section 1 features of arthropods

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. Section 1 describes thecommon characteristics of arthro-pods. The arthropod family treeshows that this phylum of organ-isms is divided into two groups:those with jaws and those withfangs or pincers.

Tell students that one of thecharacteristics of arthropods is an exoskeleton, or “outer skele-ton,” constructed of the strong,chemically-resistant material calledchitin. Ask students to brainstorma list of advantages and disadvan-tages of an exoskeleton.(Advantages: protection, muscleattachment, and reduction of waterloss. Disadvantages: Does not“stretch” for growth, can be heavy,and can be vulnerable to breaking orcracking.) Visual

DemonstrationBring in the exoskeleton of a lob-ster, crab, tarantula, or otherarthropod. Allow students to exam-ine it with a hand lens and try tofind the areas where muscles wereattached to the interior surface.TAKS 2 Bio 10A; Bio 5A

MotivateMotivate

TAKS 3 Bio 7BLS

Bellringer

FocusFocus

Section 1

664 Chapter 30 • Arthropods

• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Quick Lab GENERAL

GENERAL

GENERAL

Chapter Resource File

English Language Learners

Transparencies

TT BellringerTT Phylogenetic Tree of ArthropodsTT Characteristics of ArthropodsTT Exploration of an Arthropod

• Reading Organizers• Reading Strategies• Occupational Application

Biology Teacher GENERAL

Planner CD-ROM

Section 1 Features of Arthropods

Jointed AppendagesWhether you are looking at a scorpion or a leaf-footed bug, asshown in Figure 1, when you see an arthropod, you will probablynotice its appendages. An is a structure that extendsfrom the arthropod’s body wall. Unlike the parapodia and setae ofannelids, arthropod appendages have joints that bend. The phylumname, Arthropoda, literally means “joint foot.” A variety of jointedappendages are found in arthropods, including legs for walking,antennae for sensing the environment, and mouthparts for sucking,ripping, and chewing food.

Arthropods almost certainly share a distant common ancestorwith the annelid worms. Like annelids, arthropods have a coelomand a segmented body. Arthropod fossils, some as much as 600 million years old, are among the oldest, best-preserved fossilsof multicellular animals. Among the most numerous of the earlyarthropods were the now-extinct trilobites, which lived in the sea. Like modern arthropods, trilobites had segmented bodies and jointed appendages, and they were the first animals to haveeyes capable of forming images. Trilobites became extinct about250 million years ago. The first terrestrial arthropods were probablyscorpions similar to the modern scorpion shown in Figure 1.

appendage

Objectives● Summarize the evolutionary

relationship of arthropodsand annelids.

● Identify the three subphylaof arthropods.

● Describe the characteristicsof arthropods.

● Describe how growthoccurs in arthropods.

Key Terms

appendagethoraxcephalothoraxcompound eyemoltingtracheaspiracleMalpighian tubule

This leaf-footed bug and hairy desert scorpion belong to phylum Arthropoda.

Figure 1 Arthropods

Evolutionary Milestone

Arthropods were the first animals to have jointed appendages. Joints permitpowerful movement, aiding locomotion. Jointed appendages became

specialized in many different ways, helping to create the vast diversityseen among the arthropods.

7 Jointed appendages

ScorpionLeaf-footed bug

7B

8B

8C

5A

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TAKS 2

Student Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TEKS Bio 5A, 7B, 8B, 8C

Teacher Edition TAKS Obj 2 Bio 8C, 10ATAKS Obj 3 Bio 7A, 7B TAKS Obj 5 IPC 4A TEKS Bio 5A, 7A, 7B, 8B, 8C, 10ATEKS IPC 4A

pp. 664–665

Reading Organizer As studentsread this section, have them put thevarious classes of arthropods andtheir descriptions on index cards.The class name should be placed onone side and the description on theother. In addition, students couldmake cards with the class name onone side and examples on the other.Have students use the cards as flashcards to review the section.

Verbal

Interpreting Visuals Explain tostudents that the phylogenetic treein Figure 2 “reads” like a graph upthe Y axis, but not from left toright across the X axis. Explain further: Time progresses up the Y axis. That is, points on the treecloser to the bottom of the pagedenote time longer ago, and pointson the tree closer to the top of thefigure denote more recent time.However, organismal change doesnot progress from left to rightalong the X axis. Organismalchange is shown whether movingto the left or right.

Teaching TipJointed Appendages Havestudents read the EvolutionaryMilestone on page 664. Remindthem that jointed appendages werea major evolutionary development.Have students point out the jointsin the appendages shown inFigure 1. VisualTAKS 3 Bio 7A (grade 11 only); TAKS 3 Bio 7B

LS

GENERAL

TAKS 2 Bio 8C; TAKS 2 Bio 7B

GENERALSKILLBUILDER

READINGREADING

TAKS 2 Bio 8CLS

SKILLBUILDER

READINGREADING

TeachTeach

Chapter 30 • Arthropods 665

did you know?“Jointed Foot” The prefix “arthro” comesfrom a Greek word meaning “joint,” and theprefix “pod” comes from another Greek wordmeaning “foot.” The word arthritis refers to aninflammation of the joints. A podiatrist is adoctor who treats conditions of the feet and apseudopod is also known as a “false foot.”

Arthropod DiversityIf a prize were given for sheer numbers, it would go to the arthro-pods. The total number of arthropod species exceeds that of allother kinds of animals combined. About 900,000 species of arthro-pods have been recorded, and probably at least as many remain tobe classified. There are more species of beetles alone than there areof vertebrates. Scientists estimate that 1018 arthropods are alive atany one moment! The great majority of arthropods are small, about1 mm (0.04 in.) in length. The very smallest are parasitic mites only80 µm (0.003 in.) long. The largest arthropods are gigantic crabs3.6 m (12 ft) across, found in the sea near Japan.

Living arthropods are traditionally divided into two groups,arthropods with jaws and arthropods with fangs or pincers. Asshown in Figure 2, arthropods with jaws belong to either subphy-lum Uniramia (yoo nuh RAY mee uh) or to subphylum Crustacea(kruhs TAY shuh). Arthropods with fangs or pincers belong to sub-phylum Chelicerata (chuh LIS uh rahd uh). Each of these threesubphyla represents a distinct evolutionary line.

This phylogenetic tree shows the relationships among the three arthropod sub-phyla which form two groups: those with jaws and those with fangs or pincers.

Figure 2 Phylogenetic tree

www.scilinks.orgTopic: ArthropodsKeyword: HX4014

Arthropods with jaws

Arthropods with fangsor pincers

Common ancestor

Trilobites(extinct)

SubphylumUniramia

SubphylumCrustacea

SubphylumChelicerata

ClassMalacostraca

ClassArachnida

ClassDiplopoda

ClassChilopoda

ClassInsecta

OrderDecapoda

OrderIsopoda

OrderScorpions

OrderAcari

OrderAraneae

OrderPycnogonida

ClassMerostomata

Millipedes Centipedes Ladybugs Shrimps Pill bugs Scorpions Mites Spiders Sea spiders Horseshoe crabs

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IPC Benchmark Review

To prepare students for the TAKS and accompany the discussion of motion, work and power, have students review Work and Power, TAKS 5 IPC 4A on p. 1056 of the IPC Refresher in the TexasAssessment Appendix of this book.

Interactive Reading AssignChapter 30 of the Holt BiologyGuided Audio CD Program to helpstudents achieve greater success inreading the chapter. Auditory

Teaching TipArthropod Segmentation Havestudents look through this chapterand find examples of trends inarthropod body plans. Ask: Whichare more segmented, larvae oradults? (larvae) Which types ofarthropods show more segmenta-tion? (Answers will vary. Millipedesand centipedes are highly segmented.)

Using the FigureHave students discuss which char-acteristics from the list can be seenin the two arthropods pictured inFigure 3. (Students can see the exter-nal structures on the list, but not theinternal structures.) VisualTAKS 1 Bio/IPC 2D; Bio 3E

LS

TAKS 3 Bio 7B; Bio 5B

GENERAL

LS

GENERALSKILLBUILDER

READINGREADING

Teach, continuedTeach, continued


MISCONCEPTION ALERT

Compound Eyes The individual units in a compound eye do not all see the sameimage. To study the imaging capabilities of ommatidia, the segments that make upcompound eyes, photographers isolatedeyes from insects and shot photos throughthem. These pictures did not show thou-sands of identical images as one mightexpect and as is often portrayed in sciencefiction movies. Instead, the photographersfound the visual effect to be similar to thatof a mosaic. TAKS 1 Bio/IPC 2D; TAKS 2 Bio 10A

Compound Eyes Many arthropods have compound eyes, shown in Figure 4.A is an eye composed of thousands of indi-vidual visual units, each with its own lens and retina. Thebrain receives input from each of the units, and then com-poses an image of an object. While the image formed is notas clear as what you see, arthropods see motion much morequickly. This is why it is so difficult to sneak up on a fly.Some arthropods also have simple, single-lens eyes that donot form images, but simply distinguish light from dark.

Most insects have both compound and simple eyes.In dragonflies and locusts, these simple eyes function ashorizon detectors. The ability to see the horizon helps theinsect stabilize its position during flight.

compound eye

Arthropod Body PlanWhile arthropods may be quite different in appearance, they sharea number of internal and external features, which are summarizedin Figure 3. There is great variation in appearance among arthropodspecies, and not every species has every feature listed. However,these features are characteristic of the phylum as a whole.

Segmentation In arthropods, individual body segments often exist only during thelarval stage. For example, when you look at a butterfly larva (acaterpillar), you can easily see that it has many segments. However,if you look closely at an adult butterfly, you will see only three bodyregions. In most arthropods the many body segments fuse duringdevelopment to form three distinct regions—the head, the (midbody region), and the abdomen. In some arthropods, such asthe crab shown at the top in Figure 3, the head is fused with thethorax to form a body region called the .cephalothorax

thorax

Figure 3 Arthropod characteristics. These eight characteristics are typical ofarthropods, although notall arthropods show eachcharacteristic.

• Jointed appendages

• Segmentation

• Distinct head, often with compound eyes

• Exoskeleton

• Respiration by gills, tracheae, or book lungs

• Open circulatory system

• Excretion through Malpighian tubules

• Wings on many arthropods

Characteristics of Arthropods

Figure 4 Compound eyes.The compound eye of thishouse fly is made of thou-sands of individual units.

Magnification: 22�

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Student Edition TAKS Obj 1 Bio/IPC 2B, 2C, 2D TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7A TAKS Obj 3 Bio 7B TEKS Bio 7A, 7B, 8CTEKS Bio/IPC 2B, 2C, 2D

Teacher Edition TAKS Obj 1 Bio/IPC 2B, 2C, 2D TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 7B TAKS Obj 5 IPC 4A, 4B, 5B TEKS Bio 3E, 5B, 7B, 10ATEKS Bio/IPC 2B, 2C, 2D, 3CTEKS IPC 4A, 4B, 5B

pp. 666–667 IPC Benchmark Mini-Lesson

Biology/IPC Skills TAKS 5 IPC 5B (grade 11 only)Demonstrate wave interactions, including reflectionand refraction.Activity Each lens of a compound eye focuses lightonto its own retina. Focusing light involves bendinglight rays toward a central point. Light waves can bebent when light changes speed by passing through asubstance that is thicker or thinner than air. Have thestudents think of situations in which they have noticedlight bending. (Answers may include looking in a fishtank, using a magnifying glass, or seeing a mirage.)

Teaching TipArmor Relate the weight of anexoskeleton to that of the bodyarmor worn by the knights of theMiddle Ages. The knights had to beassisted onto their horses, and theweight of the armor was very tir-ing. Even today, law enforcementofficers sometimes dislike wearingbulletproof vests because they aretoo heavy and hot to wear.TAKS 1 Bio/IPC 2C

GENERAL


Evaluating JointedAppendages

Skills AcquiredMeasuring, predicting,drawing conclusions

Teacher’s Notes Bring in a crab exoskeleton to demonstrate the range ofmotion in one jointed appendage.

Answers to Analysis1. A person’s arms would be use-

less for bringing food to one’sown mouth.

2. An animal with jointedappendages would have amuch greater range of motion,which would be better formanipulating food.

3. Answers will vary. One advan-tage is that the animal couldmove its sense organs by mov-ing particular appendagesinstead of its whole body.

CulturalAwarenessCulturalAwareness

Crickets To the Japanese, crickets are considered pets and a delightful source ofmusical and artistic pleasure. Favorite petcrickets are often given elaborate cages andbeautiful porcelain water dishes. Japanesecricket owners even “tickle” their cricketswith delicate hand-carved brushes to encour-age them to sing. To the British, a cricket onthe hearth is a sign of good luck. Bio/IPC 3C

Exoskeleton The outer layer of the arthropod body is a rigid exoskele-ton (often called a shell) composed primarily of chitin.The exoskeleton is thin and flexible where the joints of theappendages are located. Muscles attached to the interiorsurfaces of the exoskeleton can pull against it, causing theanimal’s joints to bend. As shown in Figure 5, manyarthropods can use their jointed appendages to performcomplex movements. While chitin is tough, it is brittle andbreaks easily. As arthropods increase in size, theirexoskeletons must become thicker to withstand the pull oflarger muscles without breaking. However, an increase inthickness of the exoskeleton adds weight, restricting the size arthro-pods can reach.

The exoskeleton of the different arthropod groups varies greatlyin thickness. If you have ever attempted to swat a large insect, youknow that its exoskeleton can be difficult to crush. Crustaceans, forexample, have a thick, relatively inflexible exoskeleton. In compari-son, the exoskeleton of other insects and some arachnids is fairlysoft and flexible. Regardless of the nature of an arthropod’sexoskeleton, it provides protection from injury and helps to preventwater loss.

Figure 5 Jointedappendages. The joints in the legs of this praying mantispermit it to perform manycomplex movements, such as manipulating prey.

Evaluating JointedAppendagesTo understand the importance of jointed appendages,test your range of movement without and with bendingyour joints.

Materials

meterstick, paper, and pencil

Procedure

1. Work in pairs, and assign oneperson to be the test subjectand one person to record thedata.

2. The test subject extends onearm straight out in front ofthe body. The subject thenplaces a meterstick along theinside of the arm, as shownin the illustration. The elbowshould not be bent.

3. The recorder measures andrecords the distance alongthe meterstick that the testsubject can reach withextended (not bent) fingers.

4. The test subject now tries toincrease the range of move-ment by bending the fingersonly. The recorder measuresand records the closest andfarthest distance along themeterstick that can bereached.

5. The test subject now tries toincrease the range of motionby bending the elbow. Therecorder measures andrecords the closest and far-thest distance along themeterstick that can bereached.

Analysis

1. Describe how eating break-fast might be different if youdid not have joints on yourfingers and at your elbows.

2. Predict the advantages ananimal with jointedappendages has over an ani-mal without jointedappendages when capturingand consuming food.

3. Predict the advantages foran arthropod that has senseorgans (eyes and odor detec-tors) on the ends of jointedappendages.

2B 2C 2D

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TAKS 1 Bio/IPC 2B, 2C, 2D

TAKS 1

IPC Benchmark Fact

In order to distinguish mass and weight, point out tostudents that when the thickness of an exoskeletonincreases, more mass (i.e., matter) is added. Theincreased mass then results in a proportional increasein the pull of gravity on the arthropod which therebyincreases its weight, which is a measure of the forceof gravity. Finally, ask students how an exoskeletonlimits the size and movement of arthropods.TAKS 5 IPC 4A, 4B

Teaching TipMolting Ask students to brain-storm some of the problems inherentin molting. (Emerging from anexoskeleton can be hazardous to anarthropod. For about two hours after emerging from an outgrownexoskeleton, an arthropod is vulnera-ble to predators and the environmentbecause its new exoskeleton has notyet hardened.) Ask students howarthropods can protect themselvesduring molting. (Arthropods usuallyhide until their new exoskeletonshave hardened.)

Teaching TipArthropod Respiratory OrgansInsects have hollow branching tubescalled tracheae that carry air into thebody’s tissues. Spiders have leaflikeplates called book lungs that have alarge surface area to exchange oxy-gen and carbon dioxide. Lobstershave gills that also have a large sur-face area for gas exchange.TAKS 2 Bio 10A

GENERAL

TAKS 3 Bio 7B



Answer

Topical products for head licecontain the insecticide permethrin.Most products are shampoos orcreams used to treat the scalp.After such treatments, health carepractitioners suggest combing thehair with a fine-toothed comb toremove the eggs. Creams are alsoavailable to treat the skin all overthe body. The spread of lice canusually be prevented if peopleavoid sharing combs, brushes,hats, towels, and other items thatmay transfer lice or eggs from oneperson to another.

Bio 3B

Real Life

MISCONCEPTION ALERT

Albino Roaches? People often see whatthey think are “albino” insects, such asroaches. These white insects are not reallyalbinos. They have just shed their exoskele-tons recently and full coloration has not yet returned.

Muscle cell

Trachea

Spiracle

Molting A tough exoskeleton protects an arthropod from predators andhelps prevent water loss. But an exoskeleton cannot grow larger, soan arthropod cannot simply grow bigger, as many other animals do.Imagine blowing up a balloon inside a soft drink can—after a cer-tain point, the balloon cannot get any bigger. Arthropods have thesame problem. In a process called , or ecdysis (EHK duhsihs), they shed and discard their exoskeletons periodically. Moltingis triggered by the release of certain hormones. Just before molting,a new exoskeleton forms beneath the old one. When the newexoskeleton is fully formed, the old one breaks open. The arthropodemerges in its new, still-soft exoskeleton, as shown in Figure 6.The new exoskeleton hardens within a few hours or a few days,depending on the species.

Respiration The majority of terrestrial arthropods respire through a network offine tubes called (TRAY kee ee), as shown in Figure 7. Airenters the arthropod’s body through structures called andpasses into the tracheae, delivering oxygen throughout the body.Valves that control the flow of air through the spiracles and preventwater loss were a key adaptation for the first arthropods thatinvaded land more than 400 million years ago.

spiraclestracheae

molting

A complex series of hollow tubes called tracheae run through the bodies of most terrestrial arthropods.

Figure 7 Tracheal system of a beetle

Figure 6 Molting. Thisgreen cicada is emerging fromits old exoskeleton, which itleaves behind as a colorlessghost of itself.

Real LifeHead lice often infectentire schools.Head lice are notoriouslydifficult to control. Havingclean hair will not preventa head lice infection, andanti-lice shampoos oftenfail to kill immature head lice.

Finding InformationResearch the latest reme-dies for treating head lice,and find out how to avoidinfection. 3B

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Student Edition TAKS Obj 2 Bio 8C TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 7B TEKS Bio 3B, 5A, 7B, 8B, 8C, 10A

Teacher Edition TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B TEKS Bio 3B, 5A, 7B, 8B, 8C, 10A

pp. 668–669

Answers to Section review

1. Annelids and arthropods almost certainly sharea common ancestor.

2. Jointed legs, an exoskeleton, and segmentation.

3. Compound eyes receive images from each lensand send them to the brain, where one image isformed.

4. Arthropods cannot grow without shedding theirexoskeleton. A new exoskeleton forms, and theold one splits and is molted. The new exoskele-ton hardens, and the cycle begins again. Bio 5A

TAKS 2 Bio 10A

TAKS 2 Bio 8C

TAKS 3 Bio 7B5. Concept maps will vary but should include the

subphyla Uniramia, Crustacea, and Chelicerata,and two examples in each subphylum.

6. A. Incorrect. Malphighiantubules function in excretion. B. Incorrect. Inan open circulatory system, the blood movestoo sluggishly to efficiently deliver oxygen totissues. C. Incorrect. The exoskeleton coversthe body, protecting the arthropod. D. Correct.The tracheae are a network of fine tubes thatdeliver oxygen throughout the arthropodbody. TAKS 2 Bio 10A

Bio 8B


An Arthropod on the MoveTeaching StrategiesAsk students if they have seenmigrating monarch butterflies.The largest numbers of mon-archs can be observed duringthe second and third weeks ofOctober in west central Texas.Good places to observe includeSeminole Caynon State HistoricPark and most locations alongthe Devil’s River and Frio River.

Discussion• For monarchs born in the fall,

what are the advantages ofwaiting until the followingspring to breed? (Larvae bornin the spring will be more likelyto survive due to warmer cli-mate and greater availability offood/vegetation.)

ReteachingHave students write the character-istics of arthopods on index cardsand quiz one another with them.

Interpersonal

QuizTrue or False:

1. One characteristic of arthropodsis a closed circulatory system.(False. Arthropods have open cir-culatory systems.)

2. When an arthropod molts, itsheds its exoskeleton. (True)

AlternativeAssessmentHave students write review ques-tions and answers for a trivia-typegame. Pair each student with apartner, and have the students ineach pair take turns asking theirpartner the questions.

InterpersonalLS

GENERAL

TAKS 2 Bio 8C

TAKS 2 Bio 8C

GENERAL

TAKS 2 Bio 8CLS

CloseClose

Section 1 Review

State the evolutionary relationship of the arthro-pods and the annelids. 7B

Describe the three externally visible character-istics common to all arthropods. 8C

Summarize how compound eyes function.

Describe how arthropods grow. 5A

Critical Thinking Relating Concepts Drawa concept map of the three subphyla of arthropods,with two examples of each subphylum. 8B

Oxygen is delivered through-out an arthropod’s body by the A Malpighian tubules. C exoskeleton.B blood. D tracheae.

TAKS Test PrepTAKS Test Prep

An Arthropod on the Move

The monarch butterfly, Danausplexippus, is a long-distance

traveler. Each year, millions ofthese insects migrate from sitesacross the United States andCanada to their wintering groundsin central Mexico. Some monarchsfly up to 4,000 km on their journey.

Generations of MigrantsFour to five generations of mon-archs are born each year. Inspring, most monarchs are foundin the southern United States.The offspring of each successivegeneration move farther north tobreed. Monarchs born in early fallpostpone breeding until the nextyear. They respond to the shorter

days and lower temperatures bybeginning their long migration toMexico, where they remain untilthe following March.

Monarchs funnel through Texasduring both the spring and the fall migrations. In the fall, theyuse two main flyways. One, whichpasses through the center of thestate, is about 300 km wide and isused by most monarchs. Theother flyway follows the coastline.

Finding Their WayScientists at the University ofTexas at El Paso have shownthat monarchs use at least twomethods to chart their course.Under clear skies, the butterflies

note the direction of the sun withrespect to north. On cloudydays, they find their way bydetecting Earth’s magnetic field.The researchers demonstratedthe latter method by collectingmonarchs in the fall and placingthem in a chamber where themagnetic field could be blockedor reversed. In the absence of amagnetic field, the butterflies flewin random directions. When themagnetic field was reversed, theyflew to the northeast, the oppositeof their normal migratory direction.

Excretion Terrestrial arthropods have a unique excretory system that efficientlyconserves water and eliminates metabolic wastes. This system is com-posed of excretory units called Malpighian (mal PIHG ee uhn)tubules. are slender, fingerlike extensions fromthe arthropod’s gut that are bathed by blood. Water and smalldissolved particles in the blood move through the tubules and into thearthropod’s gut. As this fluid moves through the gut, most of thewater, valuable ions, and metabolites from the fluid are reabsorbedinto the arthropod’s body tissues by osmosis. Metabolic wastesremain in the gut and eventually leave the body through the anus. Youcan see the Malpighian tubules on the grasshopper in Up Close:Grasshopper, in Section 2 of this chapter.

Malpighian tubules

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TAKS 3

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. Section 2 describes thecharacteristics of arachnids: spiders,scorpions, ticks, mites, and daddylonglegs.

Ask students to list what comes tomind when they hear the word“spider.” For homework, havestudents determine whether theirpreconceptions are accurate. Forexample, if students list “poison-ous” have them research whichspiders are poisonous. Are therepoisonous spiders in your state? Ifstudents list words like “scary,”have them clarify what characteris-tics of spiders make them scary andhave them determine the accuracyof these characteristics.

ActivityPoisonous Spiders Have studentssearch the library or an on-line data-base for information about poison-ous spiders around the world, suchas the Australian funnel-web spider,whose bite can be lethal if leftuntreated. Have students make apamphlet describing the spider andits habitat, the symptoms caused bythe spider’s bite, and the measuresa person should take if bitten. Verbal TAKS 1 Bio/IPC 2C, 2D

LS

MotivateMotivate

TAKS 1 Bio/IPC 2C, 2D

Bellringer

FocusFocus

Section 2


• Lesson Plan• Directed Reading• Active Reading GENERAL

GENERAL


• Reading Organizers• Reading Strategies

Planner CD-ROM

Transparencies

TT BellringerTT Anatomy of a Spider

Section 2 Spiders and OtherArachnids

Arachnid ModificationsPerhaps no other group of animals is more disliked and feared byhumans than the arachnids—spiders, scorpions, ticks, mites, anddaddy longlegs. While it is true that some spiders and scorpions arehighly venomous, in general these creatures do more good thanharm. For example, many spiders are major predators of insect pests,and gardeners usually welcome them. Arachnids (uh RAK nihdz)form the largest class in subphylum Chelicerata. Two minor classes,marine horseshoe crabs and sea spiders, also belong to this subphy-lum. The members of subphylum Chelicerata have mouthparts called

(kuh LIS uh ree) that are modified into pincers or fangs,as shown in Figure 8.

The arachnid body is made up of a cephalothorax and anabdomen. There are no antennae, and the first pair of appendagesare chelicerae. The second pair of appendages are , whichare modified to catch and handle prey. (The pedipalps are sometimesspecialized for sensory or even reproductive functions.) Followingthe pedipalps are four pairs of appendages called walking legs.

All arachnids except some mites are carnivores, and most are ter-restrial. Since arachnids do not have jaws, they are able to consumeonly liquid food. To do so, the arachnid first injects its prey withpowerful enzymes that cause the prey’s tissues to liquefy. Then thearachnid sucks the liquid food into its stomach.

SpidersThe chelicerae of spiders are modified into fangs.Poison glands located in the spider’s anterior endsecrete a toxin through these fangs. The toxin kills orparalyzes the prey. The spider then injects enzymesinto the prey that digest its tissues, and the spidersucks up the liquid food. Spiders are importantpredators of insects in almost every terrestrialecosystem. Only two species of spiders living in theUnited States, the black widow and brown recluse,are dangerous to humans. Not all spiders build

beautiful webs as the orb-builders do. Most spiders can secretesticky strands of silk from appendages called located atthe end of the abdomen. Tubes located on some spinnerets do notproduce silk. Instead, they excrete a sticky substance that the spidercan use to make some silk strands adhesive.

spinnerets

pedipalps

chelicerae

Objectives● Summarize the characteris-

tics of arachnids.

● Identify the internal andexternal characteristics ofbrown recluse spiders.

● Compare spiders, ticks, andmites.

● Identify the health threatsposed by some arachnids.

Key Terms

chelicerapedipalpspinneret

Figure 8 Chelicerae. Thebaboon spider’s pointed blackchelicerae (fangs) and its twopair of pedipalps are clearlyseen in this close-up of itshead region.

8C

8C

8C

4D 11D

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Student Edition TAKS Obj 2 Bio 8C TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 4DTAKS Obj 3 Bio 7B TEKS Bio 4D, 7B, 8C, 10A, 11D

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2DTAKS Obj 2 Bio 8C, 10ATAKS Obj 3 Bio 4D, 7BTEKS Bio 4D, 7B, 8C, 10A, 11DTEKS Bio/IPC 2C, 2D

pp. 670–671


did you know?Spider Silk All spiders have silk glands andorgans called spinnerets that spin the silk. Somespiders spin webs that are used to catch prey.Others may use webs to protect their eggs andyoung. Spiders do not discard their old webs buteat them to recycle the protein in them. Spidersalso use silk to wrap up prey, or they spin stickyballs to throw at prey. Burrow-dwellers linetheir underground homes with silk. Bio 12C

Brown Recluse Spider

Teaching Strategies Havestudents look up the wordrecluse in a dictionary. (Arecluse is one who lives in seclu-sion or isolation.) Explain thatduring the day, brown recluseshide in corners or other darkareas, such as old boxes thatare seldom opened. They areactive at night. Caution stu-dents that if they live in an areawhere brown recluses live, theyshould wear gloves when theyclean out an area that has beenleft undisturbed for some time.

Explain that many spiders spinat least two varieties of silkthreads. Dry threads are usedto form the web’s radial frame-work; sticky threads arearranged in a spiral around theradial threads. Ask studentswhat advantage a spider gainsby spinning both dry andsticky threads. (Spiders avoidbecoming trapped in their ownwebs by walking on the dryradial threads.)Discussion• Ask students what the

adaptive advantage of venomproduction might be in bees,ants, scorpions, spiders, andcentipedes. (Bees and ants usevenom for defense. Scorpions,spiders, and centipedes usevenom to capture prey.)

• Look at the art showing theinterior of the spider. Whatstructures are present thatare characteristic of arthro-pods in general? (jointedappendages, open circulatorysystem, Malpighian tubules,book lungs)

• What characteristics ofarachnids are present?(pedipalps, chelicerae)

TAKS 2 Bio 8C, 10A; TAKS 3 Bio 7B

Up Close

Up CloseBrown Recluse Spider(Violin Spider)

Scientific name: Loxosceles reclusa

Size: Length of females, up to 10 mm (0.5 in.); males are smaller

Range: South-central United States, from central Texas toAlabama, north to southern Ohio

Habitat: Dark, dry sheltered sites outdoors or indoors

Diet: Small insects

●

●

●

●

●

Characteristics

Respiration Book lungs contain stacks

of thin blood-filled plates of tissue. Air enters

the book lungs through slits on the under-

side of the spider’s abdomen and passes

over them. Blood flowing through the plates

picks up oxygen by diffusion.

Cephalothorax Six eyes, in pairs, form a

semicircle around the front of the cephalo-

thorax. Two chelicerae and two pedipalps are

located next to the mouth. Four pairs of walk-

ing legs attach to the cephalothorax, which is

marked on top with a distinctive violin shape.

Abdomen The abdomen

contains most of the spider’s

organs. Spinnerets located

here are used to spin small,

irregular webs.

Walking leg Gut

Malpighiantubule

Digestive gland

Heart

Brain

Simple eyes

Mouth

Air flow

Chelicera

Stomach

Pedipalp

Silk glandsGenitalopening Spinnerets

Anus

▲ Ovary

▼ Poison gland

▼ Book lung

Poison gland Poison

glands are connected to the

fanged chelicera. The venom

of the brown recluse is

harmful to many humans.

The severity of a person’s

reaction depends on the

individual’s sensitivity and

how much venom is injected.

Reproduction During mating,

the male uses its pedipalps

modified into sperm storage

organs to insert sperm into the

female’s body. The female lays

an average of 20–50 eggs inside

a silk cocoon that she spins and

hangs in her web.

671

TAKS 2TAKS 3

Vocabulary Arachnids are namedfor Arachne, a weaver in Greekmythology. Arachne boastfullychallenged the goddess Athena to aweaving contest. Arachne produceda beautiful tapestry. Athena was soenraged by Arachne’s skill that shechanged Arachne into a spider.

Verbal

ReteachingHave students create crosswordpuzzles using the vocabulary termsin this section. Then have themtrade puzzles and try to solve them.

Verbal

Quiz1. Define the term “chelicerae.”

(Chelicerae are arachnid mouth-parts that are modified into fangsor pincers.)

2. Explain the meaning of the fol-lowing statement: All arachnidsexcept some mites are carni-vores. (The statement means thatmost arachnids feed on animals,not on plants.)

AlternativeAssessmentHave students write an essay onarachnids, highlighting the organismthey think is the most fascinatingand explaining why. VerbalTAKS 1 Bio/IPC 2C, 2D

LS


Bio 5A

GENERAL

TAKS 1 Bio/IPC 2DLS

CloseClose

LS

GENERALBUILDERSKILL


Answers to Section Review

1. Spider—fangs modified from chelicerae; pedi-palps; two segments (cephalothorax andabdomen). Scorpion—stinger; pedipalps modi-fied into pincers; long, slender, segmented body.Mite—chelicerae and pedipalps; head, thorax,and abdomen fused into one

2. They are up to 10 mm in length, dark brown,with a violin shape on their cephalothorax.

3. Only two spiders in the United States are poi-sonous to humans. In contrast, many tickstransmit diseases, such as Lyme disease andRocky Mountain spotted fever.TAKS 3 Bio 4D; Bio 11D

TAKS 2 Bio 8C

TAKS 2 Bio 8C

4. The identification is not correct. Scorpionshave no antennae.

5. A. Incorrect. Homeostasis is themaintenance of stable internal conditions inspite of changes in the external environment.B. Correct. Parasitism is a relationship inwhich one organism feeds on another. C. Incorrect. Commensalism is a relationship in which one organism benefits and the other is neither harmed nor helped. D. Incorrect.Mutualism is a relationship in which bothorganisms benefit. TAKS 3 Bio 12B

TAKS 2 Bio 8C


www.scilinks.orgTopic: Mites and DiseaseKeyword: HX4123

Compare the body plan of spiders, scorpions,and mites, including differences in appendages.

Describe the body and coloring of a brownrecluse spider. 8C

Critical Thinking Summarizing InformationExplain why a tick bite is more a cause for concernthan the bite of most spiders. 4D 11D

Critical Thinking Evaluating ConclusionsIs an animal that has grasping pincers, a seg-mented body, and two antennae correctly identifiedas a scorpion? Why or why not? 8C

The relationship between atick and a dog is an example of 12B

A homeostasis. C commensalism. B parasitism. D mutualism.


Section 2 Review

Scorpions and MitesTwo other familiar groups of arachnids are scorpions and mites.Like spiders, they have chelicerae and pedipalps, but these struc-tures are modified differently.

ScorpionsScorpions have long, slender, segmented abdomens that end in avenomous stinger used to stun their prey. The stinger-tippedabdomen is usually folded forward over the rest of the scorpion’sbody, a trait that makes scorpions instantly recognizable. The pedi-palps of scorpions are large, grasping pincers, which are used notfor defense but for seizing food and during sexual reproduction.

MitesMites are by far the largest group of arachnids. Some mites, includ-ing chiggers and ticks, are well known to humans because of their irri-tating bites. They are easily recognizable because their head, thorax,and abdomen are fused into a single, unsegmented body. Most adultmites, such as the one shown in Figure 9, are quite small, typically lessthan 1 mm (0.04 in.) long, but ticks grow larger. Many aquatic mitesare herbivores, while terrestrial mites are usually predators.

Most mites are not harmful, but some are plant and animal pests.While feeding, plant mites may pass viral and fungal infections tothe plant. Blood-sucking ticks attach themselves to a host, often ahuman. Lyme disease is spread by bites from infected deer ticks,like the one shown in Figure 9.

Figure 9 Mites. The housedust mite is a major cause ofallergies in humans. The biteof an infected deer tick cancause Lyme disease. Dust mite Deer tick

8C

672

Student Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 4D TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 12B TEKS Bio 4D, 7B, 8B, 8C, 11D, 12B

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 4D, 12B TEKS Bio 4D, 5A, 8C, 11D, 12BTEKS Bio/IPC 2C, 2D

pp. 672–673

Section 3

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. Section 3 describes thegeneral body plan and life cycles ofinsects. Then, after discussinginsect flight and the social insects,Section 3 includes the centipedesand millipedes, members (with theinsects) of the Subphylum Uniramia.

Prepare a handout for studentswith the following facts: There aremore arthropod species than allother animal species combined.Eighty-five percent of all animalsare arthropods. Arthropods are ourmain competitors for food. If leftunchecked (by nature), they couldtake over the world. There are 200million insects for every human onEarth. Insects destroy 10–15 per-cent of the world’s food supplyeach year. Insects have been onEarth for approximately 300 mil-lion years. Bush crickets have earson their knees. Have the studentsread the facts while you take atten-dance, then ask students which factwas the most interesting to themand why.

IdentifyingPreconceptionsPeople use the terms “insects” and“bugs” freely to refer to manyorganisms, some of which are notinsects. Ask students to list 5organisms that they think areinsects. Then have students com-pare the characteristics of theorganisms they listed with those ofinsects. Have students determinewhether or not the organisms ontheir lists are truly insects.TAKS 1 Bio/IPC 2C, 2D; TAKS 2 Bio 8C

GENERAL

MotivateMotivate


Bellringer

TAKS 2 Bio 8C

FocusFocus


Transparencies

TT BellringerTT Four Orders of InsectsTT Insect MouthpartsTT Complete and Incomplete

MetamorphosisTT Anatomy of a Grasshopper

• Reading Organizers• Reading Strategies• Supplemental Reading

Journey to the Ants

Planner CD-ROM

• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Data Lab GENERAL

GENERAL

GENERAL


Insect DiversityAnyone who has ever been on a picnic in a wooded area does nothave to be told that insects are numerous. Ants, mosquitoes, gnats,flies, bees, crickets—they all want to join in while the cicadas sing inthe background. These animals all belong to the arthropod subphy-lum Uniramia, an enormous group of mostly terrestrial arthropodsthat have chewing mouthparts called (jaws). Uniramiansconsist of three classes: Insecta (insects), Diplopoda (millipedes),and Chilopoda (centipedes).

The insects are by far the largest group of organisms on Earth,with more than 700,000 named species. Most scientists agree that there may be several million insect species in existence, withmost of the undiscovered species living in the tropics. As shownin Figure 10, more than 50 percent of all named animal speciesare insects. More than 90 percent of these species belong to one of the four orders shown in Table 1. To read about other ordersof insects, see “A Six-Kingdom System of Classification” in theAppendix of this book.

mandibles

Insects and Their Relatives

Section 3

Key Terms

mandiblemetamorphosischrysalispupanymphcaste

The predominance of insects, especially beetles (Coleoptera), in the living worldis illustrated by the blue section of this pie chart.

Figure 10 Species of insects

Hym

enop

tera

Lepidoptera

Oth

er in

s ec t

s

All other species

Diptera

Millipedes,centipedes

Spiders

Mollusks

Protists

Vertebrates

Fung

i

Coleoptera Floweringplants

Table 1 Four Orders of Insects

Coleoptera Beetles, 350,000

“shield winged” weevils

Diptera Flies, 120,000

“two winged” mosquitoes

Lepidoptera Butterflies, 120,000

“scale winged” moths

Hymenoptera Ants, “membrane wasps, 100,000winged” bees

Order Examples Number of species

8C

8B

Objectives● Describe the characteris-

tics of insects.

● Compare complete and in-complete metamorphosis.

● Identify the external and in-ternal structures of the EasternLubber grasshopper.

● Compare millipedes andcentipedes with insects.

673

TAKS 2

DemonstrationBring examples of live or preservedinsects to class for display, or bringdetailed photographs of insectsfrom a nature magazine. Allow stu-dents to compare the animals. Askthem to point out examples of thearthropod characteristics. (jointedappendages, segmentation, exoskele-ton, wings, spiracles, etc.) Visual

Using the FigureUse Figure 12 to point out how themouthparts of different insects areadapted for different functions.Grasshoppers cut and chew theirfood, mosquitoes puncture skin todraw out blood, and flies soak upfluids with their mouthparts.

Visual

Teaching TipJumping Fleas Dr. MiriamRothschild is a world-class ento-mologist and the world’s expert onfleas. In 1977 she published apaper giving the first description ofthe flea’s jumping mechanism.Using high-speed photography thatrecords 10,000 frames per second,Dr. Rothschild concluded that aflea’s ability to leap is equivalent toa human jumping over a tower30,000 times before exhaustion setsin. She also found that a jumpingrabbit flea has 230 times moreacceleration than a spacecraft reen-tering the Earth’s atmosphere aftera trip to the moon.TAKS 5 IPC 4A; Bio 3F

TAKS 3 Bio 7B; Bio 8BTAKS 2 Bio 6D (grade 11 only);LS

TAKS 1 Bio/IPC 2C, 2D; TAKS 2 Bio 8CLS

TeachTeach

and location of death and may help provideinformation in investigations of sudden death,traffic accidents with no obvious cause, andpossible criminal misuse of insects. Mostforensic entomologists hold the Ph.D. degree.However, a student with a BS degree and amajor in entomology would be qualified for aposition as a research assistant, technician, orstaff member in a research laboratory. Bio 3D


CareerCareerForensic Entomologist Maggots crawlingout of eye sockets are usually the stuff of hor-ror films. But to forensic entomologists,insects and cadavers are part of their work.Forensic entomology is the science of usinginsect evidence to determine informationrelated to a crime. By using insect evidencegathered from and around a corpse, a forensicentomologist can determine approximate time

Insect Body PlanInsects are primarily a terrestrial group, and aquatic insects proba-bly had terrestrial ancestors. Although the great majority of insectsare small (some are only a few centimeters in length), others aremuch larger. The African Goliath beetle, for example, exceeds 10cm (4 in.) in length. Generally, the larger insects live in tropicalareas. Despite great variation in their size, all insects share thesame general body plan, made up of three body sections.

1. Head. Located on an insect’s head are mandibles, specializedmouthparts, and one pair of antennae. The mandibles and mouth-parts of different insect species are adapted for eating differentfoods, as shown in Figure 11. In addition, an insect’s head usuallyhas a relatively large pair of compound eyes and a pair of antennae.Like the mouthparts, antennae vary greatly in size and shape.

2. Thorax. The thorax is composed of three fused segments.Attached to the thorax are three pairs of jointed walking legs.Some insects, such as fleas, lice, and silverfish, lack wings, butother adult insects have one or two pairs attached to the thorax.

3. Abdomen. The abdomen is composed of 9 to 11 segments. Inadult insects, there are no wings or legs attached to the abdomen.

Turn the facing page to learn more about one particular insect,the grasshopper, in Up Close: Eastern Lubber Grasshopper.

Organizing InformationThe numbered list on thispage lists three importantcharacteristics of insects.Use this information to drawa concept map that summa-rizes insect characteristics.

The mouthparts of the different insect species are adapted for different functions.

Figure 11 Insect mouthparts

MandibleMandible

Mandible

Grasshopper(adapted for biting and chewing)

Mosquito(adapted for piercing and sucking)

Fly(adapted for sponging and lapping)

674

Student Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TEKS Bio 7B, 8C

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 6D, 8C TAKS Obj 3 Bio 7B TAKS Obj 5 IPC 4ATEKS Bio 3D, 3F, 6D, 7B, 8B, 8C TEKS Bio/IPC 2C, 2D

pp. 674–675

Teaching TipSilk Encourage students toresearch the history of the discov-ery of silk. The Chinese were thefirst to produce silk fabrics, and forabout 3,000 years, they were theonly people who knew how to cul-tivate silkworms. Chinese legendscolorfully tell of the discovery ofsilk by Emperor Huangdi’s wife inabout 2700 B.C. Have studentscreate a poster or diorama of thehistory of silk.

Teaching TipMetamorphosis Ask students tocompare complete and incompletemetamorphosis in a GraphicOrganizer similar to the one at thebottom of this page. Students mayuse either generalizations or spe-cific insects in their comparisons.

Visual

Interpreting Visuals Tell studentsthat each visual in Figures 12 and13 depicts a cycle. Since there is nobeginning or end in a cycle, the stu-dent may choose any point to beginanalyzing the cycle. However, whencomparing two cycles, tell studentsto choose an equivalent point ineach to begin, such as the adult, tomake the comparison easier.TAKS 1 Bio/IPC 2C, 2D

GENERALBUILDERSKILL

TAKS 1 Bio/IPC 2C, 2DLS

Bio 3F


Graphic Organizer

Use this graphic organizer with TeachingTip: Metamorphosis on this page.

AdultPupaComplete metamorphosis

Incomplete metamorphosis

Egg Larva

Egg AdultNymph

Insect Life CycleThe life cycles of most insects are complex, and often several moltsare required before the adult stage is reached. During the last molt, the young insect undergoes a dramatic physical change called

.

Complete Metamorphosis Almost all insect species undergo “complete” metamorphosis, as shown in Figure 12. In complete meta-morphosis, the wingless, wormlike larva encloses itself within aprotective capsule called a (KRIHS uh lihs). Here, it passesthrough a stage, in which it changes into an adult.

A complete metamorphosis is a complex life cycle. The larvaecan, however, exploit different habitats and food sources thanadults. For example, the larvae ofnectar-drinking butterflies are cater-pillars that eat leaves! This ecologicalseparation of young from adults elimi-nates competition. This increases thechance of survival for each phase ofthe life cycle.

Incomplete Metamorphosis A smallernumber of species develop into adultsin a much less dramatic incompletemetamorphosis, as shown in Figure 13.In these species, the egg hatches into ajuvenile, or (NIHMF), thatlooks like a small, wingless adult. Afterseveral molts, the nymph develops intoan adult.

nymph

pupachrysalis

metamorphosis

Figure 12 Completemetamorphosis. A completemetamorphosis includes apupa stage, which is passedinside a chrysalis.

Adult emergingfrom chrysalis

Adult

Egg

YounglarvaOlder

larva

Pupa in chrysalis

Nymph

Nymph

Adult

Eggs

Nymph

Figure 13 Incompletemetamorphosis. The nymphpasses through several moltsbefore it becomes an adult.

675

Romance and the Grasshopper Almosteveryone knows that grasshoppers producesounds that resemble chirping “songs.” Butmost people don’t know that it is generallymale grasshoppers that play these songs as partof their courtship behaviors. They generallyhave a repertoire of three. The male grass-hopper’s initial song attracts the female, and

when a female comes close, the male plays amore “intimate” melody. However, whenanother male is close by and competing for the female, the male plays the rivalry song.Some females play no songs in response, whilethe females of some species respond with shortbursts of song. Bio 11B


Eastern LubberGrasshopper

Teaching Strategies Havestudents look up grasshoppersin field guides that are used forinsect identification. Ask themto compare the external struc-tures of the eastern lubbergrasshopper with those ofother grasshoppers. (The east-ern lubber grasshopper is ashort-horned grasshopper. Long-horned grasshoppers, such askatydids and Mormon crickets,have long, threadlike antennae.)Ask students to list the parts ofthe digestive system that helpto physically break down foodas well as the parts that chemi-cally break down food.(Physical digestion is performedby the labrum, labium,mandible, maxilla, and gizzard.Chemical digestion is performedby the midgut and coelom.)

Up Close

Up CloseEastern LubberGrasshopper

Scientific name: Romalea microptera

Size: 5 cm (2 in.) to 6.5 cm (2.6 in.) in length

Range: Eastern United States

Habitat: Fields and meadows

Diet: Grasses and other leafy vegetation

●

●

●

●

●

External Structures

Thorax The thorax is composed of

three fused segments, each with a pair

of legs. The front two pairs are walking

legs. The rear pair is larger jumping legs.

During mating season, males “sing” to

potential mates by rubbing a row of pegs

on a jumping leg against ridges on

a forewing.

Maxilla

Walkingleg

Abdomen

▲ Flying wing

Jumping leg

Ovipositor

Head

Antenna

OcellusCompound

eye

MandibleLabrum

▲ Forewing

Head Two antennae contain

sense organs for touch and smell.

On each side of the head is a very

large compound eye. Located

high on the forehead are three

light-detecting ocelli.

Wings Grasshoppers

have a pair of leathery

forewings that protect the

more delicate flying wings.

▼ Spiracles

Spiracles Spiracles admit air to the

extensively branching system of tracheae

that deliver oxygen throughout the body.

Mouthparts The stiff

upper labrum and lower

labium (lips) hold a leaf or

blade of grass in place while

the mandibles (jaws), assisted

by maxillas (graspers), tear

off pieces of the plant.

▼

Thorax

▼

▼ Mouthparts Labium

676

TAKS 1; TAKS 2; TAKS 3TAKS 1 Bio/IPC 2C, 2D; TAKS 2 Bio 8C, 10A; TAKS 3 Bio 7B

Student Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B TEKS Bio 7B, 8C, 10ATEKS Bio/IPC 2C, 2D

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B TEKS Bio 3F, 5A, 7B, 8C, 10A, 11BTEKS Bio/IPC 2C, 2DTEKS IPC 8E

pp. 676–677

develop into a pupa and from which they willemerge as a moth. Silk farmers do not allowmost pupas to become moths, because a mothwill shatter the silk cocoon as it leaves. Instead,farmers kill most pupae and process the silkcocoons. First the cocoon is unwound. Thenseveral processes strengthen the threads. Finally,the thread is dyed and woven into fabric.Bio 3F, 5A; IPC 8E


did you know?Silk is an agricultural product. Today, silk is made with cultivated silkworms, usuallycaterpillars of the species Bombyx mori. Thesilk-making process begins as the female lays300 to 500 eggs on special paper provided bysilk farmers. The eggs develop into larvae.When the silkworm larvae are ready to beginmetamorphosis, they spin a cocoon made of onecontinuous silk thread, in which they will

Eastern LubberGrasshopperDiscussion• How do grasshopper eyes

make it almost impossible tosneak up on this insect?(Grasshoppers have compoundeyes on each side of their headand three light-detecting ocellion their forehead.)

• How can you tell that thisgrasshopper is a female fromits external structures? (Thisgrasshopper has ovipositors,which are used to deposit fer-tilized eggs.)

• What structures do grasshop-pers use to move slowly?How do they make quickescapes? (Grasshoppers usetheir walking legs to moveslowly. When they need toescape quickly, they use theirjumping legs or wings.)

• What are the three mainsections of a grasshopper’sbody, and what is a majorbody function that occurs ineach section?(The grasshopper has a head, a thorax, and an abdomen.Touching, smelling, seeing,and chewing occur in the head;walking and jumping occur inthe thorax; and respiration,reproduction, and excretionoccur in the abdomen.)

• What would happen if everygrasshopper were to freezeduring a cold winter? (Thespecies would continue to sur-vive because grasshopper eggsstay dormant in winter andhatch in the spring.)

Up CloseInternal Structures

Nervous system The nervous system is

composed of a major ventral nerve cord with

ganglia located in each body segment. Three

fused ganglia in the head serve as the brain.

Reproductive system The

female collects the male’s sperm in

a storage pouch called a seminal

receptacle. Later, the female digs a

hole using two pairs of pointed

ovipositors. As she releases the

eggs into the hole, they are

fertilized by the stored sperm.

Midgut

Hearts

Flying wing

Gizzard

Digestive system Chewed

food enters a storage pouch

called a crop and passes to the

gizzard, where it is shredded

and crushed. Food is digested in

the midgut, and food molecules

pass through the midgut wall

into the fluid of the coelom.

This fluid eventually enters the

circulatory system.

▼ Nerve cord

▼ Crop

▲ Dorsal blood vessel

Anus

Ganglia

Malpighiantubules

Mouth

▲ Seminal receptacle

Circulatory system A long blood

vessel with a series of muscular “hearts”

runs along the grasshopper’s back. Blood

is pumped out of the open system and

bathes the body tissues directly before

returning to the heart.

Salivarygland

Brain

677



Analyzing theEffects of Pesticide UseSkills AcquiredReading graphs, inter-preting information

Teacher’s Notes Ask students to name all thepesticides they can. Discussthe problems associated withtheir use.

Answers to Analysis1. Populations were stable during

the first 4 years. Both popula-tions cycled between the samehigh and low values each year.

2. As the population of the bene-ficial species increases, pestnumbers decrease, and viceversa.

3. The number of beneficial speciesand insect pests decreased. Thepest population eventuallyrecovered and further increased.The beneficial species popula-tion did not recover.

4. Before the application of pesti-cide, the pest populationreached an annual maximumof about 6,000 per hectare.After the pesticide application,the pest population rose to10,000 per hectare.

5. Answers will vary.

010001011001110101000100100010011100100100010000010100100111010101001000101010010010

Pest control Invite a pest-control authority to class to discuss the problems and risksassociated with termites and other commonhousehold pests, such as ants and cockroaches.Ask the visitor to explain when such insects are considered a hazard. Have students askquestions about new methods used to controlpests and about how to avoid infestations.Bio/IPC 3C

REAL WORLDREAL WORLDCONNECTIONCONNECTION GENERAL

FlightInsects were the first animals to have wings. For more than 100 mil-lion years, until flying reptiles appeared, insects were the only flyingorganisms. Flight, illustrated in Figure 14, was a great evolutionaryinnovation. Flying insects were able to reach previously inaccessiblefood sources and to escape quickly from danger.

An insect’s wings develop from saclike outgrowths of the bodywall of the thorax. The wings of adult insects are composed entirelyof chitin, strengthened by a network of tubes called veins (whichcarry air, not blood). In most insects, the power stroke of the wingduring flight is downward, and it is produced by strong flightmuscles. When at rest, most insects fold their wings over theirabdomen, but a few insects are unable to do this. Dragonflies, forexample, keep their wings outstretched when they rest beside apond. Most insects have two pairs of wings. A few groups of insects,such as fleas and lice, are wingless.

In most insects only one pair of wings is functional for flight. Insome species, the second pair of wings serves another purpose. Forexample, in grasshoppers and beetles, the forewings act as protec-tive wing covers. In flies, the hindwings are modified into knoblikestructures that help control stability during flight.

Figure 14 Insect flight.This stop-action series showshow this insect’s wings moveduring flight.

Analysis

1. Identify the years during which thetwo insect populations appear tomaintain stability in relation to eachother. Justify your answer with datafrom the graph.

2. Describe the relationship betweenthe two insect species before year 4.

3. Describe the changes in the twopopulations after the use of a pesticide.

4. Compare the annual changes in population size of the pest species before and after the use of a pesticide.

5. Critical Thinking DevelopingHypotheses Propose a hypothesisthat might explain the dramaticchanges that occur in the insect popu-lations after the use of pesticides.

Analyzing the Effects of Pesticide UseBackground

In nature, insect pests are usually kept in balance by the presence of predators, includingother insects. The use of some pesticides can upset this balance, as shown in the graphbelow. Examine the graph, and answer the analysis questions.

010001011001110101000100100010011100100100010000010100100111010101001000101010010010

Popula

tion s

ize (1

,000

s p

er a

cre)

2

4

6

8

10

0 1 2 3 4 5 6

Time (years)

Changes in Two Insect Populations

Insect pest Beneficial species

Pesticide application

2C 2D 12B

678

TAKS 1, TAKS 3

TAKS 1 Bio/IPC 2C, 2D; TAKS 3 Bio 12B

Student Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 12B TEKS Bio 7B, 8B, 8C, 11B, 12BTEKS Bio/IPC 2C, 2D

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 8C, 10ATAKS Obj 3 Bio 7B, 12B TAKS Obj 5 IPC 4A TEKS Bio 7B, 8B, 8C, 10A, 11B, 12BTEKS Bio/IPC 2C, 2D, 3CTEKS IPC 4A

pp. 678–679 IPC Benchmark Fact

Review the concepts of work (work � force �distance) and power (power � power/time) by havingstudents calculate and compare the work and powerdone in flight by two imaginary lacewings. For exam-ple, assume that during its flight lacewing A exerted aforce of 2 N over a distance of 10 m in 4 s whilelacewing B exerted a force of 3 N over a distance of15 m in 10 s. Remind students that the joule (N-m) isthe work unit and watt (J/s) is the power unit. Ask stu-dents which lacewing did the most work and whichone had the highest power output. TAKS 5 IPC 4A

Answers to Section review

1. The Eastern Lubber grasshopper has a bodyplan like that of a typical insect. It has a head,a thorax, and an abdomen; three pairs ofjointed legs; antennae; and an exoskeleton.

2. Grasshoppers go through several nymph stagesduring incomplete metamorphosis. Butterfliesgo through complete metamorphosis, with egg,larva, pupa, and adult stages.

3. Insects have three body sections, three pairs oflegs, and antennae; millipedes have many bodysegments with two pairs of legs per segment,and are herbivores; centipedes have many body

Bio 8B

TAKS 2 Bio 8C; Bio 8B

segments with one pair of legs per segment,and are carnivores.

4. Wings are the key characteristic in classification.They are described for each class.

5. A. Correct. Two antennae contain sense organs for touch and smell. B. Incorrect. Grasshop-pers’ antennae containsense organs for touch but not hearing. C. Incorrect. Grasshoppers see with compoundeyes, not their antennae. D. Incorrect.Grasshoppers’ antennae contain sense organsfor touch, but they see with their compoundeyes. TAKS 2 Bio 10A; Bio 11B

TAKS 2 Bio 8C

TAKS 2 Bio 8C

Teaching TipBees in Agriculture Tell studentsthat the widespread use of pesticidesprays has resulted in the loss ofbeehives. Have students discuss theeffects the loss of these hives mighthave on consumers. (Because beesare needed to pollinate many crops,reduced agricultural production andhigher prices would result.) Tell stu-dents that some farmers have to rentmobile beehives to pollinate theircrops.

ReteachingDivide the class into four groups.Write the name of each of the fourinsect orders listed in Table 1 onslips of paper. Have a representa-tive from each group pick one ofthe folded slips out of a bowl orbeaker, making sure they cannotsee the writing on the slips. Thenhave each group ask questions ofthe other groups about insects intheir order. The questions shouldbe phrased so that they can beanswered “yes” or “no.”

Interpersonal

Quiz1. List the structures usually found

on the insect head. (mandibles,specialized mouth parts, andantennae)

2.What is the relationship betweeninsects and centipedes? (Insectsand centipedes are both arthro-pods in the Subphylum Uniramia.However, they belong to differentClasses.)

AlternativeAssessmentCollect a variety of images ofinsects, centipedes, and millipedesfrom nature magazines, the Web, orother resources you may have. Havestudents work in groups of threeand distribute the images equallyamong the groups. Have studentsdevelop twenty questions (andanswers) about their images. Usingtheir images and the questions theydeveloped, have groups quiz eachother.TAKS 2 Bio 8C; TAKS 3 Bio 7B

TAKS 1 Bio/IPC 2C, 2D;

GENERAL

TAKS 2 Bio 8C

TAKS 2 Bio 10A

GENERAL

TAKS 3 Bio 7B; Bio 8BTAKS 1 Bio/IPC 2C, 2D; LS

CloseClose

TAKS 1 Bio/IPC 2D; Bio/IPC 3C

GENERAL


Social InsectsTwo orders of insects, Hymenoptera (ants, bees, andwasps) and Isoptera (termites), have elaborate socialsystems. These insects often live in highly organizedsocieties of genetically related individuals. Withinthese insect societies, there is a marked division oflabor, with different kinds of individuals performingspecific functions. The role played by an individual ina colony is called its . Caste is determined by acombination of heredity; diet, especially as a larva;hormones; and pheromones, chemical substancesused for communication. In the termite colony shownin Figure 15, for example, small, active members called workersgather the food, raise the young, and excavate tunnels. Other, largertermites, called soldiers, defend the colony with their immense jaws.Both workers and soldiers are sterile. Reproduction is a function ofonly the queen and king.

Insect RelativesCentipedes and millipedes, shown in Figure 16, have similar bodies.Each has a head region followed by numerous similar segments.Each segment bears one or two pairs of legs. Centipedes have onepair of legs per segment and can have up to 173 segments. Modernmillipedes have from 11 to 100 or more body segments, and mostmillipede segments have two pairs of legs. While centipedes arecarnivores, most millipedes are herbivores.

caste

Figure 16 Centipedes andmillipedes. Centipedes arecarnivorous predators, whilemillipedes are herbivores thatfeed on decayed vegetation.

Figure 15 Termite colony.Most of the members of thistermite colony are unable toreproduce. The queen, withher enormous abdomen, is the egg-laying machine of the colony.

Centipede Millipede

Section 3 Review

Relate the Eastern Lubber grasshopper’s bodyplan to that of a typical insect. 8B 8C

Compare the life cycles of grasshoppers andbutterflies. 8B

Identify the distinguishing characteristics ofinsects, millipedes, and centipedes. 8C

Critical Thinking Forming HypothesesBased on the information given in Table 1, whatcharacteristic is key to determining an insect’sclassification? Support your answer. 8C

A grasshopper’s antennaecontain sense organs for A touch and smell. C hearing and vision.B smell and hearing. D vision and touch.

TAKS Test PrepTAKS Test Prep10A 11B

679

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. Section 4 focuses on crus-taceans. This section first describesterrestrial crustaceans, such as pillbugs, sow bugs, sand fleas, andland crabs. Next, Section 4 dis-cusses aquatic crustaceans, such ascrabs, lobsters, shrimps, and cray-fish. The section ends with the storyof sessile crustaceans, the barnacles.

Invite students to name as manycrustaceans as they can. If theyhave difficulty, suggest that theythink about crustaceans they mayhave seen in seafood restaurantsand aquaria.

DemonstrationBring in a few crayfish in a bucketfor students to observe. Have stu-dents predict how the crayfish willmove if a stick is suddenly placed in front of them. Students may besurprised when the crayfish shootoff backwards. Have studentsobserve the crayfish’s movementsfor several minutes. VisualTAKS 1 Bio/IPC 2C, 2D

LS

GENERAL

MotivateMotivate


Bellringer

FocusFocus

Section 4


• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Data Lab• Data Sheet for Data Lab GENERAL

GENERAL

GENERAL

GENERAL

Chapter Resource File Transparencies

TT BellringerTT Comparing Crustaceans and Insects

• Reading Organizers• Reading Strategies

Planner CD-ROM

Section 4 Crustaceans

Crustacean HabitatsJust as insect species dominate on land, crustaceans abound in theworld’s oceans. Their great numbers have earned them the nick-name “the insects of the sea.” Many are microscopic creatures thatdrift as plankton in the ocean currents. While primarily marine,members of subphylum Crustacea are also found in fresh water andin a few terrestrial habitats. Crustaceans include crabs, lobsters,crayfish, shrimps, barnacles, water fleas (Daphnia), and pill bugs.

Almost all crustaceans have a distinctive larval form called a(NAW plee uhs). The nauplius, shown in Figure 17, has

three pairs of branched appendages. Like insects, the naupliusundergoes a series of molts before it takes on its adult form.

Adult crustaceans also have mandibles, as insects do. But crus-taceans differ from insects in a number of important respects, assummarized in Table 2.

Terrestrial Crustaceans Only a few crustacean groups have successfully invaded terrestrialhabitats. The most widespread group of terrestrial crustaceans iscomposed of the pill bugs and sow bugs. They live among leafyground litter found in gardens and woods. Pill bugs and sow bugsbelong to a group called isopods and are the only crustaceans thatare truly terrestrial. Another group, the sand fleas, includes severalthousand species typically found along beaches. In addition, a fewspecies of land crabs live in damp areas. Land crabs are only partlyadapted to terrestrial living. They are active primarily at night,when the air is more moist. Their life cycle is tied to the ocean,where the larvae live until maturity.

nauplius

Objectives● Summarize how

crustaceans and insects aresimilar and dissimilar.

● Describe the body plan ofdecapods.

Key Terms

naupliuskrill

Eye Appendages

Figure 17 Nauplius.A microscopic, free-swimming nauplius larva isa developmental stage ofalmost all crustaceans.

www.scilinks.orgTopic: CrustaceansKeyword: HX4054

Table 2 Comparison of Crustaceans and Insects

Antennae Two pairs One pair

Location of Cephalothorax Head and abdomenappendages and abdomen

Chewing Usually three pairs One pairappendages

Nature of Most are branched Unbranchedappendages at the end at the end

Insects

Respiration Gills Tracheal system

Characteristic Crustaceans

8C

8C

680

Student Edition TAKS Obj 2 Bio 8C TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 7B TEKS Bio 7B, 8C, 10A

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2DTAKS Obj 1 IPC 3ATAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B, 12BTEKS Bio 3A, 3F, 5B, 7B, 8C, 10A, 11DTEKS Bio/IPC 2C, 2D TEKS Bio/IPC 3A

pp. 680–681

TAKS 2

TAKS 2

Teaching TipHealth Some crabs have beenfound to carry human parasites. InAsia, freshwater crabs can carrylung flukes, which can then betransmitted to humans who eat thecrabs. In Africa, onchocerciasis, aneye disease that is transmitted byflies, is also carried on the backs ofriver crabs, where the fly larvaelive. However, most decapods arenot harmful to people when theyare cooked properly. Students inthe United States are often unawareof diseases that afflict people incountries that do not have effectivepublic health systems. Encouragestudents to find out more aboutthese parasitic diseases.TAKS 1 Bio/IPC 2D; IPC 3A; Bio 3A, 11D

GENERAL

TeachTeach


did you know?How the fiddler crab got its name. Themale fiddler crab has one large cheliped(pincer) and one small one. The male waves its large cheliped back and forth, much likeplaying a fiddle, when it is in the presence of a female. Bio 3F

MISCONCEPTION ALERT

Pill Bugs Although their name impliesotherwise, pill bugs or potato bugs areactually terrestrial crustaceans, not insects.Pill bugs belong to the Order Isopoda (theisopods). Whereas insects have three pairsof legs and breathe with a system of tra-cheae, pill bugs have seven pairs of legs andbreathe with gills.TAKS 1 Bio/IPC 2D; TAKS 2 Bio 8C

Aquatic CrustaceansCrustaceans are a major food source for humans andsome animals. The members of some orders of crus-taceans are quite small. Common are fairy shrimps,water fleas, ostracods, and tiny copepods (KOH puhpahds). Copepods are among the most abundant multi-cellular organisms on Earth and are a key food source inthe marine food chain. Another small marine crustacean,Euphausia superba, swarms in huge groups and is knownby its common name, . Krill, shown in Figure 18, arethe chief food for many marine species.

DecapodsLarge marine crustaceans such as shrimps, lobsters, and crabs,along with the freshwater crayfish shown in Figure 19, have fivepairs of legs and are often referred to as decapods. Almost onequarter of all crustaceans are decapods. The head and thorax ofdecapods are fused into a single cephalothorax, which is covered ontop by a protective shield called a carapace.

In crayfish and lobsters, the anterior pair of legs are modifiedinto large pincers called chelipeds (KEE luh pehdz). Appendagescalled swimmerets are attached to the underside of the abdomenand are used in swimming and in reproduction. Flattened, paddle-like appendages called uropods are at the end of the abdomen.Many decapods have a telson, or tail spine. Decapods can propelthemselves through the water by forcefully flexing their abdomen.

krill

Figure 19 Crayfish

Figure 18 Krill. Found inicy Antarctic waters, krill are the favorite food of manymarine animals.

Antenna

Antennules

Cheliped

Walking legs

Cephalothorax

Abdomen

Telson

Uropod

Swimmerets

Like all decapods, the crayfish has five pairs of legs.

www.scilinks.orgTopic: Texas CrustaceansKeyword: HXX4012

681

Relating Moltingto Mortality RatesSkills AcquiredReading graphs, apply-ing information

Teacher’s NotesHave students infer what soft-shelled crabs are and when theyare most readily available inrestaurants.

Answers to Analysis1. Most crabs die in April, May,

and June.2. Most crabs molt in April, May,

and June.3. During their molting season,

many crabs fall prey to preda-tors and disease.

4. When the crabs molt, morewill die due to disease and predation.

5. Answers will vary. Crabs arefragile after molting and aremore susceptible to disease.

010001011001110101000100100010011100100100010000010100100111010101001000101010010010

TAKS 1 BioIPC 2C, 2D; TAKS 3 Bio 7B, 12B

ReteachingShow photographs of a lobster and a water flea, and ask studentsto identify the similarities anddifferences. Visual

QuizTrue or False:

1. Pill bugs and sow bugs are ter-restrial crustaceans, not insects.(True)

2.Lobsters and crabs are calleddecapods because they have fivepairs of legs. (True) TAKS 2 Bio 8C

TAKS 2 Bio 8C

GENERAL

TAKS 2 Bio 8C; TAKS 3 Bio 7BLS

CloseClose

Answers to Section Review

1. Answers should summarize the informationgiven in Table 2 of this section.

2. Decapods have antennae, pincers, acephalothorax with walking legs, and asegmented abdomen.

3. You would most likely find pill bugs only inmoist environments. Bio 11B

TAKS 2 Bio 8C

TAKS 2 Bio 8C4. A. Incorrect. Antennae work

well in terrestrial environments, sensing touchand smell. B. Correct. Gills allow organisms tobreathe in water. C. Incorrect. Walking legswork well in terrestrial environments and arenot very useful in aquatic environments. D. Incorrect. Mandibles work equally well in terrestrial and aquatic environments.TAKS 3 Bio 7B; Bio 12C


Sessile Crustaceans Barnacles are a group of crustaceans that are sessile as adults. Free-swimming larvae attach themselves to a rock, post, or someother submerged object, where they remain. Hard plates that canopen and close protect the barnacle’s body. When feeding, barnaclesextend their jointed feeding appendages (legs) through the openplates. Their feathery legs stir food from the water into the barnacles’mouth. Unlike most crustaceans, barnacles are hermaphrodites.However, they do not usually fertilize their own eggs.

Analysis

1. Summarize what the datain the graph tell you aboutcrab mortality.

2. Summarize what thegraph shows about moltingin crabs.

3. Describe the relationshipbetween the mortality ratesand molting periods of crabs.

4. Critical ThinkingDeveloping HypothesesPropose a hypothesis thatexplains the relationshipbetween the percent of crabsmolting and mortality rates.

5. Critical ThinkingMaking PredictionsMost states have laws thatrequire crab fishers to return

molting crabs to the water.How might the length oftime a molting crab isexposed to air or how

roughly a crab is handledaffect whether the crabsurvives being caught and released?

Relating Molting to Mortality RatesBackground

During the soft-shell stage that follows molting, many crustaceans die of diseaseor are eaten by predators. The bar graph below shows the percent mortality forcrabs over a 9-month period. Study the data, and answer the analysis questions.

010001011001110101000100100010011100100100010000010100100111010101001000101010010010

Jan

Feb

Mar

ch

Ap

ril

May

June

July

Aug

Sep

t0

5

15

10

20

3025

35

Molting and Mortality Data

Molt

and m

ort

alit

y data

(in p

erce

ntag

e of

pop

ulat

ion) In moltDisease Predation

Compare the body plan of a crustacean with thatof an insect. 8C

Describe the external body plan of a decapod.

Critical Thinking Making Predictions Pillbugs respire with gills. How might this affect thedistribution of pill bugs in an ecosystem? 11B

Section 4 Review

2C 2D 12B

8C

Which structures areadaptations of crustaceans to life in aquaticbiomes? 7B 12C

A antennae. C walking legs.B gills. D mandibles.


682

Student Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 12B TEKS Bio 7B, 8B, 8C, 11B, 12B, 12CTEKS Bio/IPC 2C, 2D

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B, 12B TEKS Bio 7B, 8C, 11B, 12B, 12CTEKS Bio/IPC 2C, 2D

pp. 682–683

TAKS 1,TAKS 3

AlternativeAssessmentHave students construct conceptmaps that show the similarities anddifferences among the followingarthropods: arachnids, insects,millipedes and centipedes, andcrustaceans. TAKS 2 Bio 8C; Bio 8B

GENERAL

Answer to Concept Map

The following is one possible answer toPerformance Zone item 15.


• Science Skills Worksheet• Critical Thinking Worksheet• Test Prep Pretest• Chapter Test GENERAL

GENERAL

GENERAL


with modified

complete metamorphosis

tracheae

cephalothorax

appendagesegg nymph adult egg larva pupa adult

spiracles

cheliceraepedipalpsnaupliuschrysalis

breathe using

develop through

body regions fuseforming a

crustaceans

incomplete metamorphosis

in

with

is a developswithin a

with

such as

Arthropods

Key Concepts

Study CHAPTER HIGHLIGHTS

ZONE

Features of Arthropods● All arthropods have a coelom, a segmented body, and

jointed appendages that are modified to perform differentfunctions.

● Arthropods have an exoskeleton made of chitin, which theydiscard periodically in a process called molting.

● Arthropods are grouped into three subphyla: Chelicerata,Uniramia, and Crustacea.

Spiders and Other Arachnids● Members of subphylum Chelicerata have mouthparts, called

chelicerae, that are modified into fangs or pincers. ● Spiders have a head and a cephalothorax, no antennae, six

or eight pairs of simple eyes, a pair of fangs and pedipalps,and four pairs of walking legs.

● Scorpions have pedipalps modified into large, graspingpincers. A stinger is located at the end of their abdomen.

● Mites have body parts that are fused to form an unseg-mented body. Many mites transmit diseases.

Insects and Their Relatives● Insects make up more than half of all named animal

species.● All insects have a body plan with three body sections (head,

thorax, and abdomen), three pairs of legs (all attached tothe thorax), and one pair of antennae.

● The life cycles of insects are complex and involve a processof change called metamorphosis, during which larvaechange into the adult insects.

Crustaceans● Crustaceans have a distinctive larval form called a nauplius.● Copepods and krill, which are tiny marine crustaceans, are

the chief food of many marine species.● Most crustaceans have branched appendages, two pairs of

antennae, three chewing appendages, walking legs attachedto the thorax, and gills. Like insects, crustaceans have jawscalled mandibles.

4

3

2

1

Key Terms

Section 1appendage (664)thorax (666)cephalothorax (666)compound eye (666)molting (668)trachea (668)spiracle (668)Malpighian tubule (669)

Section 4nauplius (680)krill (681)

Section 2chelicera (670)pedipalp (670)spinneret (670)

Section 3mandible (673)metamorphosis (675)chrysalis (675)pupa (675)nymph (675)caste (679)

683

ANSWERS

Using Key Terms

1. a2. b3. c4. b5. a. The cephalothorax is the head-

chest region of an arthropod;the exoskeleton is the hardouter covering of an arthropod.

b. Tracheae are breathing tubes;spiracles are breathing holes inthe exoskeleton.

c. Pedipalps catch and handleprey; spinnerets make silk.

d. Chelicerae are mouthparts ofarachnids; mandibles aremouthparts of uniramians andcrustaceans.

Understanding Key Ideas

6. c7. c8. d9. c

10. a11. d12. b13. a14. Monarch butterflies use either the

direction of the sun or the Earth’smagnetic field to navigate duringmigration.

15. The answer to the concept map isat the bottom of page 701.TAKS 1 Bio/IPC 2C; Bio 3E

Bio 11B

TAKS 3 Bio 12B, 12E; Bio 12DTAKS 2 Bio 8CTAKS 2 Bio 8C; Bio 8BTAKS 2 Bio 8CTAKS 2 Bio 8CTAKS 3 Bio 7BTAKS 2 Bio 8CBio 8B

TAKS 2 Bio 10ATAKS 2 Bio 8CTAKS 3 Bio 7BTAKS 2 Bio 10A

Section Questions1 5a, 6, 7, 8, 212 2, 3, 5, 7, 15, 17, 203 1, 4, 5, 9, 10, 11, 14, 15, 16, 17, 18, 19,

20, 224 12, 13, 15, 18, 21

Assignment Guide


CHAPTER 30

Using Key Terms1. The chief organ of excretion in insects

is the 10Aa. Malpighian tubule.b. pedipalp.c. nephridium.d. spiracle.

2. In spiders, chelicerae are modified into a. spinnerets. c. legs.b. fangs. d. antennae.

3. Spinnerets are located on the spider’s 8Ca. thorax. c. abdomen.b. cephalothorax. d. pedipalps.

4. Insects respire through structures called 10Aa. book lungs. c. gills.b. spiracles. d. ganglia.

5. For each pair of terms, explain the differ-ences in their meanings.a. cephalothorax, exoskeletonb. tracheae, spiraclesc. pedipalps, spinneretsd. chelicera, mandible

Understanding Key Ideas6. What evidence suggests that arthropods

are closely related to annelids? 8Ba. Arthropods and annelids have gills.b. Both groups have marine species.c. Segmentation is present in both groups.d. Arthropods have vestigial parapodia.

7. Which is a feature of the arthropod body plan? 8Ca. a hydrostatic support systemb. pharyngeal slitsc. an exoskeletond. a nonsegmented body

8. Arthropods molt because 7Ba. their body grows faster than their shell.b. of damage to their exoskeleton.c. their exoskeleton cracks and lets in

water. d. their hard exoskeleton cannot grow

larger.

9. In adult insects 8Ca. the abdomen has wings.b. there are two pairs of antennae.c. the legs are attached to the thorax.d. the first appendages are chelicerae.

10. Which of the following sequences shows acomplete metamorphosis? 8Ca. egg → larva → pupa → adultb. egg → larva → adultc. egg → young juvenile → older juveniled. egg → pupa → winged juvenile → adult

11. Millipedes and centipedes differ in thatmillipedes 8B 8Ca. are terrestrial and segmented.b. have one pair of legs on each segment.c. have poisonous fangs.d. are herbivores.

12. Which of the following is not a crustacean? 8Ca. lobster c. copepodb. scorpion d. water flea

13. Copepods are said to be the most importantanimals on Earth because they area. a critical link in the marine food chain.b. found in both the ocean and fresh water.c. accomplished predators.d. easier to collect and study than other

arthropods.

14. Why is Earth’s magneticfield important to Monarch butterflies? 11B

15. Concept Mapping Construct aconcept map that outlines the three majorgroups of arthropods and that gives thecharacteristics for each group. Try to include the following terms in your concept map: appendages, cephalothorax,tracheae, spiracles, chelicerae, pedipalps,complete metamorphosis, chrysalis, pupa,and nauplius. 2C 3E

PerformanceZONE

CHAPTER REVIEW

7B

12B 12D 12E

684

Review and AssessTAKS Obj 1 Bio/IPC 2CTAKS Obj 2 Bio 8C, 10ATAKS Obj 3 Bio 4C, 4D, 7B, 12B, 12ETEKS Bio 3D, 3E, 7B, 8B, 8C, 11B,11D, 12B, 12D, 12E

pp. 684–685

Critical Thinking

16. A species that undergoes com-plete metamorphosis wouldprobably have the advantage. In complete metamorphosis, thelarvae have different food sourcesfrom the adults, and this differ-ence might help one or the othersurvive. Also, during completemetamorphosis, the pupa iswithin a protective chrysalis andwould likely survive the drought.In incomplete metamorphosis,the nymph is similar to the adult,and both nymphs and adultswould likely be affected.

17. Spiders eat insects. When spidersare removed, insects have fewerpredators. Killing the spidersprobably led to an increase in theinsect population.

18. It is an insect because it has threecommon insect characteristics.

19. Predators might think the moth isa snake and therefore not attack it.

Alternative Assessment

20. Models will vary but shouldshow the external structures illus-trated in the drawings of thespider or grasshopper depicted in the Up Close features in thischapter.

21. Answers will vary, but brochuresshould be well organized andpresent the group’s findingsaccurately.

22. Answers will vary. Agriculturalinsect inspectors work for cropproducers to identify harmful andhelpful insects. A college degreein entomology may be required.Employers include agriculturalstations, universities, and govern-ment agencies. Growth prospectsare good. Starting salary willvary by region. Bio 3D

TAKS 3 Bio 4C, 4D, 12B; Bio 11D

Bio 3E

TAKS 3 Bio 7B

TAKS 2 Bio 8C

TAKS 3 Bio 12E

TAKS 3 Bio 7B; Bio 12D

1. A. Incorrect. Touch is detected by thegrasshopper’s antennae. B. Incorrect. Sound isnot detected in the grasshopper by structure A.C. Correct. Structure A is an ocellus, a light-detecting organ of the grasshopper. D. Incorrect.Smell is detected by the grasshopper’s antennae.

2. F. Incorrect. Air enters and leaves the grasshop-per through the spiracles. G. Correct. Themandibles and the maxillas are used to biteand chew leaves. H. Incorrect. The grasshopper

Bio 11B

has no structures for sponging and lappingliquids. J. Incorrect. Grasshoppers are herbi-vores and do not catch and handle prey.

3. A. Incorrect. The exoskeleton is hinged at thejoints for movement. B. Incorrect. Grasshoppersdo not inhabit deep water. They are terrestrial.C. Correct. The exoskeleton is efficient in conserving body moisture. D. Incorrect. Theexoskeleton does not grow; grasshoppers moltto allow for growth. TAKS 2 Bio 10A

TAKS 3 Bio 7B


Critical Thinking16. Applying Information If levels of vegeta-

tion were reduced, which arthropodspecies would likely have a greater advan-tage—an arthropod species that undergoescomplete metamorphosis or one thatundergoes incomplete metamorphosis?Explain your answer.

17. Recognizing Logical InconsistenciesA neighbor commented that there was anincreased number of insects around herhouse and that she was killing every spidershe saw. How might these actions affect thenumber of insects around a house?

18. Inferring Conclusions An unknown arthro-pod has three body segments, one pair ofantennae, and three pairs of jointed legs.What kind of arthropod is it? Explain howyou arrived at this conclusion.

19. Recognizing Relationships The wings of theatlas moth, Attacus atlas, look much like thehead of a snake. Why might it benefit a fly-ing insect to look like a snake?

Alternative Assessment20. Forming a Model Using papier mâché or

some other material, make a model of agrasshopper or a spider. Decide in advancehow many features of insects you mustshow to make an adequate model. Presentyour model to the class, and describe thestructures that you modeled.

21. Communicating Information Use the mediacenter or Internet sources to learn moreabout diseases transmitted by arthropods.Develop a brochure that presents yourfindings. The brochure should discuss thespecies that transmit the disease, as well asthe symptoms and treatment of the disease.

22. Career Connection Agricultural InsectInspector Research the field of inspectingfield crops for the presence of harmfulinsects, and write a report on your findings.Your report should include a job descrip-tion, training required, kinds of employers,growth prospects, and starting salary.

Use the illustration below and your knowledgeof science to answer questions 1–3.

1. What type of environmental stimulus isstructure A sensitive to?A touch C lightB sound D odor

2. Structures B and C are specialized for F inhaling and exhaling air.G biting and chewing leaves. H sponging and lapping liquids.J catching and handling prey.

3. This animal’s exoskeleton is adapted to A prevent movement at the joints.B withstand pressure in deep water.C help prevent water loss.D grow as the animal grows.


7B

11B

10A

3E7B 12D

12E

8C

7B

4C 4D 11D 12B

3D

A

B

C

TestIf points are not deducted for guessing, answerevery question.

685

section 1 features of arthropods

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