, ancientand extinct arthropods, such as trilobites, had many body segmentsand one pair of appendages on each segment. However, most livingarthropod species have some segments that lack appendages andsome segments that are fused into a larger structure called a tagma(plural, tagmata). The tagmata tend to be specialized for functionssuch as feeding, locomotion, and reproduction.

Arthropods are usually divided into five subphyla on the basis ofdifferences in development and in the structure of appendages, suchas mouthparts. The two major types of mouthparts are mandibles,which are jawlike, and chelicerae (singular, chelicera), which are pin-cerlike. The five main subphyla are Trilobita, Crustacea, Chelicerata,Myriapoda, and Hexapoda, as Figure 36-3 shows.

This green cicada, Tibicen superbus, is inthe process of molting. The outer layerof its old exoskeleton appears brown.

FIGURE 36-2

chelicera

from the Greek chele, meaning“claw,” and keras, meaning “horn”

Word Roots and Origins

www.scilinks.org

Topic: ArthropodsKeyword: HM60098

724

CHEMISTRYCHEMISTRYCONNECTIONCONNECTION

Organic Compounds The hydrophobicnature of lipids gives the outer layer of theexoskeleton its water repellency. Chitin, amajor component of the middle and innerlayers, is a leathery polysaccharide.

TEACHER RESOURCES

Workbooks

Quick, Data, and Math Labs• Evaluating Jointed Appendages• Comparing Arthropods

Technology

Transparencies• H27 Phylogenetic Diagram of Arthropods

Visual Concepts CD-ROM• Arthropod Exoskeleton

GENERAL

GENERAL

Using the FigurePhylogenetic Diagrams Explainthat organisms on one branch of the phylogenetic diagram inFigure 36-3 are more closelyrelated to each other than toorganisms on other branches. For example, millipedes are moreclosely related to centipedes than to insects. Visual

ReteachingClassifying Arthropods Presentstudents with photographs of vari-ous types of arthropods and askthe students to name the subphy-lum to which each arthropodbelongs. If key features, such asmouthparts and other appendages,are not visible, add a legend tothe photograph describing thosefeatures. Ask students to explainwhy they assigned each photo-graph to a particular subphylum.

Visual

QuizTrue or False:1.When an arthropod molts, it

sheds only its epidermal layer.(false, enzymes from the epidermisdigest the inner layer of the oldexoskeleton and makes a newexoskeleton, the outer layer of the old exoskeleton is shed)

2.Tagmata are fused body segments. (true)

3.Mandibles are jawlike mouth-parts. (true)

4.Chelicerae are jawlike mouth-parts. (false, chelicerae are pincer-like mouthparts)

5.Trilobites are extinct arthropods. (true)

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A R T H R O P O D S 725

1. What characteristics do all arthropods share?

2. What is the main function of each layer of anarthropod’s exoskeleton?

3. What is a compound eye?

4. What is molting?

5. Identify the difference between chelicerae andmandibles.

6. Identify examples of organisms in each of thefive main subphyla of arthropods.

CRITICAL THINKING

7. Inferring Relationships What is the adaptiveadvantage of having a layered exoskeleton?

8. Analyzing Concepts After its old exoskeletonhas been shed but before the new one has hard-ened, an aquatic arthropod absorbs water andswells. How is this behavior adaptive?

9. Interpreting Graphics Study Figure 36-3. Arepill bugs more closely related to centipedes orto barnacles? Explain your answer.

SECTION 1 REVIEW

PhylumArthropoda

Chelicerata

Crustacea

Trilobita Trilobita(trilobites)extinct

Eurypterida(sea scorpions)extinct

Xiphosura(horseshoe crabs)

Scorpiones(scorpions)

Acari(ticks, mites)

Araneae(spiders)

Branchiopoda(brine shrimp, fairy shrimp, water fleas)

Pantopoda(sea spiders)

Thecostraca(barnacles and relatives)

Copepoda(copepods, sea lice)

Ostracoda(ostracods, seed shrimp)

Isopoda(pill bugs, sow bugs)

Decapoda(shrimp, crabs, lobsters)

Chilopoda(centipedes)

Diplopoda(millipedes)

Entognatha(springtails, proturans,and diplurans)

Insecta(insects)

Pycnogonida

Merostomata

Arachnida

Maxillopoda

Malacostraca

CH

ELIC

ER

ATE

S (having

chelicerae)M

AN

DIB

ULAT

ES

(having m

andib

les)

Myriapoda

Hexapoda

This phylogenetic diagram showshypotheses of the evolutionaryrelationships between the highlydiverse arthropod subgroups.Dashed lines indicaterelationships that are poorlyunderstood or that are heavilydebated. For updates onphylogenetic information, visitgo.hrw.com and enter thekeyword HM6 Phylo.

FIGURE 36-3

725

Answers to Section Review

1. true coelom, segmented body, jointed appendages,exoskeleton, cephalization, ventral nerve cord, andopen circulatory system.

2. outer layer: repels water and helps prevent desic-cation, middle layer: provides the primary protec-tion, inner layer: provides flexibility at the joints

3. an eye composed of many individual light detec-tors, each with its own lens

4. the process by which an arthropod sheds itsexoskeleton and develops a new one

5. Mandibles are jawlike mouthparts, and cheliceraeare pincerlike mouthparts.

6. Trilobita: trilobites, Chelicerata: sea spider, seascorpions, horseshoe crabs, scorpions, ticks,

mites, or spiders, Crustacea: brine shrimp, fairyshrimp, water fleas, copepods, barnacles, pill bugs,shrimp, crabs and lobsters, Myriapoda: centipedes,or millipedes, Hexapoda: springtails, proturans,diplurans, or insects

7. Sample answer: Each layer can adapt to fit theneeds of the organism, which allows for protection,strength, and flexibility in each layer.

8. Swelling expands the new exoskeleton before ithardens, allowing room for the animal’s growthbefore the next molt.

9. Sample answer: Pill bugs are more closely relatedto barnacles than to centipedes. Pill bugs and barnacles share a common branch on the phylo-genetic diagram that centipedes do not share.

OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describesthe organization of the crustaceanbody into digestive, respiratory,circulatory, excretory, and nervoussystems, using the crayfish as arepresentative example.

Invite students to name as manycrustaceans as they can. If theyhave difficulty, suggest that theythink about crustaceans they mayhave seen in seafood restaurantsand aquaria. (Students are probablyfamiliar with lobsters, shrimp, crabs,barnacles, and pill bugs.) Logical

DemonstrationTailflip Behavior Bring in a fewcrayfish in a bucket for studentsto observe. Have students predicthow the crayfish will move if astick is suddenly placed in front ofthem. Students may be surprisedwhen the crayfish shoots off back-ward in a motion known as a tail-flip. Have students observe thecrayfish’s movement for severalminutes. Visual LS

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Trends in NeurophysiologyCrayfish Behavior Research has shown that serotonin, a chemical produced by thecrayfish nervous system, influences tailflipbehavior in ways that depend on the socialstatus of a crayfish. Serotonin apparentlylowers the stimulus threshold needed to trig-ger a tailflip in dominant individuals but raisesthe threshold in subordinate individuals.

726 C H A P T E R 3 6

S U B P H Y L UM C R U S T A C E AThe subphylum Crustacea contains about 38,000 known

species. Crustaceans are abundant in oceans, lakes, and

rivers, and a few species live on land. Some crustaceans are

sessile, while others move by walking on legs, swimming with

paddle-like appendages, or drifting with the currents.

CHARACTERISTICSCrustaceans are so diverse that their single defining characteristicis having two pairs of antennae. Also, most crustaceans have a pairof jawlike, chewing mouthparts called mandibles. In most crus-taceans, each body segment has a pair of appendages, and at leastsome of those appendages are branched. Although some crus-taceans have 60 or more body segments, most crustaceans have 16to 20 segments, which are fused into several tagmata.

Some small crustaceans, such as pill bugs, respire through thethin areas of their exoskeleton. Larger crustaceans, such as cray-fish and lobsters, use gills to respire. The exoskeletons of aquaticcrustaceans, such as lobsters, often contain large amounts of cal-cium carbonate and thus are extremely hard.

During the development of many crustaceans, the embryobecomes a free-swimming larva called a nauplius (NAH-plee-uhs),which looks quite different from an adult of the species. As Figure36-4 shows, a nauplius has three pairs of appendages and a singleeye in the middle of its head. Through a series of molts, the nau-plius eventually takes on the adult form.

DIVERSITY OFCRUSTACEANS

Crustaceans exist in a range ofsizes, but most are small. Forexample, copepods (KOH-puh-PAHDZ),as shown in Figure 36-5a, are nolarger than the comma in this sen-tence. At the other end of the sizespectrum is the Japanese spidercrab, shown in Figure 36-5b. With aleg span of 4 m (13 ft), this crab isthe largest living arthropod.

SECTION 2

O B J E C T I V E S

● Describe the characteristics ofcrustaceans.

● Compare aquatic crustaceans withterrestrial crustaceans.

● Explain the functions of theappendages on a crayfish.

● Summarize digestion, respiration,circulation, excretion, and neuralcontrol in crayfish.

V O C A B U L A R Y

naupliuscirrusisopoddecapodcephalothoraxthoraxcarapaceabdomenantennaantennulechelipedswimmerettelsonuropoddigestive glandgreen gland

EyeAppendages

The free-swimming nauplius is an early stage in the development of most crustaceans. It has one eye and three pairs of appendages.

FIGURE 36-4

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SECTION 2

TEACHER RESOURCES

Workbooks

Active Reading Guide (Section 2)

Technology

One-Stop Planner CD-ROM• Occupational Application Worksheets

Biology Teacher

Visual Concepts CD-ROM• Characteristics of Crustaceans, Anatomy of a

Nauplius, Arthropod Exoskeleton

DiscussionHermit Crabs Hermit crabs livewith their abdomen coiled upinside a discarded snail shell.What problem does this lifestylecreate as far as the crab’s growthis concerned? (For a hermit crab togrow, it must find a larger snail shellto inhabit.) Logical

Reading Organizer As studentsread this section, have them putthe various external and internalstructures of a crayfish on indexcards. The name of the structureshould be placed on one side,and its description on the other.Encourage English languagelearners to write the structureand description in both Englishand their native language. Havestudents use the cards as flashcards to review the section. Tellthem to save their cards for theReteaching activity at the end ofthe section.

Verbal

ActivityObserving Crustaceans Havestudents use a microscope toobserve small crustaceans inwater collected from a local pond.Ask them to look for organismsthat seem to have complex bodyorgans and resemble shrimp orcrabs. Examples they might findare Cyclops, water fleas (Daphnia),and seed shrimp. Have studentsdraw the crustaceans they find anduse guide books to identify them.

Visual

Using the FigureBarnacles At first glance, a barnacle, such as the one inFigure 36-6, may look like a mollusk. However, a barnacle’sjointed cirri and internal anatomyindicate that it is a crustacean.Ask students to name some ani-mals they have encountered inearlier chapters whose lifestyleand feeding habits resemblethose of barnacles. (sponges andmost bivalve mollusks) Visual LS

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(a) Copepod, Cyclops sp. (c) Goose barnacle, Lepas anatifera(b) Japanese spider crab, Macrocheira kaempferi

Crustaceans include tiny species, such as the copepod (a), as well as giantspecies, such as the Japanese spidercrab (b). Some aquatic species, such asbarnacles (c), attach themselves tosubmerged marine surfaces.

FIGURE 36-5Aquatic CrustaceansCopepods are extremely abundant in marine environments andmay be the most abundant animals in the world. Copepods are animportant part of the ocean’s plankton, the collection of smallorganisms that drift or swim weakly near the surface of the water.

In freshwater environments, on the other hand, much of theplankton is composed of crustaceans known as water fleas, whichare about the size of copepods. A common type of water flea is amember of the genus Daphnia.

Barnacles, such as the one shown in Figure 36-5c, are marinecrustaceans that are sessile as adults. Free-swimming barnaclelarvae attach themselves to rocks, piers, boats, sea turtles,whales, and just about any other surface. They then develop ashell composed of calcium carbonate plates that completelyencloses the body in most species. Their swimming appendagesdevelop into six pairs of long legs called cirri (SIR-IE) (singular,cirrus). The cirri extend through openings in the shell, sweepingsmall organisms and food particles from the water and directingthem to the mouth.

Terrestrial CrustaceansSow bugs and pill bugs are terrestrial members of agroup of crustaceans called isopods. Terrestrialisopods lack adaptations for conserving water, suchas a waxy cuticle, and can lose water quickly throughtheir exoskeleton. Therefore, they live only in moistenvironments, such as under leaves and rocks, increvices around garden beds, and in the spacesbetween house foundations and sidewalks. In addi-tion, pill bugs are capable of rolling into a ball whendisturbed or threatened with desiccation, as shown inFigure 36-6. Sow bugs and pill bugs generally feed ondecaying vegetation, but they may also eat gardenbulbs, vegetables, and fruits that lie on or in the soil.

Pill bugs are isopod terrestrialcrustaceans that are often found inmoist environments with decayingvegetation. Pill bugs and sow bugs look similar, but only pill bugs roll upwhen disturbed.

FIGURE 36-6

727

Barnacles on Ships Shipbuilders estimatethat a 12-month growth of barnacles on aship weighing 10,000 metric tons may addanother 30 metric tons to the weight of the ship.

TEACHER RESOURCES

Workbooks

Quick, Data, and Math Labs• Relating Molting to Mortality Rates GENERAL

Teaching TipCrab Sexual Dimorphism Havestudents observe male and femalecrabs of any species. Then askstudents to draw and describeany differences they see. Studentsshould observe that in both malesand females the abdomen is flattened and held beneath thecephalothorax. They should alsonote that the abdomen and telsonare wider and shorter in femalesthan in males. Females may alsobe carrying eggs attached to theabdomen. If fiddler crabs areused, students will notice that inmales one cheliped is muchlarger than the other. Visual

Teaching TipCrayfish Structures Have stu-dents make a Graphic Organizersimilar to the one at the bottomof this page to study the locationsand functions of various crayfishinternal structures. Visual

Using the TableCrayfish Appendages Tell stu-dents that they can use Table 36-1as a starting point for makingtheir flash cards for the ReadingSkill Builder on the previous page.Students will need to include addi-tional structures and details byreading the text. Verbal LS

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TABLE 36-1Crayfish Appendages

Appendage Function

Antennule touch, taste,and balance

Antenna touch and taste

Mandible chewing food

Maxilla manipulating food and drawing water currentsover gills

Maxilliped touch, taste,and manipulating food

Cheliped capturing food and defense

Walking leg locomotion over solid surfaces

Swimmeret creating water currents and transferringsperm (males)

Abdomen

Antennules

MandibleMouth

Maxilla

Maxillipeds

Walking legs

Antenna

Antenna

Telson

Uropod

Cephalothorax(head and thorax)

Cheliped

Swimmerets

(a) (b)

(a) Each of the 20 body segments of acrayfish has a pair of appendages, asseen in this ventral view. (b) Some of the appendages of the anteriorcephalothorax are visible in this closerventral view.

FIGURE 36-7THE CRAYFISH

The crayfish is a freshwater crustacean that is well studied becauseof its size and abundance. Crayfish are structurally similar to lob-sters, which are marine crustaceans. Crayfish, lobsters, crabs, andshrimp are decapods (DEK-uh-PAHDZ), or members of the orderDecapoda. Decapoda means “10 feet,” a name used because thesecrustaceans have five pairs of legs that are used for locomotion.

External StructureThe crayfish’s external structure is shown in Figure 36-7. The bodyis divided into two major sections: the abdomen and the cephalo-thorax (SEF-uh-loh-THAWR-AKS). The cephalothorax consists of twotagmata: the head, which has five segments, and the thorax, whichhas eight segments and lies behind the head. The dorsal exoskeletonover the cephalothorax is a single, tough covering known as thecarapace (KAR-uh-PAYS). The abdomen, the tagma behind thecephalothorax, is divided into six segments.

A pair of appendages is attached to each segment of the crayfish.Several pairs have specialized functions, as summarized in Table36-1. The two pairs of antennae include the branched antennules,which serve as feelers sensitive to touch, taste, and balance. Thelong antennae are also feelers that respond to touch and taste.Crayfish use a pair of mandibles to chew food and use two pairs ofmaxillae (maks-IL-ee) and three pairs of maxillipeds (maks-IL-i-PEDS) tomanipulate food. The posterior pair of maxillae also function in res-piration, and the maxillipeds are sensitive to touch and taste. Themost anterior pair of walking legs, the chelipeds (KEE-luh-PEDS), endin large pincers used for capturing food and for defense. The otherfour pairs of walking legs carry the crayfish over solid surfaces; twoof these pairs end in small pincers that can grasp small objects. Theswimmerets, which are attached to the five anterior abdominal seg-ments, create water currents and function in reproduction.

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Graphic Organizer

Use this Graphic Organizer with Teaching Tip: Crayfish Structures on this page.

Structure Function

Digestive gland Located near the stomach; secretes enzymes for digestion, absorbs nutrients

Gill Extends from base of walking legs; gas exchange

Green gland Located near the antennae; collects and excretes wastes and excess water

Sensory hairs Concentrated on antennae, chelipeds, telson; function in taste, touch

Compound eye Set on moveable stalks at anterior end; detects light, forms images

DemonstrationHorseshoe Crabs Have studentsexamine a preserved horseshoecrab. Point out the two main bodysections—the fused cephalothoraxand the abdomen. The cephalotho-rax has seven pairs of legs, whilethe abdomen has six pairs ofappendages used for swimming.Note that the abdomen is notcurled beneath the body as it isin true crabs. Explain that whereastrue crabs are in the subphylumCrustacea, horseshoe crabs are inthe subphylum Chelicerata, alongwith spiders. Like spiders, horse-shoe crabs lack antennae andhave pincerlike mouthparts.

Visual

Science Literacy Have studentsinvestigate how different varietiesof aquatic arthropods maintainwater balance. Students shouldinclude both euryhaline species,which can tolerate a wide rangeof salinity, and stenohaline species,which have a narrow salinity tolerance. Ask volunteers to give presentations in which theydiscuss the roles of gills, greenglands, and other structures inthis aspect of homeostasis.

Verbal

Crustaceans Have studentsresearch the effects of humans onblue crab populations by usingthe Internet Connect box on this page. IntrapersonalLS

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Green gland

Compound eyeBrain

Stomach

Ventral nerve cord

Heart Ovary

Blood vessel

Intestine

Anus

CarapaceHeart

Intestine

Gills

Ventralnerve cord Walking

leg

Digestivegland

Ovary

Mouth

Esophagus

Ganglia

Digestivegland

(a)

(b)

MB99PE-C38-002-005-A.art

At the posterior end of the crayfish is a paddle-like tail made upof the telson and the uropods (YOOR-oh-PAHDZ), which are attachedto the sixth abdominal segment. Powerful abdominal muscles canpropel the animal rapidly backward in a movement referred to as atail flip.

DigestionThe major parts of the digestive tract of a crayfish are shown inFigure 36-8a. Food passes through the esophagus to the stomach,where teeth made of chitin and calcium carbonate grind the foodinto a fine paste. After the paste is mixed with enzymes secreted bya digestive gland near the stomach, it enters the intestine for fur-ther digestion and absorption. Waste leaves through the anus.

RespirationLike most crustaceans, crayfish have featherlike gills for respira-tion. Figure 36-8b shows that the gills extend from the base of eachwalking leg into a chamber under the carapace. As a crayfish walks,its legs circulate water across its gills. Feathery branches on theposterior pair of maxillae also help direct water over the gills. Eachgill is covered by an extension of the exoskeleton that is thinenough to permit gases to diffuse across the gill surface.

CirculationThe main components of the crayfish’s open circulatory systemare shown in Figures 36-8a and 36-8b. In this system, the dorsalheart pumps a circulatory fluid called hemolymph into severallarge vessels that carry the fluid to different regions of the body.The fluid leaves the vessels and enters spaces within the body,where it bathes the various tissues. It then passes through the gills,where it exchanges carbon dioxide with oxygen in the water. Fromthe gills, the fluid returns to the dorsal part of the crayfish andenters the heart.

The major internal organs of a crayfishare seen in this cutaway side view (a)and cross section through the heartregion (b).

FIGURE 36-8

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Topic: CrustaceansKeyword: HM60368

729 TEACHER RESOURCES

Technology

Transparencies • H28 External Anatomy of

a Crayfish• H29 Internal Anatomy of

a Crayfish

Visual Concepts CD-ROM• Anatomy of a Crayfish

Ghost Crabs When ghost crabs are on thebeach, they carry water with them insidetheir large, sealed gill chambers.

CHEMISTRYCHEMISTRYCONNECTIONCONNECTION

Osmosis and Homeostasis Remind studentsthat osmosis is the diffusion of water acrossa membrane. In brackish or dilute sea water,many crustaceans greatly increase theirurine production to eliminate the waterthat enters their body through osmosis.

Observing Crayfish BehaviorTime Required 15 minutes

Safety Remind students not tomistreat the crayfish. Also, cray-fish can inflict a painful pinch.

Procedural Tips Supply eachgroup with one crayfish in waterand a long rod for tapping.

Answers to Analysis Tapping the ante-rior end causes a tailflip. Tapping theposterior end causes a forward somer-sault. Both allow the animal to escapepredators that are approaching from different directions.

ReteachingCrustacean Quiz Have studentsuse their index cards for theReading Skill Builder to quiz oneanother. Verbal

QuizTrue or False:1.Maxillae are used for

reproduction. (false, maxillae areused for manipulating food and forrespiration)

2. Swimmerets are used for feeding. (false, swimmerets areused for reproduction)

3.Green glands help maintainhomeostasis. (true)

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Answers to Section Review

1. Crustaceans have two pairs of antennae andpaired appendages (some branched). Most havemandibles and a nauplius larva.

2. Copepods are abundant in the plankton and serveas a food source.

3. Mandibles are used for chewing; chelipeds areused for capturing food and defense.

4. Walking and branches of maxillae circulate waterover the gills.

5. Crayfish have open circulatory systems. The heartpumps hemolymph into several large vessels.Hemolymph then enters the spaces within the bodywhere it bathes the tissues. Hemolymph returns to

the gills where it exchanges oxygen and carbondioxide. Then, the hemolymph returns to the heart.

6. The water helps to support their weight. 7. Sample answer: Barnacles develop a hard shell

that encloses and protects their body, and longlegs that sweep food into their mouths.

8. Sample answer: The long antennae may helplocate food that is farther away, and provide more time to sense danger. The short antennulesmay enhance the ability to distinguish betweenfood sources.

9. The crayfish would not be able to excrete wastesand excess water which would build up in the tissues.

730 C H A P T E R 3 6

ExcretionAs freshwater organisms, crayfish live in a hypotonic environment.Remember that a hypotonic environment is one in which the con-centration of solute molecules is lower than that in the organism’scells. Therefore, water constantly enters the tissues of a crayfishby osmosis. This excess water, along with wastes, is eliminated byexcretory organs called green glands, which are visible in Figure36-8a. The dilute fluid collected by the green glands leaves thebody through a pore at the base of the antennae.

Neural ControlThe nervous system of the crayfish is illustrated in Figure 36-8a. Itis typical of arthropods and is similar to the nervous system ofannelids. The crayfish brain consists of a pair of ganglia above theesophagus that receive nerve impulses from the eyes, antennules,and antennae.

Two bundles of nerve fibers extend from the brain and passaround either side of the esophagus to a ganglion that controls themandibles, maxillae, and maxillipeds. The ventral nerve cord runsposteriorly from this ganglion, connecting a series of ganglia thatcontrol the appendages and muscles in the segments of the thoraxand abdomen.

Sensory OrgansCrayfish sense vibrations and chemicals in the water withthousands of small sensory hairs that project from the exoskele-ton. Sensory hairs are visible in Figure 36-1. These sensory hairsare distributed over the entire body, but they are especiallyconcentrated on the antennules, antennae, mouthparts, chelipeds,and telson.

The compound eyes of a crayfish are set on two short, movablestalks. Each eye has thousands of light-sensitive units, each withits own lens. At the base of the antennules are organs that candetect the animal’s orientation with respect to gravity.

1. What characteristics are shared by most or allcrustaceans?

2. What is the important role of copepods inmarine ecosystems?

3. What are the functions of the mandibles and thechelipeds on a crayfish?

4. What structural adaptations of crayfish promoteeffective respiration in water?

5. Describe the type of circulation found in acrayfish.

CRITICAL THINKING

6. Inferring Relationships Why are the largestcrustaceans found only in aquatic environments?

7. Applying Information Barnacles spend most oftheir adult life attached to a marine surface.What structural adaptations for this lifestyle dobarnacles have?

8. Inferring Relationships What is the adaptiveadvantage of having two pairs of antennae?

9. Predicting Results What problem would a cray-fish have if it were born without a green gland?

SECTION 2 REVIEW

Observing CrayfishBehavior

Materials crayfish in containerwith water, tapping instrument

ProcedureCAUTION Crayfish have power-ful pincers that could injure you.Do not place your hand near thecrayfish.1. Gently tap the anterior (head)

end of the crayfish, and recordyour observations.

2. Tap the posterior (tail) end ofthe crayfish, and record yourobservations.

Analysis Describe each behavioralresponse you observed when youtapped the crayfish. How doeseach behavior aid the animal inits survival?

Quick Lab

730TEACHER RESOURCES

Workbooks

Datasheets for In-Text Labs• Observing Crayfish

Behavior GENERAL

OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describesthe structural and functionaladaptations of the cheliceratesand uniramians that allow themto survive on land. Cheliceratesinclude the familiar spiders, anduniramians include centipedesand millipedes.

Ask students to list what comesto mind when they hear the wordspider. If students list words likescary or poisonous, have themclarify what makes spiders scaryor which spiders are poisonous.Discuss with students the accu-racy of the words on their lists.(People may think spiders are scarybecause they believe all spiders bite andare poisonous to humans. Most spiders,in fact, prefer to be undisturbed and runaway if approached.) Verbal

ActivitySpider Anatomy Collect severalspiders and bring them to class.Place them in Petri dishes coveredwith a damp paper towel. Havestudents observe each specimenthrough a dissecting microscope.Help them locate the cephalotho-rax, abdomen, chelicerae, pedi-palps, walking legs, and spinnerets.Ask them to find and count theeyes. (Most spiders have eight simpleeyes.) Point out that spiders haveno antennae. VisualLS

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S U B P H Y L A C H E L I C E R A T A

A N D MY R I A P O DAUnlike crustaceans, nearly all members of the subphyla

Chelicerata, Myriapoda, and Hexapoda are terrestrial.

SUBPHYLUM CHELICERATAThe subphylum Chelicerata, made up of chelicerates, includesspiders, scorpions, mites, sea spiders, and horseshoe crabs.Chelicerates lack antennae and typically have six pairs ofappendages. The first pair of appendages, the chelicerae, are mod-ified into pincers or fangs. The major group in Chelicerata is classArachnida (uh-RAK-ni-duh), which has more than 70,000 species.

Class ArachnidaMembers of the class Arachnida, called arachnids, include spiders,scorpions, mites, and ticks. Like crayfish, arachnids have a bodythat is divided into a cephalothorax and an abdomen. Thecephalothorax usually bears six pairs of jointed appendages: onepair of chelicerae; one pair of pedipalps, which aid in holding foodand chewing; and four pairs of walking legs.

Anatomy of a SpiderSpiders range in length from less than 0.5 mm long to as long as9 cm (3.5 in.) long in some tropical tarantula species. As Figure 36-9shows, the body of a spider is very narrow between thecephalothorax and the abdomen.

SECTION 3

O B J E C T I V E S

● List the characteristics of arachnids,as represented by a spider.

● Explain the adaptations that spidershave for a predatory life on land.

● Identify the unique characteristicsof scorpions, mites, and ticks.

● Compare the characteristics of millipedes and centipedes.

V O C A B U L A R Y

arachnidpedipalpspinneretbook lungtracheaspiracleMalpighian tubule

Walking leg StomachBrain

Heart

Simple eyes

Poison gland

Book lung

CheliceraMouth

GutOvary

Digestive gland

Malpighiantubule

Anus

Spinnerets

Silk glandsGenitalopening

Spiracle

Pedipalp

The major internal organs of a femalespider are shown in this cutaway sideview. The inset shows a closer view of a book lung, one of the spider’sadaptations to life on land.

FIGURE 36-9

731

SECTION 3

Poisonous Spiders Many people believethat all spiders are poisonous and danger-ous to humans. Emphasize that in theUnited States only black widow and brownrecluse spiders have venom that is harm-ful to humans and that these spiders bitepeople only when they are disturbed.

MISCONCEPTIONALERT

TEACHER RESOURCES

Workbooks

Active Reading Guide (Section 3)

Technology

Visual Concepts CD-ROM• Characteristics of Arachnids, Types of Arachnids

Teaching TipOrb Weavers Show a time-lapsevideotape of a spider spinning anorb web. Emphasize that spinningbehavior is instinctive. Explainthat not all spiders make suchgeometrically regular webs; somespiders merely stretch a fewstrands of silk near their nest,while others spin no webs at all.Tell students that chemical com-panies are attempting to developa synthetic spider silk that wouldbe as strong as steel but muchlighter. Fabric woven from thesynthetic silk would then be usedto make products such as para-chutes and bulletproof vests.

Visual

Arachnida Have studentsresearch the hunting and feedinghabits of spiders and other arachnids by using the InternetConnect box on this page.

Intrapersonal

Writing Skills Have studentssearch the library or an on-linedatabase for information aboutspiders around the world. Havestudents make pamphlets describ-ing the spider and its habitat.Encourage them to include pho-tos and diagrams with captionsand labels. Verbal LS

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The chelicerae of spiders are modified as fangs and are used toinject venom into prey. The venom is produced by poison glands inthe cephalothorax and flows through ducts in the chelicerae to thetips of the fangs. Most spiders have eight simple eyes at the ante-rior end of the cephalothorax. Each simple eye has a single lens.

On the tip of the abdomen of many spiders are three pairs oforgans called spinnerets, which are visible in Figure 36-9. Eachspinneret is composed of hundreds of microscopic tubes that con-nect to silk glands in the abdomen. A protein-containing fluid pro-duced in the silk glands hardens into threads as it is secreted fromthe spinnerets. Spiders use their silk threads to spin webs, buildnests, and protect eggs. In some species, spider silk also aids indispersing spiders from one habitat to another. Young spidersmove to new habitats when the wind pulls them through the air bytheir threads.

The nervous, digestive, and circulatory systems of spiders aresimilar to those of crustaceans. Because spiders are terrestrial, how-ever, their respiratory system is quite different. In some spiders, res-piration occurs in book lungs, paired sacs in the abdomen withmany parallel folds that resemble the pages of a book. The folds in abook lung provide a large surface area for gas exchange. Other spi-ders have a system of tubes called tracheae (TRAY-kee-ee) that carryair directly to the tissues from openings in the exoskeleton known asspiracles. Some spiders have both book lungs and tracheae.

The excretory system of spiders is also modified for life on land.The main excretory organs, called Malpighian (mal-PIG-ee-uhn)tubules, are hollow projections of the digestive tract that collectbody fluids and wastes and carry them to the intestine. After mostof the water is reabsorbed, the wastes leave the body in a nearlysolid form with the feces. Thus, the Malpighian tubules help spidersconserve water in terrestrial environments.

Life of a SpiderSpiders feed mainly on insects, although some can catch fish,frogs, and even birds. Different species of spiders are adapted tocapture their prey in different ways. Some chase after prey, somehide beneath trapdoors waiting for prey to approach, and somesnare prey in webs spun from silk. When an insect becomestrapped in the sticky web, the spider emerges from its hidingplace near the edge of the web and paralyzes the insect with itsvenom. Many spiders also immobilize their prey by wrappingthem in silk. They can then consume the body fluids of the preyat a later time.

Spider venom is usually harmless to humans, and most spidersbite only when threatened. There are, however, two kinds of spi-ders in the United States whose bites can be dangerous to humans.They are the black widow and the brown recluse, shown in Figure36-10. The female black widow has a bright red or orange markshaped like an hourglass on the ventral surface of its abdomen.The venom attacks the nervous system.

spiracle

from the Latin spiraculum,meaning “air hole”

Word Roots and Origins

(a)

(b)

The black widow, Latrodectus mactans(a), and the brown recluse, Loxoscelesreclusa (b), are the only two spidersin the United States whose venomis dangerous to humans. Note thered hourglass-shaped spot on theabdomen of the female black widowand the dark violin-shaped marking onthe cephalothorax of the brown recluse.

FIGURE 36-10

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Topic: ArachnidaKeyword: HM60090

732TEACHER RESOURCES

Technology

Transparencies • H30 Anatomy of a Brown

Recluse Spider

Visual Concepts CD-ROM • Spinneret, Feeding Habits

of Spiders

• Hearing Impaired • Learning Disabled • Developmentally Delayed • Attention Deficit DisordersStrategiesStrategiesINCLUSIONINCLUSION

Students who have hearing impairments,learning disabilities, developmental delays,or attention deficit disorders often fail tounderstand complex ideas that they can-not see physically. These students aremore likely to understand if they are givena physical representation that they cansee, hear, or touch. Have students collectorb webs on black construction paper by

bringing the paper in contact with the weband breaking the strands. Students canpreserve the webs by covering them withtape or clear contact paper. Ask studentswhether the webs spun by the same spideron different days appear to be more similarto each other than to webs spun by differentspiders of the same species. Kinesthetic LS

Teaching TipWheeling Spiders To escape fromthe pompilid wasp, the wheel spi-der of the Namib Desert curls itslegs like spokes and rolls rapidlydownhill. The spider’s habitat has steep, sandy slopes that areexcellent for wheeling. Auditory

Group ActivityArthropod Identification Set upobservation stations with pre-served specimens of arachnidsand myriapods. Pair students andask them to classify the specimensinto the following five categories:spider, scorpion, mite or tick, millipede, and centipede. Ask stu-dents to specify the criteria theyused to classify each specimen.(Acceptable criteria should relate tothe number and arrangement of bodysegments, number of legs per segment,and type of head appendages.)

Visual

Teaching TipInsect Control Tell students that people in this country oftenregard centipedes with fear ordisgust. In the tropics, however,many people allow centipedes tolive in their houses to help con-trol insect pests, despite the factthat some centipedes can bite orharm humans. AuditoryLS

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A R T H R O P O D S 733

The brown recluse has a violin-shaped mark on the dorsal sur-face of its cephalothorax. Therefore, it is sometimes called the“violin spider.” The venom of the brown recluse kills and digeststhe tissues surrounding the bite.

A male spider is usually smaller than a female of the same species.When the male is mature, he transfers sperm to special sacs in thetips of his pedipalps. The sperm are then placed in the seminal recep-tacle of the female during mating. As soon as mating has occurred,the male darts away. If he is not quick enough, he may be eaten bythe female. Eggs are fertilized as they pass out of the female into asilken case that she has spun. The female may carry the egg casewith her or attach it to a web or plant. The young spiders hatch inabout two weeks and undergo their first molt before leaving the case.

ScorpionsScorpions, such as the one shown in Figure 36-11, differ from spi-ders in two ways. Scorpions have large, pincerlike pedipalps,which they hold in a forward position. They also have a segmentedabdomen with a large stinger on the last segment, which can becurled over the body. Scorpions usually hide during the day andhunt at night, mostly for insects and spiders. They seize prey withtheir pedipalps and inject venom into the prey with their stinger.Only a few species of scorpions have venom that can be fatal tohumans. Most scorpions live in tropical or semitropical areas, butsome are found in dry temperate or desert regions.

Mites and TicksMites and ticks are the most abundant and most specialized arach-nids. About 30,000 species have been identified, but the actual num-ber of species may be much larger than that. Unlike spiders andscorpions, mites and ticks have a completely fused cephalothoraxand abdomen, with no sign of separation between them.

Most mites are less than a millimeter in length, and some are smallenough to live on particles of dust. They can be found in freshwater,marine, and terrestrial habitats. Many mites are entirely free living,while others are parasites during at least part of their life cycle.Spider mites parasitize fruit trees and many other agricultural cropsby sucking the fluid from their leaves. The larvae of harvest mites—also known as chiggers—attach themselves to the skin of verte-brates, including humans. They break the skin with their cheliceraeand feed on blood, causing swelling and itching. Other species ofmites live on the bodies of chickens, dogs, cattle, humans, and otheranimals, where they feed on sloughing skin, hair, and feathers.

Ticks, such as the one shown in Figure 36-12, are parasites thatfeed on their hosts by piercing the flesh and sucking on the blood.Many species of ticks carry bacteria and other microorganisms intheir guts that may cause diseases in the host. While the tick feeds,the microorganisms are transmitted to the new host. Rocky Mountainspotted fever and Lyme disease are transmitted in this way. Ticksrange in length from a few millimeters to 3 cm (about 1 in.).

The lone star tick, Amblyommaamericanum, is an arachnid thatparasitizes humans and other mammals.

FIGURE 36-12

Scorpions, such as Paruroctonusmesaensis, have pincerlike pedipalpsand a venomous stinger at the end oftheir segmented abdomen.

FIGURE 36-11

733

• Learning Disabled • Developmentally Delayed • Attention Deficit DisordersStrategiesStrategiesINCLUSIONINCLUSION

Students who have learning disabilities,developmental delays, or attention deficitdisorders are more likely to understandcomplex concepts if they are given a physi-cal representation that they can see orfeel. Give students a dozen or more plastic-foam balls of the same size and a box oftoothpicks. Tell students that the balls represent arachnid and myriapod body

segments and that the toothpicks repre-sent appendages. The toothpicks can beused to link the balls together. Have stu-dents use the balls and toothpicks to makea model of each of the following: spider,scorpion, mite or tick, millipede, and centipede. Ask them to identify theappendages on each model. KinestheticLS

DemonstrationMyriapods Bring live millipedesand centipedes to class, and allowstudents to observe them. Askstudents to describe how thesetwo types of myriapods differ intheir locomotion and how thatdifference is related to the feedinghabits of the animals. (Millipedesare slow-moving herbivores; centipedesare fast-moving predators.) Visual

ReteachingTrivia Game Have students writereview questions and answers for a trivia-type game. Pair eachstudent with a partner, and havestudents in each pair take turnsasking their partner the questions.

Interpersonal

QuizTrue or False:1.Chelicerates have six pairs

of appendages. (true)

2.Malpighian tubules function in respiration. (false, malpighiantubules function in excretion)

3.The cephalothorax andabdomen of ticks are fused into one segment. (true)

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Answers to Section Review

1. Arachnids have a cephalothorax and abdomen.The cephalothorax usually has six pairs of jointedappendages: chelicerae, pedipalps, and four pairsof walking legs.

2. Pedipalps aid in holding food and chewing. In spi-ders, they transfer sperm from the male to thefemale’s seminal receptacle.

3. Some spiders spin webs to trap prey. They alsohave chelicerae modified as fangs that injectvenom. Spiders can also immobilize their prey bywrapping them in silk.

4. Scorpions have large pincerlike pedipalps and astinger at the end of their abdomen.

5. Mites are usually less than 1 mm in length, whileticks are a few millimeters to 3 cm in length. Mitescan be free living, but ticks can only be parasites.

6. Millipedes are herbivorous, have rounded bodies,and have two pairs of legs on most segments.Centipedes are carnivorous, have flattened bodies,and have one pair of legs on most segments.

7. Malpighian tubules of spiders remove wastes to theintestine which conserves water, crayfish have greenglands that eliminate wastes and excess water.

8. Sample answer: Spiders feed on harmful insects,which can damage crops or carry diseases.

9. Sample answer: Millipedes aerate soil as theyburrow. They eat decaying matter, which helpsrecycle nutrients.

734 C H A P T E R 3 6

SUBPHYLUM MYRIAPODAThe subphylum Myriapoda (MIR-ee-AHP-uh-duh), includes the classDiplopoda (duh-PLAH-puh-duh), which consists of millipedes, and theclass Chilopoda (KIE-LAHP-uh-duh), which consists of centipedes.Myriapoda means “many feet,” and is so named because myriapodshave many body segments, most of which have one or two pairs oflegs each. Unlike crustaceans, myriapods have one pair ofunbranched antennae. They are terrestrial but lack a waxyexoskeleton. They avoid drying out by living in damp areas.

Class DiplopodaMillipedes are members of the class Diplopoda. Most millipedeshave two pairs of legs on each body segment except the last two.Millipedes may have up to 100 body segments and thus 200 pair oflegs. The legs are well adapted for burrowing through humus andsoil, but because the legs are short, millipedes move slowly. AsFigure 36-13a shows, the bodies of millipedes are rounded.

Millipedes have short antennae and two groups of simple eyeson their head. They have poor vision but a good sense of smell.Millipedes use their maxillae and mandibles to chew on plants ordecaying plant matter in the soil.

Class ChilopodaCentipedes are members of the class Chilopoda. Centipedes mayhave as few as 15 or as many as 175 pairs of legs. In tropical regionscentipedes reach lengths of 30 cm (12 in.). Their bodies are moreflattened than those of millipedes, and their legs are longer relativeto their body, as Figure 36-13b shows. Each body segment behindthe head, except the first segment and the last two segments, hasone pair of jointed legs. The appendages on the first segment aremodified into a pair of poison claws. Long antennae and two clus-ters of simple eyes are located on the head. Centipedes can movequickly in search of earthworms, insects, and other prey. They killthe prey with their poison claws and use their mandibles and max-illae to tear it apart. Most centipedes are not harmful to humans.

1. List the major characteristics of arachnids.

2. Describe the functions of pedipalps.

3. Describe three ways in which spiders areadapted for catching prey.

4. Name two ways in which scorpions differ fromspiders.

5. How do mites and ticks differ?

6. How do millipedes and centipedes differ?

CRITICAL THINKING

7. Making Comparisons Compare the excretorysystem of a spider with that of a crayfish.

8. Inferring Relationships How might spidersbenefit humans?

9. Applying Information A cubic meter of soilmay contain thousands of millipedes. What rolemight millipedes serve in an ecosystem?

SECTION 3 REVIEW

(a) Millipede, Narceus americanus

(b) Giant centipede, Scolopendra sp.

(a) Millipedes have a rounded body andtwo pairs of legs on each body segmentexcept the last two. (b) Centipedes havea flattened body and one pair of legs oneach body segment except the first andthe last two.

FIGURE 36-13

734

AlternativeAssessmentHave students write one to twoparagraphs on crustaceans orarachnids. Ask them to highlightthe organism they think is mostfascinating and explain why.

Study TipHave students create crosswordpuzzles using the vocabularyterms in the chapter. Then, havethem trade puzzles and try tosolve them.

GENERAL

GENERAL

A R T H R O P O D S 735

Phylum ArthropodaSECTION 1

CHAPTER HIGHLIGHTS

Subphyla Chelicerata and MyriapodaSECTION 3

Subphylum CrustaceaSECTION 2

arthropod (p. 723)appendage (p. 723)chitin (p. 723)

compound eye (p. 723)molting (p. 724)

trilobite (p. 724)tagma (p. 724)

mandible (p. 724)chelicera (p. 724)

Vocabulary

nauplius (p. 726)cirrus (p. 727)isopod (p. 727)decapod (p. 728)

cephalothorax (p. 728)thorax (p. 728)carapace (p. 728)abdomen (p. 728)

antenna (p. 728)antennule (p. 728)cheliped (p. 728)swimmeret (p. 729)

telson (p. 729)uropod (p. 729)digestive gland (p. 729)green gland (p. 730)

Vocabulary

arachnid (p. 731)pedipalp (p. 731)

spinneret (p. 732)book lung (p. 732)

trachea (p. 732)spiracle (p. 732)

Malpighian tubule (p. 732)

Vocabulary

● Arthropods are segmented animals that have jointedappendages, an exoskeleton, a high degree ofcephalization, a ventral nerve cord, and an opencirculatory system.

● To grow, an arthropod must shed its exoskeletonperiodically in a process called molting.

● The five major subphyla of Arthropoda are Trilobita,Crustacea, Chelicerata, Myriapoda, and Hexapoda. Thesubphylum Trilobita consists of extinct animals calledtrilobites.

● Crustaceans, members of the subphylum Crustacea, havetwo pairs of antennae. Most crustaceans have a pair ofchewing mouthparts called mandibles and one pair ofbranched appendages on each body segment. The exo-skeletons of many crustaceans contain large amounts ofcalcium carbonate.

● Crustaceans include shrimps, lobsters, crabs, crayfish,barnacles, isopods, copepods, and water fleas. Mostcrustaceans are aquatic, use gills to respire, and have alarval stage called a nauplius.

● The body of a crayfish is divided into a cephalothorax andan abdomen. The appendages on each body segment arespecialized for sensing, feeding, respiration, locomotion,or reproduction.

● Crayfish have a digestive gland that is near the stomachand that secretes enzymes for digestion. Walkingcirculates water across the gills for respiration. Thecirculatory system is open. Green glands assist inexcretion of excess water that enters the body byosmosis.

● Members of the subphylum Chelicerata lack antennaeand have pincerlike mouthparts called chelicerae.

● Arachnids include spiders, scorpions, mites, and ticks.Their bodies are divided into a cephalothorax and anabdomen, and they usually have six pairs of jointedappendages: one pair of chelicerae, one pair of pedipalps,and four pairs of walking legs.

● Spiders have eight simple eyes and chelicerae modified asfangs. Spiders produce silk threads that are used forseveral functions. Spiders are terrestrial; they respire bymeans of book lungs, tracheae, or both. Malpighiantubules function to excrete wastes while conserving water.

● Scorpions have large, pincerlike pedipalps and a stingeron the last segment of the abdomen.

● Mites and ticks have a completely fused cephalothoraxand abdomen. Many species are parasitic, and somespread diseases that affect humans.

● Members of the subphylum Myriapoda have antennae,mandibles, and unbranched appendages.

● Millipedes have rounded bodies and two pairs of jointedlegs on each body segment except the last two segments.Centipedes have flattened bodies and one pair of jointedlegs on each body segment except the first segment andthe last two segments.

735

Answer to Concept Map

The following is one possible answer toChapter Review item 21.

SECTION 0CHAPTER HIGHLIGHTS

moltingmolting

epidermisepidermis

to secrete

enzymesenzymes

starts with a

hormonehormonethat causes the

that digest the old

and replaces the

inner layerinner layer

exoskeletonexoskeleton

TEACHER RESOURCES

Workbooks

• Study Guide• Vocabulary Review• Science Skills• Critical Thinking• Quizzes• Chapter Test• Chapter Test

Technology

Transparencies• Graphic Organizer• Concept Mapping

One-Stop Planner CD-ROM• Concept Mapping

Worksheet GENERAL

GENERAL

GENERAL

GENERAL

GENERAL

GENERAL

ANSWERS

Using Vocabulary1. a. mandible: jawlike mouthpart of

crustaceans; chelicera: pincerlikemouthpart of chelicerates b. isopods:one group of developed antennae;decapods: 2 groups of developedantennae. c. cephalothorax: fusedhead and thorax; abdomen: posteriorto the cephalothorax d. antennae:long feelers that function in touch andtaste; antennules: shorter and aidmaintenance of equilibrium, touch,taste e. cheliped: in crayfish, mostanterior walking legs that have largepincers; telson: located at posteriorend and used for movement f. booklung: in spiders, saclike respiratoryorgan with parallel folds; trachea: inspiders and other arthropods, tube-like respiratory structure that carriesair directly to tissues

2. The cephalothorax has two fused tagmata, the head and thorax.

3. Green glands are excretory structures.The others are for respiration.

4. Tagmata are arranged segments.

Understanding Key Concepts5. Arthropods have segmentation, jointed

appendages, high degree of cephal-ization, and an exoskeleton.

6. Molting begins as the tissues of anarthropod gradually swell; pressurestimulates the release of a hormonethat triggers molting. The epidermalcells respond to this hormone bysecreting enzymes that digest theinner layer of the exoskeleton andbegin replacing it with a new exoskeleton using the digestedmaterials. Eventually the outer layerloosens and breaks away, leaving thenew exoskeleton in its place.

7. Trilobita, Chelicerata, Crustacea,Myriapoda, and Hexapoda

736 C H A P T E R 3 6

CHAPTER REVIEW

USING VOCABULARY1. For each pair of terms, explain how the meanings

of the terms differ.a. mandible and chelicerab. isopod and decapodc. cephalothorax and abdomend. antennae and antennulese. cheliped and telsonf. book lung and trachea

2. Explain the relationship between the cephalotho-rax and the thorax.

3. Choose the term that does not belong in the following group, and explain why it does not belong: book lung, trachea, spiracle, and greengland.

4. Word Roots and Origins The word tagma isderived from the Greek tassein, which means “toarrange.” Using this information, explain why theterm tagma is a good name for the structure thatthe term describes.

UNDERSTANDING KEY CONCEPTS5. Describe the key characteristics of arthropods.

6. Explain how anthropods molt.

7. List the five subphyla of arthropods.

8. Summarize the major characteristics ofcrustaceans.

9. Explain how a barnacle feeds.

10. Summarize the function of the major appendagesof a crayfish.

11. Describe excretion in a crayfish.

12. Compare respiration in crayfish and spiders.

13. Identify the main characteristics of the membersof subphylum Chelicerata.

14. Compare the appendages on the cephalothorax of a spider with those of a scorpion.

15. List three predatory behaviors of spiders.

16. Identify a distinguishing characteristic of mites.

17. Explain how parasitic ticks spread diseases.

18. Identify the main characteristics of the membersof subphylum Myriapoda.

19. Compare the characteristics of millipedes andcentipedes.

20. Summarize how myriapods avoid desiccation interrestrial environments.

21. CONCEPT MAPPING Use the following terms to create a concept map that

sequences the process of molting in an arthro-pod: exoskeleton, enzymes, inner layer, hormone, molting, and epidermis.

CRITICAL THINKING22. Interpreting Graphics Identify structures A

through F in the diagram below.

23. Applying Information Arthropods first lived onland about 400 million years ago. They have sur-vived several time periods in which other phylabecame extinct. What characteristics might haveenabled arthropods to survive and adapt?

24. Relating Concepts A water flea of the genusDaphnia eats algae. How might this organismacquire its food?

25. Inferring Relationships Barnacles are sessile crustaceans. What adaptation enables them tocompete with motile organisms for food? Whatadaptation protects them from predators?

26. Recognizing Relationships The cephalothorax of acrayfish is covered by the carapace, a fused plateof exoskeleton. What are some advantages anddisadvantages of this fused structure?

27. Analyzing Patterns Crayfish have a high concen-tration of sensory hairs on the telson. Whatmight be the advantage of having so many sen-sory structures at the posterior end?

A

B

C

E

F

D

736

CHAPTER REVIEW

8. two pair antennae, mandibles, appendages oneach body segment, and a free-swimming larvacalled a nauplius

9. A barnacle has modified legs called cirri thatsweep water and nutrients into the mouth.

10. antennule: touch, taste, equilibrium; antenna:touch, taste; mandible: chewing; maxilla: manipu-late food, move water over gills; maxilliped: touch,taste, manipulate food; cheliped: capture food,defense; walking leg: locomotion; swimmeret:create water currents, reproduction

11. Wastes and excess water collected by greenglands leave the body via pores at the base of theantennae.

12. Crayfish respire through gills. Spiders respire bymeans of tracheae, book lungs, or both.

13. Chelicerates lack antennae and have chelicerae,which are modified pincers or fangs.

14. Spiders have chelicerae modified into fangs.Scorpions have large pincerlike pedipalps.Scorpions also have a stinger at the end of theirabdomen while most spiders have spinnerets atthe end of their abdomen.

15. Spiders chase their prey, hide beneath trapdoorsand wait for prey, or snare prey in silk webs.

16. Mites have a fused cephalothorax and abdomen.17. Ticks spread disease-causing microorganisms

when they bite their hosts to feed on blood.18. Myriapods are terrestrial, have a single pair of

unbranched antennae, and have many segments.19. Millipedes have round bodies and two pairs of

legs on most segments. Centipedes have flat bodies and one pair of legs on most segments.

ANSWERS

A R T H R O P O D S 737

Standardized Test PreparationDIRECTIONS: Choose the letter of the answer choicethat best answers the question.

1. What do all arthropods have in common? A. spiraclesB. antennaeC. a cephalothoraxD. jointed appendages

2. What is the chitin-containing structure that pro-tects and supports the body of an arthropod?F. a tagmaG. a cheliceraH. an appendageJ. an exoskeleton

3. Which of the following statements about com-pound eyes is true?A. Compound eyes have a single lens.B. Compound eyes are located on the abdomen

of scorpions.C. Compound eyes are found in all arthropods

except crayfish.D. Compound eyes are composed of many indi-

vidual light detectors.

4. What are the major respiratory organs of crayfish?F. gillsG. lungsH. tracheaeJ. book lungs

5. How do mites and ticks differ from spiders?A. Mites and ticks have mandibles. B. Mites and ticks have two pairs of antennae. C. Mites and ticks have a unique respiratory

system.D. Mites and ticks have a fused cephalothorax

and abdomen.

INTERPRETING GRAPHICS: The illustration belowshows four animals. Use the illustration to answer thequestion that follows.

6. Which animal has a chitinous exoskeleton?F. snailG. grasshopperH. hydraJ. squid

DIRECTIONS: Complete the following analogy.

7. mandible : crayfish :: chelicera :A. pill bugB. scorpionC. barnacleD. millipede

INTERPRETING GRAPHICS: The graph below showsdata about molting and two causes of mortality incrabs. Use the graph to answer the questions thatfollow.

8. During which months are you most likely to findcrabs in molt?F. January through MarchG. April through JuneH. July through SeptemberJ. September through January

9. What is the relationship between molting andmortality?A. Molting increases mortality.B. Molting decreases mortality.C. Molting has no effect on mortality.D. Molting and mortality occur at different

times of the year.

SHORT RESPONSESome arthropods are terrestrial and some are aquatic.

Give examples and describe the distinguishing char-acteristics of each type of arthropod.

EXTENDED RESPONSEAll arthropods undergo many cycles of moltingthroughout their lifetime.

Part A Describe the process of molting in arthropods.

Part B Explain how the anatomical structure of anarthropod relates to the function of molting.

For questions involving graphs,be sure to study the graph’s title, axes, and labelscarefully before choosing a final answer.

Jan.

Feb.

Marc

h

April

May

June

July

Aug.

Sept.

Disease

Mol

t an

d m

orta

lity

data

(

in p

erce

ntag

e of

pop

ulat

ion)

Predation In molt

Molting and Mortality Rates

3530252015105

Snail Grasshopper Hydra Squid

737

20. They live in damp areas under rocks and logs.21. The answer to the concept map is found at the

bottom of the Chapter Highlights page.

Critical Thinking22. A: antennule; B: cheliped; C: walking leg:

D: swimmeret; E: uropod; F: telson23. Sample answer: Arthropods are adapted to

diverse environments, which increases the oddsthat they would survive global climate change.The specialized appendages of arthropods proba-bly help them adapt to change also.

24. Sample answer: The eyespot of Daphnia senseswhere light is brightest and thus where mostalgae will be.

SECTION 0Standardized TestPreparation

25. Barnacles have cirri that sweep water and nutri-ents into the mouth. Barnacles have a hard shellthat encloses the body in most species.

26. Sample answer: It strengthens the joint wherehead and thorax meet, but it also eliminatesmovement at this joint.

27. Sensory hairs detect vibrations that may signalthe approach of a predator from the rear, thusproviding a defensive warning system.

Teaching TipTo provide practice under realistic test-ing conditions, give students 20 minutesto answer the Standardized TestPreparation questions.

1. D2. J3. D4. F5. D6. G7. B8. G9. A

Short ResponseSpiders and millipedes are terrestrial.The exoskeleton is lighter, respiration isby book lungs or tracheae, and water is conserved. Crayfish and crabs areaquatic, the exoskeleton is heavier, respiration is by gills, excess water isexcreted by green glands.

Extended ResponsePart A In between molts, the tissues

swell and put pressure on theexoskeleton. Molting is then inducedby hormones. Enzymes digest the old exoskeleton and the epidermissynthesizes a new one. The oldexoskeleton then loosens, breaksalong specific lines, and is shed.

Part B The exoskeleton covers thebody and therefore limits growth.Molting provides a means for allowing growth.

Question 5 Students may have difficultyinterpreting this graph. Remind studentsbefore they try to answer questionsabout a graph to be sure they have readthe title of each axis as well as the key.The line with hollow circles representsthe number of crabs molting at differenttimes of the year. The highest moltingpopulation can be found in betweenApril and June, answer G.

INQUIRY LAB

Time RequiredOne 50-minute class period

Ratings

TEACHER PREPARATION

STUDENT SETUP

CONCEPT LEVEL

CLEANUP

Safety CautionsInstruct students to handle pill bugsand scissors with care, and to washtheir hands with soap after lab.

PreparationEach group will need five live pill bugs,medicine dropper, three sheets of filterpaper, Petri dish, thin slice of potato,4 � 4 in. piece of aluminum foil, lampor flashlight, four 4 � 4 in. pieces offabric having different textures,cellophane tape, scissors.

Materials and EquipmentUse the Lab Materials QuicklistSoftware on the Biology LabGenerator CD-ROM to create a customized list of materials for this lab.

Procedural Tips1. Pill bugs may be found outdoors

under logs and rocks. Keep the pillbugs out of the sun in plastic con-tainers with moist paper towels anda potato slice until lab time.

2. Make a chart on the chalkboard so that results can be combined.Data can be quantified if studentsrecord the position of each pill bugat the end of each experiment.

3. Pill bugs can be released to a natu-ral environment.

E A SY HAR D

Answers to Background

1. Arthropods have jointed appendages and hardexoskeletons made of chitin. Crustaceans have two pairs of appendages on their head that serveas feelers, and a pair of chewing mouthparts calledmandibles. Most breathe with gills.

2. Pill bugs can be found in damp places, such asunder rocks or logs.

3. Most crustaceans are aquatic, but pill bugs are terrestrial.

738 C H A P T E R 3 6

Investigating Pill Bug Behavior

■ Review characteristics of the phylum Arthropoda andthe subphylum Crustacea.

■ Observe the external anatomy of a living terrestrialisopod.

■ Investigate the behavior of terrestrial isopods.

■ safety goggles, lab apron, protective gloves■ 5 live pill bugs for each pair of students■ 1 plastic medicine dropper■ water■ potato■ 3 sheets of filter paper cut to fit a Petri dish■ Petri dish with cover■ aluminum foil■ bright lamp or flashlight■ 4 fabrics of different texture■ cellophane tape■ scissors

Background

1. What are the major characteristics of arthropodsand crustaceans?

2. Where would you expect to find pill bugs?3. How are pill bugs different from most other

crustaceans?

Response to Light

1. Put on safety goggles, lab apron,and protective gloves. Put sev-

eral drops of water on a piece of filter paper untilthe paper becomes slightly moist. Place the filterpaper in the bottom of a Petri dish. Cover half thebottom of the Petri dish with aluminum foil.

2. Check the lighting in the room. The light must below and even during this part of the investigation.

3. CAUTION You will be working with liveanimals. Be sure to treat them gently and

to follow directions carefully. Place five pill bugsin the center of the filter paper. Shine a lampdirectly over the Petri dish so that half the filterpaper is brightly illuminated and the other half is indarkness, shaded by the foil.

4. Based on your knowledge of the natural habitat of pillbugs, can you predict where they will go? Make adata table like the one shown, and record your predic-tion as well as the actual responses of the pill bugs.

Response to Moisture

5. CAUTION Sharp or pointed objects cancause injury. Handle scissors carefully. Cut

a piece of filter paper in half. Moisten one of thehalves with water and place it in the bottom of aPetri dish. Make sure that drops of water do notleak onto the bottom of the dish.

6. Place the dry half of the filter paper in the bottomof the Petri dish, leaving a 2 mm gap between itand the damp filter paper.

7. Place five pill bugs along the boundary between thewet and dry areas. Place the top on the dish.

8. To which side do you predict the pill bugs willmove? Write your prediction in your data table.Observe the pill bugs for 3 to 5 minutes, and recordyour observations in your data table. Do your obser-vations agree with your predictions?

PART B

PART A

SAFETY

MATERIALS

OBJECTIVES

INQUIRY LAB

738

Answers to Parts A–C

4. The pill bugs would be expected tomove into the dark half of the dish.Check that data tables resemble theone shown. Observations recordedby students will vary.

8. The pill bugs would be expected tomove into the wet area of the dish.Observations recorded by studentswill vary.

11. The pill bugs would be expected tocluster around the slice of potato.Observations recorded by studentswill vary.

Answers to Analysis and Conclusions1. The independent variable in Part A

was light. All other conditions shouldhave been the same, so the entire filter paper was moistened.

2. Separating the wet and dry halves ofthe filter paper kept the moisture inhalf the dish.

3. The independent variable in Part Cwas food. If the filter paper were notmoistened, it would have been impos-sible to know whether the pill bugsmoved to the potato slice for moistureor for food.

4. Answers will vary. Pill bugs shouldprefer rough-textured fabrics.

5. Pill bugs seek damp, dark placeswhere they can avoid desiccationand find food.

6. This ability may help pill bugs findsubstrates into which they can dig.

Answers to Further Inquiry1. Sample answer: Students might place

half of a larger dish on ice or shine abright light on half of the dish. If theydo the latter, the entire dish should becovered with aluminum foil so thattemperature is the only variable.Students should predict that the pillbugs will move where the tempera-ture is moderate.

2. Sample answer: Several Petri dishescould be prepared with damp filterpaper covering the bottoms and dif-ferent kinds of food on opposite sidesof each dish. For a more controlledexperiment, slices of potato could besoaked overnight in a strong sugarsolution, salt solution, or water.

A R T H R O P O D S 739

Response to Food

9. Again dampen a piece of filter paper and place it inthe bottom of a Petri dish. Next place a thin slice ofpotato near the edge of the dish.

10. Place five pill bugs in the Petri dish opposite thepotato slice, and place the lid on the dish.

11. Where do you predict the pill bugs will go? Writeyour prediction in your data table. Observe the pillbugs for 3 to 5 minutes, and record your observationsin your data table. Do your observations agree withyour predictions?

Response to Surface Texture

12. Trace the outline of the bottom of a Petri dish on oneof the fabrics. Cut the circle out of the fabric and foldit in half. Then cut along the fold to produce two half-circles.

13. Repeat step 12 using the other three fabrics. Youshould now have eight half-circles.

14. Tape together two half-circles, each of a different fab-ric. Place the full circle in the bottom of a Petri dish,tape side down, as shown in the figure below.

15. On a sheet of paper, draw the fabric circle and labelthe two types of fabric that make up the circle.

16. Place a pill bug in the center of the circle and observeits movements. One student should keep track of theamount of time the animal spends on each fabric.On the drawing that was made in step 15, the otherstudent should draw the path the pill bug travels inthe circle. After 5 minutes, stop your observationsand record the amount of time the pill bug spent oneach fabric.

17. Repeat steps 14–16 for two other pairs of fabrics.18. Return the pill bugs to their container.

Clean up your materials and wash yourhands before leaving the lab.

Analysis and Conclusions

1. In Part A, why was the entire filter papermoistened?

2. In Part B, why was there a slight separation betweenthe wet and dry halves of the filter paper?

3. In Part C, why was the entire filter papermoistened?

4. In Part D, which fabric did the pill bugs prefer?Describe the texture of that fabric.

5. How do the responses of pill bugs to light, moisture,and food in these experiments reflect adaptations totheir natural surroundings?

6. How is being able to detect surface texture a goodadaptation for pill bugs in their natural habitat?

Further Inquiry

1. Design an experiment to investigate the responseof pill bugs to temperature. Think carefully abouthow you will construct your apparatus. Seek approvalfrom your teacher before you actually conduct thisexperiment. How do you think the pill bugs willrespond?

2. Design an experiment to investigate whether pill bugshave preferences for certain types of food.

PART D

PART C

OBSERVATIONS OF PILL-BUG BEHAVIOR

Stimulus Prediction Observation

Light

Moisture

Food

739

TEACHER RESOURCES

Workbooks

Datasheets for In-Text Labs• Investigating Pill Bug Behavior

Skills Practice Labs• Crayfish Dissection

Technology

Biology Lab Video (with Manual)• Observing Pill Bug Behavior