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

Assessment Resources Additional Resources

Index to National Geographic MagazineThe following articles may be used forresearch relating to this chapter:“Money From the Sea,” by Phil Nuytten,January 1993.“The Pearl,” by Fred Ward, August 1985.“My Chesapeake—Queen of Bays,” by AllanC. Fisher, Jr., October 1980.

Teacher’s Corner

Mollusks and Segmented Worms

Mollusks and Segmented Worms

TransparenciesReproducible MastersSection

Mollusks

SegmentedWorms

Section 27.1

Section 27.2

Teacher Classroom Resources

Reinforcement and Study Guide, pp. 119-121BioLab and MiniLab Worksheets, p. 121Laboratory Manual, pp. 191-198Content Mastery, pp. 133-134, 136

Reinforcement and Study Guide, p. 122Concept Mapping, p. 27Critical Thinking/Problem Solving, p. 27BioLab and MiniLab Worksheets, pp. 122-124Content Mastery, pp. 133, 135-136 L1

P

LS

L2

P

LS

L3

P

LS

P

ELL

LS

L3

P

LS

L2

P

LS

L1

P

LS

L2

P

LS

L2

P

LS

L2

P

LS

Section Focus Transparency 67Basic Concepts Transparency 48Reteaching Skills Transparency 40

Section Focus Transparency 68

P

ELL

LS

L1

P

LS

P

ELL

LS

L1

P

LS

P

ELL

LS

L2

P

LS

P

ELL

LS

L1

P

LSAssessment Resources Additional ResourcesSpanish ResourcesEnglish/Spanish AudiocassettesCooperative Learning in the Science ClassroomLesson Plans/Block Scheduling

COOP LEARN

LS

P

ELL

LS

P

ELL

LS

Chapter Assessment, pp. 157-162MindJogger VideoquizzesPerformance Assessment in the Biology ClassroomAlternate Assessment in the Science ClassroomComputer Test BankBDOL Interactive CD-ROM, Chapter 27 quiz

Chapter 27 OrganizerChapter 27 Organizer

Activities/FeaturesObjectivesSection

MollusksNational Science EducationStandards UCP.1, UCP.2,UCP.3, UCP.5; C.4, C.5, C.6(1 session, 1/2 block)

Segmented WormsNational Science EducationStandards UCP.1, UCP.2,UCP.4, UCP.5; A.1, A.2; C.3,C.5, C.6; E.1, E.2; F.6; G.1,G.3 (2 sessions, 1 block)

1. Identify the characteristics of mollusks.2. Compare the adaptations of gastropod,

bivalve, and cephalopod mollusks.

3. Describe the characteristics of seg-mented worms and their importance tothe survival of these organisms.

4. Compare and contrast the classes ofsegmented worms.

Inside Story: A Clam, p. 743Problem-Solving Lab 27-1, p. 744MiniLab 27-1: Identifying Mollusks, p. 746

Problem-Solving Lab 27-2, p. 749MiniLab 27-2: A Different View of anEarthworm, p. 750Inside Story: An Earthworm, p. 751Careers in Biology: Microsurgeon, p. 752Design Your Own BioLab: How do earth-worms respond to their environment? p. 754Earth Science Connection: Mollusks asIndicators, p. 756

Section 27.2

Section 27.1

MATERIALS LIST

BioLabp. 754 live earthworms, paper towels,glass pan, sandpaper, culture dishes,thermometer, hand lens or stereo-microscope, dropper, penlight, ice,metric ruler, black paper, cotton swabs

MiniLabsp. 746 dichotomous key transparency,overhead projector, marine shellsp. 750 cross-section diagrams of earth-worm, longitudinal diagrams of earth-worm

Alternative Labp. 744 land snails, clear plastic delitrays, wax marking pencil, lamp with60-watt bulb, crushed ice, ring stand,black paper, sandpaper, metric ruler

Quick Demosp. 742 land snail, petri dish, pencil, lettucep. 742 whole squid, knife

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

740A 740B

Key to Teaching StrategiesKey to Teaching Strategies

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

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

L1

P

LS

L2

P

LS

L3

P

LS

P

ELL

LS

P

COOP LEARN

LS

PP

LS

P

LS

The following multimedia resources are available from Glencoe.

Biology: The Dynamics of LifeCD-ROM

Exploration: MollusksBioQuest: Biodiversity ParkExploration: The Five Kingdoms

Videodisc ProgramScallop Escape

The Infinite VoyageTo the Edge of the Earth

The Secret of Life SeriesMulluscan Body PlanEarthwormEarthworm Segment

P

LS

P

ELL

LS

Section

What Is a Mollusk?Slugs, snails, and animals that once

lived in shells in the ocean or on the beach are all mollusks. Theseorganisms belong to the phylumMollusca. Members of this phylumrange from the slow moving slug tothe jet-propelled squid. Althoughmost species live in the ocean, otherslive in freshwater and moist terres-

trial habitats. Some aquatic mollusks,such as oysters and mussels, livefirmly attached to the ocean floor orto the bases of docks or woodenboats. Others, such as the octopus,swim freely in the ocean. Land-dwelling slugs and snails can befound crawling slowly over leaves onthe forest floor.

Examples of three classes of mol-lusks are shown in Figure 27.1.

If you are a shell collector, a walkon the beach as high tide begins torecede can reveal bountiful trea-

sures. The shell sizes, shapes, and col-ors are clues to the many differentkinds of animals that once inhab-ited these structures. How couldthe marine animal that lived inthe fan-shaped shell be relatedto the common garden slug?

SECTION PREVIEW

ObjectivesIdentify the character-istics of mollusks.Compare the adapta-tions of gastropod,bivalve, and cephalopodmollusks.

Vocabularymantleradulaopen circulatory systemclosed circulatory system nephridia

27.1 Mollusks

Figure 27.1With 100 000 describedspecies, phylum Molluscais second in size only toinsects and their relatives.

OriginWORDWORD

molluskFrom the Latinword molluscus,meaning “soft.” Mollusks are animalswith two body open-ings, a muscularfoot, and a mantle.

Shells (above)and a gardenslug (inset)

Snails, slugs, their shell-less relatives, andother one-shelledanimals such asthis limpet makeup the largestclass of mollusks.

AA

Oysters, clams, and scallopssuch as this one have two hinged shells.

BB

Predatory squids andoctopuses are mollusksthat do not have anexternal shell.

CC

741

Section 27.1

BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Use with Chapter 27,Section 27.1

How would you classify these mollusks into three groups?

What characteristics do the animals in each group share?

11

22

Transparency Mollusks67 SECTION FOCUS

Cop

yrig

ht ©

Gle

ncoe

/McG

raw

-Hill

, a d

ivis

ion

of T

he M

cGra

w-H

ill C

ompa

nies

, Inc

.

Snail

Slug

Nudibranch Clam

Nautilus

Octopus

Oyster

PrepareKey ConceptsStudents will study the generalcharacteristics of mollusks andthe traits that distinguish organ-isms in the three mollusk classes.

Planning■ Gather assorted sea shells for

the Getting Started Demo.■ Order live land snails and pur-

chase squid and live clams forthe Quick Demos, Portfolio,and the Alternative Lab.

■ Purchase surgical gloves forthe Building a Model.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 67 on the overhead pro-jector and have students answerthe accompanying questions.

P

ELL

LS

L1

P

LS

Assessment PlannerAssessment PlannerPortfolio Assessment

Portfolio, TWE, pp. 745, 749Assessment, TWE, pp. 747

Performance AssessmentAlternative Lab, TWE, p. 744MiniLabs, SE, pp. 746, 750BioLab, SE, pp. 754-755BioLab, TWE, pp. 754-755MiniLabs, TWE, pp. 746, 750

Knowledge AssessmentAssessments, TWE, pp. 744, 747Problem-Solving Labs, TWE, pp. 744, 749Section Assessments, SE, pp. 747, 753Chapter Assessment, SE, pp. 757-759

Skill AssessmentMiniLabs, TWE, pp. 746, 750Assessments, TWE, pp. 752, 753

Mollusks andSegmented Worms

What You’ll Learn■ You will distinguish among

the classes of mollusks andsegmented worms.

■ You will compare and con-trast the adaptations of mol-lusks and segmented worms.

Why It’s ImportantMollusks are an important food source for many animals,including humans. Some mollusks are filter feeders that clean impurities out oftheir watery environment.Earthworms turn, aerate, and fertilize the soil in whichthey live.

Observing a SnailGently hold a snail in yourhand. Describe the texture of the snail’s muscular foot.How does a snail move?

To find outmore about

mollusks and segmentedworms, visit the GlencoeScience Web Site. www.glencoe.com/sec/science

27

GETTING STARTEDGETTING STARTED

ChapterChapter

Mucus is an importantadaptation for earth-worms, as well as forslugs and snails. In addi-tion to allowing earth-worms to move throughsoil, mucus holds twoearthworms together asthey mate.

740

740

Theme DevelopmentThe theme of unity withindiversity is evident throughoutthe chapter. When comparingand contrasting these animalgroups, similarities are pointedout while the unique characteris-tics of classes and species areemphasized. The theme of evo-lution is stressed through discus-sions of the origins of mollusksand the increasing complexity ofthe specialization of the bodyplans of mollusks and segmentedworms.

Chapter 27Chapter 27

MultipleLearningStyles

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

Kinesthetic Portfolio, pp. 745,749; Meeting Individual Needs,

p. 751Visual-Spatial Quick Demo, p. 742; Display, p. 745; Reteach,

pp. 747, 753; Visual Learning, p. 752Intrapersonal Biology Journal,p. 742

Linguistic Biology Journal, p. 748Logical-Mathematical MeetingIndividual Needs, p. 746Naturalist Project, p. 746

GETTING STARTED DEMOGETTING STARTED DEMO

Display several seashells andhave students speculate aboutwhat kinds of animals mighthave lived in them. Explain thatthe animals that lived in theshells are classified as mollusks.P

LS

L1

P

LS

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

Resource ManagerResource Manager

Section Focus Transparency 67and Master

P

ELL

LS

L1

P

LS

ExcurrentSiphon

Incurrent Siphon

Mantle

27.1 MOLLUSKS 743

A Clam

C lams are bivalve mollusks. Bivalves includemussels, scallops, oysters, and other mollusks

with two hinged shells. Clams, like oysters, can covera foreign object, such as a grain of sand or a parasite,that has become lodged between its shell and its mantlewith layers of shell that eventually form a pearl.

Critical Thinking What function do gills have in digestion in a clam?

INSIDESSTORTORYY

INSIDE

11

22

77

Nephridia Tube-like structurescalled nephridiaform a clam’sexcretory system.

33

44

55

66

Mouth andStomach Foodparticles pass fromthe gills, wherethey have been fil-tered from thewater, to themouth, and thento the stomach,where digestionbegins.

88

Heart A bivalve has a three-chambered heart and an open circu-latory system. Its heart beats slowly,from 2 to 30 times per minute. Somemollusks, such as squids, have closedcirculatory systems.

Shell The body of abivalve is held betweentwo hinged shells.

Muscle The two shellsare drawn together bytwo muscles on oppo-site sides of the clam’sbody. The shells arekept closed when theanimal requires protec-tion. Bivalves can moveby rapidly opening andshutting their hingedshells.

Siphons In a clam, theedges of the mantle formtwo siphons that let waterin and out of the clam. Insome clams, the siphonscan be extended to thewater above the sandwhere the clam is buried.

Gills Gas exchange occursthrough the mantle and thegills. The gills also filter foodparticles from the water.

Foot A clam begins movement byextending a muscular foot frombetween its shells. When the foot isanchored in the mud or sand, themuscles in the foot shorten, therebypulling the animal forward.

Coquina clams

743

IINSIDENSIDESSTORTORYY

INSIDE

PurposeStudents study the functions ofthe organs of a bivalve mollusk.

Teaching Strategies■ Ask students to explain thefunctions of the clam’s incurrentand excurrent siphons.■ Explain that the clam movesby extending its foot from theopening between the two shells.

Visual Learning■ Have students examine the

captions and make a simpledrawing in their journals thatshows the path that food takesin a clam.

Critical ThinkingGills filter food particles from thewater.

Building a ModelFill a surgical glove with water.Squeeze the water in one of thefingers and have students observehow the water moves freely intothe other parts of the glove.Explain that the glove roughlymodels an open circulatory sys-tem in which blood moves freelyinto open spaces surroundingorgans.

P

LS

L1

P

LS

P

ELL

LS

L1

P

LS

L2

P

LS

P

LS

Head

Head

MantleMantle

Foot

Arm

Tentacle

ShellGut

Gut

Reduced Internal ShellSnail

Squid

Visceral mass

Mantle

Shell

Foot

Figure 27.3Look at the clam shell in this photo and locate a small hole onits edge. This tiny hole was made by the radula of a mollusk that ate the clam, leaving its shell behind to tell the tale of the clam’s fate.

Some mollusks have shells, andothers, including slugs and squids, areadapted to life without a hard cover-ing. All mollusks have bilateral sym-metry, a coelom, two body openings,a muscular foot for movement, and amantle. The mantle (MANT uhl) is athin membrane that surrounds theinternal organs of the mollusk. Inshelled mollusks, the mantle secretesthe shell.

Although mollusks look differentfrom one another on the outside,they share many internal similarities.You can see the similarities and thedifferences in these body areas inFigure 27.2 as you compare a snailand a squid. How does a clam buriedin sand obtain its food? Find out inthe Inside Story on the next page.

How mollusks obtain foodHave you ever watched a snail clean

algae from the sides of an aquarium?Snails, like many mollusks, use a rasp-ing structure called a radula to obtainfood. A radula (RAJ uh luh), locatedwithin the mouth of a mollusk, is atonguelike organ with rows of teeth.The radula is used to drill, scrape,grate, or cut food. Figure 27.3 showsthe results of the use of a radula.Octopuses and squids use their radu-las to pull food they have capturedinto their mouths. Other mollusksare grazers, some are predators, andsome are filter feeders. Bivalves donot have radulas; they obtain food byfiltering it out of the water.

Reproduction in mollusksMost mollusks have separate sexes

and reproduce sexually. Eggs andsperm are released at the same timeinto the surrounding water, whereexternal fertilization takes place.Many gastropods that live on landare hermaphrodites. The ability to produce both eggs and sperm is anadaptation commonly found in slow-moving animals because it increasesthe likelihood of fertilization.

742 MOLLUSKS AND SEGMENTED WORMS

Figure 27.2A mollusk has a soft body composed of a foot,a mantle, and a visceralmass that contains internal organs. Somemollusks also have ashell. Compare the structures of a snail and a squid.

Snails have a well-definedand developed head area inaddition to a large foot.

AA The foot area of the squid appears tohave been modified into arms andtentacles that are used for capturingand holding prey.

BB

742

2 Teach

Quick DemoQuick Demo

Visual-Spatial Divide theclass into groups. Give

each group a live land snail onone half of a petri dish. Ask students to record theirobservations of the snail.Instruct students to observe thesnail through the underside ofthe dish. Have them gentlytouch the antenna of the snailwith the eraser end of a penciland observe and describe itsreaction. Finally, have themplace the snail on a piece of let-tuce to see if they can observethe snail feeding. Discuss allobservations as a class.

P

COOP LEARN

LS

P

LSP

ELL

LS

L2

P

LS

Quick DemoQuick Demo

Obtain a whole squid from afish market. Point out the headand tentacles of the squid. Cutthe squid open to reveal itstransparent cuttlebone. Explainthat many scientists considerthe cuttlebone to be a remnantof a shell.

P

LS

L1

P

LS

BIOLOGY JOURNAL BIOLOGY JOURNAL

Locating Mollusks Intrapersonal Provide students with ablank outline map of the world. Have

them conduct research to find out where fivespecies of mollusks are commonly found. Forexample, the Atlantic bay scallop is com-monly found from North Carolina to the WestIndies and Brazil. Ask students to develop a

key to indicate these locations on their maps.Have them locate both freshwater and salt-water species. Encourage students to com-bine their findings with those of two othersin the class. If possible, provide students withnature and wildlife atlases to aid in theirresearch.

P

LSP

ELL

LS

L3

P

LS

Cultural DiversityPearl Cultivation In your lessons on mollusk biology, discusswith students how pearls are formed anddescribe the pearl cultivation industry inJapan. Since 1893, pearl farming has beenone of Japan’s most famous industries.

To add interest, introduce students to theAMA women of Japan. The AMA is a groupof diving women who collect pearls and

valuable mollusks from the ocean. Divingwomen have operated in Japan for morethan 2000 years. The divers take their namefrom the word ama, which in the ancientJapanese language meant “ocean” or “sky.”The AMA of Japan have been known to diveto depths greater than 50 meters hundredsof times daily without the use of snorkels orair tanks.

CD-ROMBiology: The Dynamicsof Life

Exploration: MollusksDisc 4

VIDEODISCThe Secret of LifeMolluscan Body Plan

!7;E~I"

VIDEODISCBiology: The Dynamicsof Life

Scallop Escape (Ch. 32)Disc 1, Side 2, 11 sec.

!:@É"

Respiration in mollusksMost mollusks have respiratory

structures called gills. Gills are spe-cialized parts of the mantle that con-sist of a system of filamentous projec-tions that contain a rich supply of blood for the transport of gases.Gills increase the surface areathrough which gases can diffuse. Inland snails and slugs, the mantle cav-ity appears to have evolved into aprimitive lung.

Excretion in mollusksMollusks are the oldest known ani-

mals to have evolved excretory struc-tures called nephridia. Nephridia(nih FRIHD ee uh) are organs thatremove metabolic wastes from ananimal’s body. Mollusks have one ortwo nephridia that collect wastesfrom the coelom. Wastes are dis-charged into the mantle cavity, andexpelled from the body by the pump-ing of the gills.

Diversity of MollusksWithin the large phylum of mol-

lusks, there are seven classes. Thethree classes that include the mostcommon and well-known species are Gastropoda, Bivalvia, andCephalopoda.

Gastropods: One-shelled mollusksThe largest class of mollusks is

Gastropoda, or the stomach-footedmollusks. The name comes from theway the animal’s large foot is posi-tioned under the rest of its body.Most species of gastropods have asingle shell. Other gastropod species,such as slugs, have no shell.

Shelled gastropods include snails,abalones, conches, periwinkles,whelks, limpets, cowries, and cones.They can be found in freshwater,saltwater, or moist terrestrial habi-tats. Shelled gastropods may be planteaters, predators, or parasites. Figure 27.5 shows two examples ofshelled gastropods.

Instead of being protected by ashell, the body of a slug is protectedby a thick layer of mucus. Colorfulsea slugs, also called nudibranchs,are protected in another way. Whencertain species of sea slugs feed on jellyfishes, they incorporate thepoisonous nematocysts of the jelly-fish into their own tissues withoutcausing these cells to discharge. Anyfishes trying to eat the sea slugs arerepelled when the nematocysts discharge into the unlucky predator.The bright colors of these gastropodswarn predators of the potential dan-ger, as shown in Figure 27.6.

27.1 MOLLUSKS 745

Figure 27.5Shelled gastropodsvary from petite,thin-shelled speciesto large animalswith thick shells.

Figure 27.6Sea slugs such as thisChromodoris specieslive in the ocean.They eat hydras, seaanemones, and seasquirts.

The pinkconch is a large gastropodwith a thickshell.

AA

The smooth doveshell is a small, deli-cate gastropod. Theseorganisms can befound in the Florida

Keys and WestIndies.

BB

Visual LearningAsk students to examine the pho-tos of the conch and dove shelland speculate about why peoplewant shells as souvenirs. Askthem how the practice of collect-ing rare live mollusks for the saleof their shells might be curtailed.

DisplayVisual-Spatial Have studentsbring in gastropod shells

from collections they have athome. Make a display of theshells. Provide shell identificationkeys and books and have studentstry to identify the shells and tellwhich are plant eaters, predators,and parasites.

P

ELL

LS

L2

P

LS

sandpaper that has been marked in itscenter with an X. Measure the distancethe snail travels in 3 minutes.

6. Place the lamp on a ring stand about30 cm from the snail. After 3 minutes,begin timing. Measure the distancethe snail travels in 3 minutes.

7. Place your container with the snail ontop of another tray containing crushedice. After 5 minutes, measure the dis-tance the snail travels in 3 minutes.

Expected ResultsSnails will move fastest on a smooth sur-face in warm conditions.Analysis

1. Was your hypothesis supported by thedata? Yes, if they hypothesized thatthe snail would move fastest whenwarm, in light, and on a smooth sur-face.

2. What feature of snails aids their glid-ing movement? mucus

Performance Have studentsdesign and conduct an experiment thatwould test to see if land snails preferlight or darkness. Use the PerformanceTask Assessment List for Designing anExperiment in PASC, p. 23. L1

P

LS

AssessmentAssessment

745

Find out more about reproductionin mollusks by reading the Problem-Solving Lab on this page.

Although members of the phylumMollusca have different appearancesas adults, they all share similar devel-opmental patterns. The larval stagesof all mollusks are similar, as you cansee in Figure 27.4.

Some marine mollusks have free-swimming larvae that propel them-selves by cilia. In addition to larvae,most marine snails and bivalves haveanother developmental stage called aveliger in which the beginnings of afoot, shell, and mantle can be seen.

Nervous control in mollusksMollusks have simple nervous sys-

tems that include a brain and associ-ated nerves that coordinate theirmovement and behavior. Most mol-lusks have paired eyes that rangefrom simple cups that detect light tothe complex eyes of octopuses thathave irises, pupils, and retinas thatfunction as well as those of humans.

Circulation in mollusksMollusks have a well-developed

circulatory system that includes athree-chambered heart. In most mollusks, the heart pumps bloodthrough an open circulatory system.In an open circulatory system, theblood moves through vessels and into open spaces around the bodyorgans. This adaptation exposes bodyorgans directly to blood that containsnutrients and oxygen, and removesmetabolic wastes. Some mollusks, suchas octopuses, move nutrients and oxy-gen through a closed circulatory sys-tem. In a closed circulatory system,blood moves through the bodyenclosed entirely in a series of bloodvessels. A closed system provides anefficient means of gas exchangewithin the body.

744 MOLLUSKS AND SEGMENTED WORMS

How do freshwater clams reproduce?

AnalysisExamine the life cycle of the freshwater clam Anodonta.

Freshwater clams are either male or female. Immature larvae,called glochidia, are formed within female clams’ reproduc-tive systems, then released in the surrounding water.

Thinking Critically1. What cell type must enter a female clam’s body in order

for glochidia to form? 2. What reproductive process must occur prior to the forma-

tion of glochidia? 3. Glochidia attach to and feed off of a specific fish host.

Predict what happens to glochidia if no host is available.4. How do glochidia change while attached to their host?5. It is estimated that a single clam can release over

1 000 000 glochidia. How might this be an adaptation to a life cycle that includes a parasitic stage?

Problem-Solving Lab 27-1 Observing andInferringProblem-Solving Lab 27-1

Juvenileclam falls off

HookGLOCHIDIUM

Glochidia becomeattached to finsand gill filaments

Muscle

0.02mm

Glochidiaexpelled byadult clam

Adultclam Juvenile

clam

Shell

Foot

Figure 27.4Larvae of most mollusksresemble a spinning topwith tufts of cilia. Mostof these larvae are freeswimming before settlingto the ocean floor foradult life. Mollusk larvaeare an important part ofmany food chains.

PurposeStudents will study the life cycleof larval development in a fresh-water mussel.

Process Skillsthink critically, analyze data,interpret scientific drawings

Teaching Strategies■ Remind students that all mol-lusks do not follow the pattern ofreproduction and developmentillustrated here.

Thinking Critically

1. sperm2. fertilization3. They die.4. They mature into adult mus-

sels.5. Although the animal pro-

duces many glochidia, mostdo not find a suitable hostand thus do not survive toadult stage.

Knowledge Provide stu-dents with a sample of glochidiabut do not tell them what they are looking at. Have them examineglochidia under the microscopeand identify what the organism is.Preserved glochidia are availablefrom biological supply houses.Use the Performance Task As-sessment List for Making Obser-vations and Inferences in PASC,p. 17.

P

ELL

LS

L2

P

LS

AssessmentAssessment

P

LS

Alternative LabComparing Snail Speeds

PurposeStudents will compare the speed at whichsnails move under various environmentalconditions.Materialsland snails, clear plastic deli trays or large

P

LS

deli containers, wax marking pencil, lampwith 60-watt bulb, crushed ice, ring stand,black construction paper, sandpaper, metricrulerProcedureGive students the following directions.

1. Make a table for distances traveled bythe snail on a smooth surface, a roughsurface, in cold conditions, and in warmconditions.

2. Make a hypothesis about the conditions

under which the snail will move thefastest.

3. With the wax marking pencil, mark anX in the middle of your tray. Place thesnail on this X and measure how far ittravels in 3 minutes.

4. Place a piece of black constructionpaper over the tray so that the snail isin the dark. Measure distance traveledin 3 minutes.

5. Cover the bottom of the tray with744

Problem-Solving Lab 27-1Problem-Solving Lab 27-1

PortfolioPortfolio

Observing FilterFeeding

Kinesthetic Have stu-dents place a live clam

in a beaker of water so that 6 cm of water covers the clam.Place 2 drops of carmine pow-der suspension near the siph-ons. Ask students to explainwhat happens to the carminesuspension, and have themplace their explanations intheir portfolios.P

LS

PP

LSP

ELL

LS

L2

P

LS

Cephalopods: Head-footed mollusks

The head-footed mollusks are in the class Cephalopoda. Allcephalopods are marine organisms.This class includes the octopus, squid,cuttlefish, and chambered nautilus, asshown in Figure 27.8. The onlycephalopod with a shell is the cham-bered nautilus, but some species,such as the cuttlefish, have a reducedinternal shell. Scientists consider thecephalopods to have the most com-plex structures and to be the mostrecently evolved of all mollusks.

In cephalopods, the foot has evolvedinto tentacles with suckers, hooks, oradhesive structures. Cephalopodsswim or walk over the ocean floor in

27.1 MOLLUSKS 747

Section AssessmentSection Assessment

Understanding Main Ideas1. Describe how mucus is important to some

mollusks.2. What adaptations make cephalopods effective

predators?3. Compare filter feeding with obtaining food

by using a radula.4. Compare how squids and sea slugs protect

themselves.

Thinking Critically5. How are the methods of movement for the snail,

clam, and squid related to the structure of eachone’s foot?

6. Classifying Construct a key to identify thethree classes of mollusks discussed. For morehelp, refer to Organizing Information in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

pursuit of their prey, capturing itwith their tentacles. Once tentacleshave captured prey, it is brought tothe mouth and bitten with thebeaklike jaws. Then the food ispulled into the mouth by the radula.

Like bivalves, cephalopods havesiphons that expel water. These mol-lusks can expel water forcefully inany direction, and move quickly byjet propulsion. Squids can attainspeeds of 20 m per second using thissystem of movement. You may beaware that cephalopods use jetpropulsion to escape from danger.They also can release a dark fluid tocloud the water. This "ink" helps toconfuse their predators so they canmake a quick escape.

b

a

c

Figure 27.8The class cephalopoda includessquids (a) and octopuses (b). The genus Nautilus is the onlyremaining living example ofa cephalopod with an externalshell (c). All other members ofthis class are extinct.

Knowledge Ask studentsto do library or Internet researchto find out why octopuses are themost intelligent invertebrates.Ask how a nervous system sup-ports the level of intelligenceshown by octopuses.

3 AssessCheck for UnderstandingHave students explain how mol-lusks are more complex thanother animals they have studied.

ReteachVisual-Spatial Have studentsmake a table describing mol-

lusk traits with these headings:Phylum, Representative Organ-isms, Symmetry, Habitat, FoodGetting, Taking in Oxygen, Re-production, and Protection.

ExtensionAsk students to prepareillustrated reports on pearl

cultivation.

Portfolio Ask students towrite a description of a habitatthat is suited to a specific molluskfrom each group. Have studentsexplain how each organism isadapted to its habitat.

4 CloseDiscussionDiscuss the economic importanceof mollusks. Include uses of mol-lusks as food, algae feeders inaquariums, and as souvenirs.

P

LS

L2

P

LS

AssessmentAssessment

L1

P

LS

L2

P

LS

P

LS

L2

P

LS

AssessmentAssessmentBivalves: Two-shelled mollusksTwo-shelled mollusks such as

clams, oysters, and scallops belong tothe class Bivalvia, illustrated inFigure 27.7. Most bivalves aremarine, but a few species live infreshwater habitats. Bivalves occur ina range of sizes. Some are less than 1mm in length and others, such as thetropical giant clam, may be 1.5 mlong. Bivalves have no distinct heador radula. Most use their large, mus-cular foot for burrowing in the mudor sand at the bottom of the ocean ora lake. A ligament, like a hinge, con-nects their shells; strong musclesallow the shell to open and close overthe soft body. See if you can identifythe shells pictured in the MiniLab byusing the dichotomous key given.

One of the main differencesbetween gastropods and bivalves isthat bivalves are filter feeders thatobtain food by filtering small parti-cles from the surrounding water.Bivalve mollusks have several adapta-tions for filter feeding, including cilia that beat to draw water inthrough an incurrent siphon. Aswater moves over the gills, food andsediments become trapped in mucus.Cilia that line the gills push food par-ticles to the stomach. Cilia also act asa sorting device. Large particles, sed-iment, and anything else that isrejected is transported to the mantlewhere it is expelled through theexcurrent siphon, or to the foot,where it is eliminated from the ani-mal’s body.

746 MOLLUSKS AND SEGMENTED WORMS

Identifying Mollusks Have you ever taken a walk on thebeach and filled your pockets with shells, and as you exam-ined them later, wondered what they were? Use the follow-ing dichotomous key to determine the names of the shells.

Procedure! To use a dichotomous key, begin with a choice from the

first pair of descriptions.@ Follow the instructions for the next choice. Notice that

either a scientific name can be found at the end of eachdescription, or directions will tell you to go on to anothernumbered set of choices.1A One shell ...............................................Gastropods see 21B Two shells....................................................Bivalves see 32A Flat coil.................. Sundial shell: Architectonica nobilis2B Thick coil ...................................................................see 43A Shelf inside shell ....................Common Atlantic slipper:

Crepidula fornicata3B No shelf inside shell..................................................see 54A Spotted surface...........Junonia shell: Scaphella junonia4B Lined surface ...Banded tulip shell: Fasciolaria hunteria5A Polished surface ...Sunray shell: Macrocallista mimbosa5B Rough surface.....Lion’s paw shell: Lyropecten nodosus

Analysis1. Why is a dichotomous key used for a variety of organisms?2. What shell features were easy to pick out using the key?

What features were more difficult?3. What general feature was used to identify shells?

MiniLab 27-1MiniLab 27-1 Comparing and Contrasting

Figure 27.7In bivalves the mantleforms two siphons,one for incomingwater and one forwater that is excreted.

a b

d

f

e

c

PurposeStudents will use a dichotomouskey to identify mollusks based ontheir shells.

Process Skillsobserve and infer, compare andcontrast, classify, use a dichoto-mous key

Teaching Strategies■ Make an overhead transparencyof a dichotomous key. Use thetransparency to demonstrate howa dichotomous key is used.■ Ask students who collect shellsto bring in their shell collectionsand identify the shells for theirclassmates.

Expected ResultsStudents will classify the picturedshells using the dichotomous keyprovided.

Analysis1. A dichotomous key divides a

group into smaller and small-er groups until each organismis identified.

2. easy: 1, 2, 3, 4; more difficult,5, because it requires moreinterpretation and closer com-parison

3. one or two shells

Skill Give students a simpledichotomous key for several shells.Ask them to use the key to identifythe shells. Use the PerformanceTask Assessment List for Makingand Using a Classification Systemin PASC,p. 49. L1

P

LS

AssessmentAssessment

P

LS

MiniLab 27-1MiniLab 27-1

MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

Gifted Logical-Mathematical Ask studentsto design an experiment to compare

the strength of muscles in bivalves such asclams and scallops. Remind them to planto collect quantitative data.

P

LS

L3

P

LS

P R O J E C TClassifying Mollusks Used asFood

Naturalist Have students photo-copy a menu from a local seafood

restaurant. Ask students to construct a keyto identify the gastropods, bivalves, andcephalopods listed on the menu. Have stu-dents summarize the importance of mol-lusks as a food source.

P

LSP

ELL

LS

L2

P

LS

Resource ManagerResource Manager

Reteaching Skills Transpar-ency 40 and Master

Biolab and MiniLab Work-sheets, p. 121

Reinforcement and StudyGuide, pp. 119-121

Content Mastery, p. 134Laboratory Manual,

pp. 191-198 L2

P

LS

L1

P

LS

L2

P

LS

L2

P

LS

P

ELL

LS

L1

P

LS

746

Section AssessmentSection AssessmentSection Assessment1. Mucus enables mollusks to stick to sur-

faces and slide easily through or onmaterials in their habitats. Some mol-lusk mucus contains poisons.

2. jet propulsion-type swimming, tenta-cles with suckers, large eyes with awell-developed nervous system, radulafor tearing apart prey

3. A filter feeder takes in water and fil-

ters out food. The radula is a tongue-like organ that scrapes food from sur-faces.

4. Squids protect themselves by their abil-ity to move quickly away from danger.Sea slugs are protected by their toxicmucous covering.

5. The muscular foot of the snail secretesmucus on which the snail glides slowly.

The clam can burrow into sand with itsmuscular foot. The squid’s foot is mod-ified into tentacles that help obtainfood.

6. Students’ keys should include informa-tion found in the chapter under head-ings dealing with gastropods, bivalves,and cephalopods.

747

each segment can move the animalalong.

Segmented worms can be found inmost environments, except in thefrozen soil of the polar regions andthe dry sand and soil of the deserts.You may be familiar with the earth-worms in your garden, but these arejust one of about 12 000 species ofsegmented worms that live in soil,freshwater, and the sea. Can youidentify a segmented worm? Find outby reading the Problem-Solving Labon this page.

Segmentation supports diversified functions

The most distinguishing charac-teristic of segmented worms is theircylindrical bodies that are dividedinto a series of ringed segments, asseen in the worms in Figure 27.10.This segmentation continues inter-nally as each segment is separatedfrom the others by a body partition.Segmentation is an important adap-tation for movement because eachsegment has its own muscles, allow-ing shortening and lengthening ofthe body.

If you examine each segment ofmost annelids, you find that the bodyis made up of identical segments.Segmentation, however, also allows forspecialization of body tissues. Groupsof segments may be adapted for aparticular function. Certain segmentshave modifications for functions suchas sensing and reproduction.

Nervous system in segmented worms

Segmented worms have simple ner-vous systems in which organs in ante-rior segments have become modifiedfor sensing the environment. Somesensory organs are sensitive to light,and eyes with lenses and retinas haveevolved in certain species. In some

species there is a brain located in ananterior segment. Nerve cords con-nect the brain to nerve centers calledganglia, located in each segment. Youcan find out how earthwormsrespond to their environment in theBioLab at the end of this chapter.

When is it an annelid? You are on a zoological researchexpedition to South America. As the invertebrate specialist, youare asked by your fellow scientists to classify a number of animals.

Analysis

Thinking CriticallyWhich are annelids, which are not, and which require

more study to decide? Explain your answer for each animal.

Problem-Solving Lab 27-2Problem-Solving Lab 27-2 Classifying

Figure 27.10Segmentation is easilyseen in earthworms (a).The giant earthworm ofAustralia can be morethan 3 m long (b).

Animal

A

B

C

D

E

F

Characteristics

externally segmented body, no internal segments

no coelom, but has internal segments

lives in water, has two body openings, sexes are separate

backbone present, has digestive, circulatory, excretory systems

both male and female reproductive organs present

externally segmented body, has internal segments

Data Table

a

b

2 Teach

PurposeStudents will have to judge if cer-tain traits are or are not associ-ated with the phylum Annelida.

Process Skillsapply concepts, think critically,compare and contrast, draw aconclusion

Teaching Strategies■ Be sure that students have readthe entire section on annelidsbefore attempting to do this lab.■ Review any terms that may notbe familiar to students.■ Review the concept of a bodycavity called a coelom.

Thinking CriticallyA— no, all annelids have internal

segmentationB— no, all annelids have a

coelomC— undecided; traits may apply

to other phyla as well asAnnelida

D—no, annelids are not verte-brates

E— undecided; traits may applyto other phyla as well asannelids

F— yes, true only of annelids

Knowledge Ask studentsto list traits that are specific toAnnelida and no other phyla. Askstudents to list traits that arecommon to other phyla as well asAnnelida. Use the PerformanceTask Assessment List for Makingand Using a Classification Systemin PASC, p. 49. L2

P

LS

AssessmentAssessment

P

LS

Problem-Solving Lab 27-2Problem-Solving Lab 27-2

Section

What Is a SegmentedWorm?

Segmented worms are classified inthe phylum Annelida. They includethe earthworms, leeches, and bristle-worms, shown in Figure 27.9.Segmented worms are bilaterallysymmetrical and have a coelom andtwo body openings. Some have a lar-val stage that is similar to the larvalstages of certain mollusks, suggestinga common ancestor.

The basic body plan of segmentedworms is a tube within a tube. Theinternal tube, suspended within thecoelom, is the digestive tract. Food istaken in by the mouth, an opening inthe anterior end of the worm, andwastes are released through the anus,an opening at the posterior end.

Most segmented worms have tinybristles called setae (SEE tee) on eachsegment. The setae help segmentedworms move by providing a way toanchor their bodies in the soil so

Do earthworms have a front anda back end? Yes, they do. In fact,if you have ever watched one

move, you know that it crawls by firststretching the front of its body forward,and then pulling the back of its body up to thefront. A worm in motion looks a little like anaccordion playing.

SECTION PREVIEW

ObjectivesDescribe the character-istics of segmentedworms and their impor-tance to the survival of these organisms.Compare and contrastthe classes of segmentedworms.

Vocabularysetaegizzard

27.2 Segmented Worms

Figure 27.9The phylum Annelidacontains about 12 000species, which areplaced in three classes.

OriginWORDWORD

annelidFrom the Latinword anellus, mean-ing “tiny ring.” The bodies ofannelids, the seg-mented worms, looklike stacks of tinyrings.

Earthworms have only afew setae on each seg-ment. An earthworm doesnot have a distinct head.

AA

748

Leeches live in marine, freshwater, or terres-trial habitats. All leeches have 32 segments.

BB

Bristleworms havedistinct heads, eyes,and tentacles. Theyare mostly marineanimals.

CC

Earthworm

748

Section 27.2

PrepareKey ConceptsStudents will learn the character-istics of segmented worms thatenable them to survive in theirenvironments. The classes of seg-mented worms will be comparedand the traits of animals that aremore complex than those studiedin previous chapters will beemphasized.

Planning■ Set up an earthworm farm for

the Quick Demo.■ Gather large jars and large

earthworms for the Portfolio.■ Gather live earthworms, glass

pans, sandpaper, penlights,culture dishes, droppers, ice,warm tap water, thermome-ters, and hand lenses or stereo-microscopes for the BioLab.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 68 on the overhead pro-jector and have students answerthe accompanying questions.

P

ELL

LS

L1

P

LS

BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Use with Chapter 27,Section 27.2

How does the body of the earthworm differ from thatof the roundworm?

How might this difference be an advantage?

11

22

Transparency Segmented Worms68 SECTION FOCUS

Cop

yrig

ht ©

Gle

ncoe

/McG

raw

-Hill

, a d

ivis

ion

of T

he M

cGra

w-H

ill C

ompa

nies

, Inc

.

Earthworm Roundworm

BIOLOGY JOURNAL BIOLOGY JOURNAL

Earthworm Importance Linguistic Ask a group of students to interview a farmer

or an agriculture professor about theimportance of earthworms in agriculture.Have them present their findings to theclass in an illustrated report. Ask otherclass members to take notes on the pre-sentation.

P

LS

L2

P

LS

Earthworm Terrariums Kinesthetic Ask each group of studentsto prepare a large jar as a terrarium for

earthworms. Have them place rocks on thebottom for drainage. Then, have studentsalternate layers of moist sand and topsoil ontop of the rocks. Have them add about six toeight worms to the jar, then cover the top

layer of soil with dead leaves and grass.Instruct students to tape black paper to theoutside of the jar. After several days, havethem remove the paper and observe whathappened to the leaves, grass, and soil lay-ers. Have them also describe any tunnelsthey observe.

P

COOP LEARN

LS

P

LS

PP

LSP

ELL

LS

L1

P

LS

PortfolioPortfolio

VIDEODISCThe Secret of Life Earthworm

!7;F$A"749

Resource ManagerResource Manager

Section Focus Transparency 68and Master

P

ELL

LS

L1

P

LS

751

An Earthworm

As an earthworm burrows through soil, it loosens, aerates, and fertilizes the soil. Burrows provide passage-

ways for plant roots and improve drainage of the soil.

Critical Thinking In what way is segmentation an importantadvantage in earthworm movement?

Earthworm

INSIDESSTORTORYY

INSIDE

Mouth An earth-worm takes soilinto its mouth, thebeginning of thedigestive tract.

11

Crop The crop is asac that holds soiltemporarily beforeit is passed into the gizzard.

22

Setae An earthwormalternately contracts setsof longitudinal and circu-lar muscles to move. Firstit contracts its longitudi-nal muscles on severalsegments, which bunchup. This causes tiny setaeto protrude, anchoringthe worm in the soil. Thenthe earthworm’s circularmuscles contract, thesetae are withdrawn, andthe worm moves forward.

77

Nephridia Nephridia areexcretory structures that elimi-nate metabolic wastes fromeach segment.

66

Gizzard The gizzardgrinds the organic mat-ter, or food, into smallpieces so that the nutri-ents in the food can beabsorbed as it passesthrough the intestine.Undigested food andany remaining soil areeliminated through theanus.

33

Circulatory system The closedcirculatory system consists ofenlarged blood vessels that areheavily muscled. When thesemuscles contract, they help pumpblood through the system, muchas a heart does in other animals.

44

Nervous system Anearthworm has a systemof nerve fibers in eachsegment. The nerve fibersare coordinated by a sim-ple brain that lies abovethe mouth. An earth-worm also has a ventralnerve cord.

55

751

IINSIDENSIDESSTORTORYY

INSIDE

PurposeStudents will examine the inter-nal structures of the earthwormand their functions.

Teaching Strategies■ Ask students to write a paragraph that explains howearthworm bodies show morecomplexity than the bodies offlatworms and roundworms.■ Obtain a plastic model of anearthworm. Point out each struc-ture discussed in the Inside Storyon the model.■ Challenge your advanced stu-dents to make a table that com-pares earthworms with the free-living flatworms and roundworms.Students should include the fol-lowing in their tables: digestion,locomotion, circulation, excretion,and sensory functions.

Visual Learning■ Make photocopies of the In-

side Story diagram without thelabels and captions. Have stu-dents label and describe thefunctions of each structure onthe photocopy as it is dis-cussed.

Critical ThinkingEarthworms have setae and mus-cles in each segment. They moveby anchoring the setae in theground, then contracting theirmuscles. The earthworm movesby alternately contracting andrelaxing the muscles in each seg-ment.

P

ELL

LS

L1

P

LS

L3

P

LS

L2

P

LS

P

LS

Circulation and respiration Segmented worms have a closed

circulatory system. Blood carryingoxygen to and carbon dioxide frombody cells flows through vessels toreach all parts of the body.Segmented worms must live in wateror in wet areas on land because theyalso exchange gases directly throughtheir moist skin.

Digestion and excretionSegmented worms have a complete

internal digestive tract that runs thelength of the body. Food taken in bythe mouth passes to the gizzard, a sacwith muscular walls and hard parti-cles that grind soil before the soilpasses into the intestine. Undigestedmaterial and solid wastes pass out the

worm’s body through the anus.Segmented worms also have twonephridia in each segment that col-lect waste products and transportthem through the coelom and out ofthe body. Find out what an earth-worm eats by reading the Inside Story.

Reproduction in segmented wormsMost segmented worms are her-

maphrodites. During mating, twoworms exchange sperm. Each wormforms a capsule for the eggs andsperm. The eggs are fertilized in eachworm’s capsule, then the capsule slipsoff the worm and is left behind in thesoil. In two to three weeks, youngworms emerge from the eggs.Earthworms and leeches both repro-duce in this way.

However, bristleworms and theirrelatives have separate sexes andreproduce sexually, although matingoccurs in only a few species. Usuallyeggs and sperm are released into theseawater, where fertilization takesplace. Young bristleworms hatch inthe sea.

Diversity of Segmented Worms

The phylum Annelida is dividedinto three classes: class Oligochaeta,earthworms; class Polychaeta, bristle-worms and their relatives; and classHirudinea, leeches.

Earthworms Earthworms are the most well-

known annelids because they can beseen easily by most people. Althoughearthworms have a definite anteriorand posterior section, they do nothave a distinct head. Earthwormshave only a few setae on each seg-ment. What does an earthworm looklike internally? You can find out inthe MiniLab on this page.

750 MOLLUSKS AND SEGMENTED WORMS

A Different View of an Earthworm What does an earthworm look like internally? You could look at it many different ways—from the dorsal or ventral side, along the length of the animal (a longitudinal view), or in cross section through a segment.

Procedure! Diagram A illustrates a

longitudinal dorsal view of the internal organs of an earthworm. Note that the segments are numbered.

@ Use Diagram B as a guide to how a cross- section slice appears through segment 9.

AnalysisMake your own cross-section diagrams of segments 8

and 12. Label all the parts shown in your diagrams.

MiniLab 27-2MiniLab 27-2 Interpreting Scientific Diagrams

Brain34

56789

10111213141516

12

Pharynx

Esophagus

Bloodvessel

Crop

Nephridia

AA

Blood vessel

Esophagus

Muscle layers

Nephridia

Ventral nervecord

BB

750

Purpose Students will use a diagram of anearthworm’s internal anatomy todraw cross-section views.

Process Skillsanalyze data, interpret scientificdrawings, observe and infer

Teaching Strategies■ Review the meaning of across-section view. Use a cucum-ber to show a longitudinal view.Then make cuts through thecucumber to illustrate cross-sec-tional slices.■ Point out to students that thesegments are numbered.■ Make copies of an outline dia-gram of incomplete worm cross-sectional views for student use.

Expected ResultsStudent diagrams will reflecttheir ability to translate informa-tion from a longitudinal view to across-sectional view.

AnalysisSegment 8 will show: muscles,esophagus, heart, dorsal and ven-tral blood vessels, and nerve cord.Segment 12 will show all the partsfrom Segment 8 plus the seminalvesicle and calciferous gland.

Skill Have students makecross-section diagrams of seg-ments 3, 16, and 21. Use thePerformance Task AssessmentList for Scientific Drawing inPASC, p. 55.

P

ELL

LS

L2

P

LS

AssessmentAssessment

P

LS

MiniLab 27-2MiniLab 27-2

MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

Visually Impaired/LearningDisabled

Kinesthetic For students who are visu-ally impaired, provide an earthworm

for them to hold while you point out themain features of its structure and behavior.Ask the students to explain how the earth-worm’s shape and texture make it adaptedfor life in the soil.

P

LSP

ELL

LS

L1

P

LS

Internet Address Book

Note Internet addressesthat you find useful in

the space below for quick reference.

VIDEODISCThe Infinite Voyage: To the Edge of the Earth

Exploring the Galapagos Islands (Ch. 4) 8 min.

!7KVF"

VIDEODISCThe Secret of LifeEarthworm Segment

!7;F.B"

Resource ManagerResource Manager

BioLab and MiniLab Work-sheets, p. 122 L2

P

LS

Resource ManagerResource Manager

Critical Thinking/ProblemSolving, p. 27

Concept Mapping, p. 27

P

ELL

LS

L1

P

LS

L3

P

LS

Section AssessmentSection Assessment

Understanding Main Ideas1. What is the most distinguishing characteristic of

members of the phylum Annelida? Why is itimportant?

2. Describe how bristleworms reproduce.3. How do earthworms improve soil fertility?4. Why are leeches classified in phylum Annelida?

Thinking Critically5. Polychaetes actively swim, burrow, and crawl.

How do parapodia support the active life that most polychaetes pursue?

6. Interpreting Scientific IllustrationsUsing the Inside Story, interpret how the two types of muscles in the earthworm are used to move the animal through the soil. For more help, refer to Thinking Critically in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

Origins of Mollusks andSegmented Worms

Fossil records show that molluskslived in great numbers as long as 500million years ago. Gastropod,bivalve, and cephalopod fossils havebeen found in early Paleozoicdeposits. Some species, such as thechambered nautilus, appear to havechanged very little from relatedspecies that lived long ago. Find outhow fossil mollusks are used to date

rocks in the Earth Science Connectionat the end of this chapter.

Annelids probably evolved in thesea, perhaps from larvae of ancestralflatworms. The fossil record for seg-mented worms is limited becausesegmented worms have almost nohard body parts. Tubes constructedby polychaetes are the most commonfossils of this phylum. Some of thesetubes appear in the fossil record asearly as 620 million years ago, as youcan see in Figure 27.12.

27.2 SEGMENTED WORMS 753

PRESENTCENOZOICPALEOZOICPRECAMBRIAN MESOZOIC

Bivalves10 000 species

Gastropods80 000 species

Annelids12 000 species

Nematodes12 000 species

Cestodes3500 species

Trematodes8000 species

Turbellarians3000 species

Cephalopods600 species

Figure 27.12Mollusks and segmentedworms are closely related.

ANIMALS

3 AssessCheck for UnderstandingShow students cross-sectionslides of planarians, earthworms,nematodes, tapeworms, andleeches. Ask them to distinguishthe segmented worms from theother worms. Have them explaintheir choices.

ReteachVisual-Spatial Ask studentsto draw a large diagram that

shows an earthworm’s nervous,circulatory, muscular, digestive,and execretory systems. Havethem label each structure andidentify the system or systems towhich it belongs.

ExtensionAsk students to interview a micro-surgeon who uses leeches toincrease the flow of blood to reat-tached body parts such as ears, fin-gers, and toes. Have them writeabout their interview as if it weregoing to appear in a magazine.They should ask the microsurgeonfor information about the chemi-cals in leech saliva that dilate bloodvessels to increase blood flow.

Skill Have students createa table that compares the charac-teristics of the three classes ofannelids.

4 CloseDiscussionDiscuss with students the charac-teristics that make annelids moreevolutionarily advanced than flat-worms or mollusks.

L1

P

LS

AssessmentAssessment

L3

P

LS

P

ELL

LS

L2

P

LS

L2

P

LS

Section AssessmentSection AssessmentSection Assessment1. segmentation; each segment has its own

muscles that lengthen and shorten forefficient movement; groups of segmentsmay take on specific functions

2. Bristleworms and their relatives have sep-arate sexes and reproduce sexually. Eggsand sperm are released into the water,where fertilization takes place.

3. As the earthworm burrows through the

soil, it loosens, aerates, and fertilizes thesoil.

4. Leeches have segmented bodies just likeother annelids.

5. Parapodia can be used for swimming orcrawling and in gas exchange.

6. Circular muscles contract to move theworm forward. Longitudinal muscles con-tract to pull the worm’s body along.

Earthworms eat their way throughsoil. As they eat, they turn the soiland provide spaces for air to flowthrough soil. As soil passes throughthe organs of their digestive tract,nutrients are extracted from food andundigested materials pass out of the

worm. The wastes of an earthwormare called castings. Castings help fer-tilize soil.

Bristleworms and their relativesBristleworms and their relatives

are members of the phylumPolychaeta. Polychaetes are pri-marily marine organisms. Each

segment of a polychaete has manysetae, hence the name (polychaetemeans “many bristles”). This classincludes bristleworms, lug worms,plumed worms, sea mice, and fanworms, shown in Figure 27.11. Eachbody segment of a polychaete also hasa pair of appendages called parapodia,which can be used for swimming orcrawling over corals and the bottomof the sea. Parapodia also function ingas exchange. A polychaete has ahead with well-developed senseorgans, including eyes. Eyes rangefrom simple eyespots to larger eyescarried on stalks.

LeechesLeeches are segmented worms

with flattened bodies and no setae.Although these animals can be foundin many different habitats, mostleeches live in freshwater streams orrivers. Unlike earthworms, mostspecies are parasites that suck bloodor other body fluids from the bodiesof their hosts, which include ducks,turtles, fishes, and people. Front andrear suckers enable leeches to attachthemselves to their hosts.

You may cringe at the thought ofbeing bitten by a leech, but the bite isnot painful. This is because the salivaof the leech contains chemicals thatact as an anesthetic. Other chemicalsprevent the blood from clotting. Aleech can ingest two to five times itsown weight in one meal. Once fed, aleech will drop off its host. It may noteat again for a year.

752 MOLLUSKS AND SEGMENTED WORMS

CAREERS IN BIOLOGY

Microsurgeon

Would you like to be able to reattach an accident vic-

tim’s hand? Then you might con-sider a career as a microsurgeon.

Skills for the JobMicrosurgeons use high-

powered microscopes and three-dimensional computer technology tosee and repair tiny nerves and bloodvessels. A microsurgeon in ophthalmologymight repair a retina, while other microsurgeons removetumors deep within a brain, or transplant organs.Microsurgeons who reattach hands, feet, and ears often useleeches after surgery to improve blood flow through the reat-tached body part. Microsurgeons must complete four years ofcollege, four years of medical school, three to five years of aresidency program, and special training in microsurgery. Theymust also pass an examination to become certified.

For more careers in related fields, be sureto check the Glencoe Science Web Site.

www.glencoe.com/sec/science

OriginWORDWORD

parapodiaFrom the Greekwords para, meaning“before,” and podion,meaning “foot.”Polychaete wormsmove using fleshy,paddlelike flapscalled parapodia.

Figure 27.11The fan worm trapsfood in the mucus onits “fans.” Distur-bances in the water,such as a change in thedirection of the currentor the passing by of anorganism, cause theseworms to quickly with-draw into their tubes.

752

Courses in high school:advanced science and math-ematics courses

College: bachelor’s degree, med-ical degree, hospital residency,training in microsurgery

Career IssueSkill in microsurgery allows sur-geons to perform amazing repairsand corrections. Discuss with stu-dents whether all surgeons shouldbe required to complete trainingin microsurgery.

For More InformationFor more information aboutbecoming a surgeon or microsur-geon, students might write to:

American College of Surgeons55 East Erie StreetChicago, IL 60611

Visual LearningVisual-Spatial Ask studentsto compare the fan worm in

Figure 27.11 with the earthwormin Figure 27.10. Use the photo ofthe fan worm to emphasize thatnot all segmented worms live interrestrial habitats.

Skill Have students exam-ine Figure 27.12 and create a cir-cle graph that includes all thespecies of segmented worms andmollusks within the 360° circle.Ask them to indicate the portionof the total number of specieseach group contains by drawinglines inside the circle. When theyhave completed the graph, askstudents to identify what per-centage of the total is representedby gastropods and by cepha-lopods. Ask them to make a hypo-thesis about the reason for therelative sizes of these two groups.L2

P

LS

AssessmentAssessment

L1

P

LS

CAREERS IN BIOLOGY

Ask students to visit a bait shop and findout where and how the shop gets bristleworms and earthworms, how they care forthem, and what kinds of fishes are caughtusing these worms as bait. Have studentsgo fishing with these worms as bait andreport to the class.

P

LS

L1

P

LS

CD-ROMBiology: The Dynamics of LifeBioQuest: Biodiversity Park

Disc 3, 4

Resource ManagerResource Manager

Basic Concepts Transparency48 and Master

Reinforcement and StudyGuide, p. 122

Content Mastery, pp. 133,135-136 L1

P

LS

L2

P

LS

P

ELL

LS

L1

P

LS

753

PLAN THE EXPERIMENTPLAN THE EXPERIMENT

1. As a group, make a list of pos-sible ways you might test your hypothesis. Keep the available materials in mind as you plan your procedure.

2. Be sure to design an experi-ment that will test one variable at a time. Plan to collect quan-titative data. Make sure to incorporate a control.

3. Record your procedure and list materials and amounts you will need. Design and construct a data table for recording your findings.

Check the PlanDiscuss the following points

with other group members.

1. What data will you collect, and how will they be recorded?

2. Does each test have one variable and a control? Whatare they?

3. Each test should include mea-surements of some kind. Whatare you measuring in each test?

4. How many trials will you runfor each test?

5. Assign roles for this investiga-tion.

6. Make sure your teacher hasapproved your experimentalplan before you proceed further.

7. Carry out your experiment.CAUTION: Return earth-worms to the container theteacher has provided.

27.2 SEGMENTED WORMS 755

1. Checking Your HypothesisWhich surface did the worm prefer? Explain.

2. Interpreting Observations Inwhich temperature was the wormmost active? Explain.

3. Observing and Inferring Howdid the earthworm respond tolight? Of what survival value isthis behavior?

4. Observing and Inferring Howdid the earthworm respond to dryand moist environments? Of whatsurvival value is this behavior?

5. Drawing Conclusions Were your

hypotheses supported by yourdata? Why or why not?

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

Safety PrecautionsBe sure to treat the earthworm in a

humane manner at all times. Wet yourhands before handling earthworms.Always wear goggles in the lab.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

Going FurtherGoing Further

Project Based on your experiment, designanother experiment that would help toanswer a question that arose from your work.You might want to try other variables similarto the ones you used, or you might choose toinvestigate a completely different variable.

To find out more aboutsegmented worms, visit

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

YOUR OWNDESIGN

YOUR OWNDESIGN

Student answers may vary.1. a rough surface; the worm

moves more easily on a roughsurface

2. an intermediate temperature;an earthworm is ectothermicso its level of activity dependsupon the surrounding tem-perature

3. moved away from light;earthworms are safer frompredators in the soil where itis dark

4. preferred a moist environ-ment; earthworm’s skin mustremain moist or the animalwill dry out and die

5. Students who made hypothe-ses that the worms wouldprefer moist environments,intermediate temperatures,darkness, and rough surfacesmost likely would have theirhypotheses supported bydata.

Performance Ask studentsto design and then carry out anexperiment to determine howearthworms respond to gravity.Use the Performance Task Ass-essment List for Designing anExperiment in PASC, p. 23. L2

P

LS

AssessmentAssessment

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

755

bottom of a pan may be covered with soil.Part of the pan may be covered with apiece of black construction paper while apenlight is shone on the other side. Theamount of time a worm spends in thelight and dark sides of the container maythen be measured.

■ To determine the worm’s preference forheat or cold, the glass pan could be

placed on top of two culture dishes—onecontaining warm tap water and the othercontaining ice.

Data and ObservationsMost likely, earthworms will avoid light andextremes of temperature, move quickly on arough surface, and prefer a moist surface.

Going FurtherGoing Further

Have students design similarexperiments for other inverte-brates and compare their resultswith those obtained for theearthworm. L3

P

LS

How do earthworms respondto their environment?

A n earthworm spends its time eating its way through soil, digestingorganic matter, and passing inorganic matter through the diges-

tive system and out of its body. Because earthworms are dependent on soilfor food and shelter, they respond to stimuli in a way that will ensure acontinuous supply of food and a safe place in which to live. These responsesare genetically controlled. In this BioLab, you will design an experimentto determine the responses of earthworms to various stimuli.

YOUR OWNDESIGN

YOUR OWNDESIGN

ProblemHow do earthworms

respond to light, different sur-faces, moist and dry environ-ments, and warm and coldenvironments?

HypothesesPlace your worm

in a tray with somemoist soil. Watchyour worm forabout 5 minutes,and record what

you observe. Make a hypothesisbased on your observations aboutwhat the worm might do under con-ditions of light and dark, rough andsmooth surfaces, moist and dry sur-faces, and warm and cold conditions.Limit your investigation as timerequires.

ObjectivesIn this BioLab, you will:■ Measure the sensitivity of earth-

worms to different stimuli, includ-ing light, water, and temperature.

■ Interpret earthworm responsesaccording to terms of adaptationsthat promote their survival.

Possible Materialslive earthworms paper towelsglass pan sandpaperculture dishes warm tap waterthermometer water dropper penlightice rulerblack paper cotton swabshand lens or

stereomicroscope

PREPARATIONPREPARATION

754

YOUR OWNDESIGN

YOUR OWNDESIGN

754

Time Allotment One or two class periods

Process Skillsobserve and infer, compare andcontrast, recognize cause andeffect, form a hypothesis, inter-pret data, design an experiment,separate controls and variables

Safety Precautions■ Remind students to treat the

earthworms in a humane man-ner at all times.

■ Make sure that students washtheir hands both before andafter the experiment.

■ Keep earthworms in the refrig-erator overnight, but removethem two hours prior to thelab.

Possible HypothesesStudents may hypothesize thatthe worms will move toward thedark, move faster on a rough sur-face, choose a moist surface overa dry surface, and prefer cool ver-sus warm conditions.

PREPARATIONPREPARATION

P

LS

PLAN THE EXPERIMENTPLAN THE EXPERIMENT

Teaching Strategies■ To save time, have groups test only oneor two variables and share their data.■ Ask students to gently rub their fingersup and down the length of the ventral sur-face of the worms to feel their setae.■ Review the terms anterior, posterior, dorsal,and ventral. Ask students to use these termswhen recording their observations.

Possible Procedures■ To test which surface enables a worm to

move fastest, students may decide to mea-sure how far the worm moves in a givenperiod on surfaces such as sandpaper, thebottom of the dry glass pan, the bottomof a wet glass pan, and on wet and drypaper towels.

■ To test the worm’s reaction to light, the

Resource ManagerResource Manager

BioLab and MiniLabWorksheets, p. 123 L2

P

LS

Chapter 27 AssessmentChapter 27 Assessment

SUMMARYSUMMARY

Section 27.1

Section 27.2

Main Ideas■ Mollusks have bilateral symmetry, a coelom, and

two body openings. Many also have shells andsimilar larvae.

■ Most gastropods have a shell, mantle, radula,open circulatory system, gills, and nephridia.Gastropods without shells are protected by acovering of mucus.

■ Bivalve mollusks have two shells and are filterfeeders. They have no radula.

■ Cephalopods have tentacles with suckers, abeaklike mouth with a radula, and a closed cir-culatory system. They include the octopus,squid, and chambered nautilus.

Vocabularyclosed circulatory system

(p. 744)mantle (p. 742)nephridia (p. 745)open circulatory system

(p. 744)radula (p. 742)

Mollusks

Main Ideas■ The phylum Annelida includes the earthworms,

bristleworms and their relatives, and leeches.They are bilaterally symmetrical and have acoelom and two body openings; some have lar-vae that look like the larvae of mollusks. Theirbodies are cylindrical and segmented.

■ Earthworms have complex digestive, excre-tory, muscular, and circulatory systems.

■ Bristleworms and their relatives are mostlymarine species. They have many setae andparapodia that are used for crawling along.

■ Leeches are flattened, segmented worms.Most are aquatic parasites.

■ Fossil remains of mollusks show that they firstlived 500 million years ago. Fossil records showthat segmented worms first appeared 620 mil-lion years ago.

Vocabularygizzard (p. 750)setae (p. 748)Segmented

Worms

CHAPTER 27 ASSESSMENT 757

1. When an earthworm passes soil through itsdigestive tract, the soil does NOT gothrough the ________.a. stomach c. gizzardb. nephridia d. crop

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS 2. Which of the following does NOT use aradula for feeding?a. snail c. oysterb. slug d. squid

3. Which of the following animals have setae?a. snails c. earthwormsb. clams d. squids

757

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

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

1. b2. c3. c

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS

Chapter 27 AssessmentChapter 27 Assessment

All ChapterAssessment

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

Resource ManagerResource Manager

Chapter Assessment, pp. 157-162MindJogger VideoquizzesComputer Test BankBDOL Interactive CD-ROM, Chapter 27

quiz

The present Is the key to the past Becausemollusks are generally well preserved in the fossil record, abundant, easy to recognize, andwidely distributed geographically, they are excel-lent index fossils. Index fossils, together with their modern relatives, can be used to hypothesizeabout ancient climates and environments.

Mollusk shells can also provide informationabout the biotic, physical, and chemical changesthat occur in an ecosystem. Modern mollusks, for example, have been used to determine the source and distribution of various aquatic pollutants.

Mollusks as timekeepers Mollusks can also be thought of as marine timekeepers. A molluskshell grows only along one edge. The pigmentedpatterns produced by the animal along this grow-ing edge rarely change. Thus, the pattern pro-duced is not only specific to the species but alsois a space and time record of the shell-producingprocess of that particular organism.

Mollusk shells can also be used to determinean exact age because these structures contain the radioactive element strontium. By measuringthe amounts of different isotopes of strontium in

the shell, scientists are able to compute theexact age of the organism, and, by exten-

sion, the exact age of the rocks containing the shell.

ConnectionEarth ScienceEarth Science

Connection Mollusks as Indicators

The fossil record shows that variousspecies of ammonites lived from about

230 million years ago to about 66 millionyears ago. Ammonites are now extinct. Do

you think these mollusks are good index fossils?Explain your answer.

To find out more about mollusksand other index fossils, visit the

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

CONNECTION TO BIOLOGYCONNECTION TO BIOLOGY

Fossilized mollusk shells

“Finally, the shells in the Peuquenes or oldestridge, prove, as before remarked, that it has beenupraised 14 000 feet since a Secondary period…”

—Charles Darwin, in The Voyage of the Beagle

Although a few species of mollusks live onland, most mollusks are marine or fresh-

water organisms. How is it, then, that on one ofhis journeys to South America, Charles Darwinfound aquatic mollusk shells thousands of feetabove sea level? This observation by the famousnaturalist helped to support Darwin’s hypothesisthat Earth has changed over time.

Mollusks once ruled earth Mollusks firstappear in Earth’s fossil record more than 500million years ago. By 30 million years later, theseshelled creatures had become the dominant lifeform on Earth. Thousands of species of mollusksevolved to fill available niches. Yet, numerousspecies of mollusks became extinct at the close ofthe Mesozoic era 66 million years ago. Today, theestimated number of mollusk species rangesbetween 50 000 and 130 000.

756

PurposeStudents will learn how molluskscan be used to determine ancientclimates and environments aswell as radiometric ages.

Teaching Strategies■ Provide students with anassortment of fossil molluskshells as well as living examples ofthese organisms. Allow studentsto use hand lenses to observe thediversity in these organisms,especially the shells. If actualspecimens are not readily avail-able, provide students with color photographs of mollusks.Challenge students to classify theexamples based on the relation-ship between the organisms’shells and soft body parts.Students should be able to iden-tify organisms as belonging to thegastropod, bivalve, or cephalopodgroups.■ Explain, if necessary, themethod of absolute dating.Certain radioactive elementsdecay at a constant rate called ahalf-life. By measuring theamount of the original elementleft and the amount of its decayproduct, the age of a specimencan be determined.■ Have a volunteer explain theobservation made by Darwin.Students should recount that theshells were deposited in a body ofwater, probably an ocean. Earthprocesses, including uplift,caused this area of land, whichwas once below sea level, to beraised thousands of feet above theocean’s surface.

Connection to BiologyMost students should be able todeduce that ammonites are, infact, excellent index fossilsbecause they are readily pre-served as fossils and lived for ageologically relatively shortperiod of time.

P

ELL

LS

L2

P

LS

P

LS

ConnectionEarth ScienceEarth Science

Connection

Internet Address Book

Note Internet addressesthat you find useful in

the space below for quick reference.

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

Disc 3

VIDEOTAPEMindJogger Videoquizzes

Chapter 27: Mollusks and Segmented WormsHave students work in groups as they playthe videoquiz game to review key chapterconcepts.

Chapter 27 AssessmentChapter 27 Assessment

CHAPTER 27 ASSESSMENT 759

25. Compare nephridia in mollusks and segmented worms.

26. Observing and Inferring Explain why thephylogeny of worms is not as well under-stood as the phylogeny of mollusks.

27. Recognizing Cause and Effect Explain how bivalves in salt marshes are importantfor the health of the other species that live there.

28. Observing and Inferring Suppose there areso many Anodonta clams in a stream that thefish population is reduced. How could youcontrol the clam population without harmingthe fish?

29. Recognizing Cause and Effect Bivalvescalled scallops can escape from predators byclapping their shells together and forciblyexpelling water. What structures in a bivalveallow scallops to behave in this manner?

30. Concept Mapping Complete the conceptmap by using the following vocabulary terms: mantle, closed circulatory system,open circulatory system.

THINKING CRITICALLYTHINKING CRITICALLY

ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

The graph below shows how a number ofdifferent animals respond to light.

Using a Graph Study the graph and answerthe following questions.1. Which animals spend more time in the

light?a. A, C, D c. A, B, C, D, Eb. B, E d. C, D

2. Which animals do not spend as muchtime in the light?a. A, C, D c. A, B, C, D, Eb. B, E d. C, D

3. Which animals might be nocturnal?a. A, C, D c. A, B, C, D, Eb. B, E d. C, D

4. Which animals might live under a rock?a. A, C, D c. A, B, C, D, Eb. B, E d. C, D

5. To which animal group might an earth-worm belong?a. A c. Cb. B d. D

6. Making a Graph Make a graph of thefollowing data. Animal A spends 20 min-utes in the dark. Animal B spends 15minutes in the dark. Animal C spendstwo minutes in the dark. Animal Dspends seven minutes in the dark.

Animals

Tim

e in

min

utes

spen

t in

light

A B C D E

1

2

3

4

5

6

7

8

Response of Various Animals to Light

shell

have a

Mollusks

either/or

that provide oxygento body cells

that secretes a

foot 1.

2. 3.

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

CD-ROM

759

25. Nephridia remove metabolicwastes from an animal’s body.In segmented worms there arenephridia in each segment.Mollusks usually have one ortwo nephridia.

26. Soft-bodied worms do not fos-silize as readily as mollusks,which have hard shells.

27. Bivalves filter organic matterfrom the water and break itdown to smaller units that canbe used by marsh grasses andalgae.

28. Answers will vary. Students maysuggest introducing a clampredator or a chemical to killglochidia.

29. abductor muscles, incurrent andexcurrent siphons

30. 1. Mantle, 2. Open circulatorysystem, 3. Closed circulatory sys-tem

THINKING CRITICALLYTHINKING CRITICALLY

Chapter 27 AssessmentChapter 27 Assessment

1. a2. b3. b4. b5. b6.

Chapter 27 AssessmentChapter 27 Assessment

4. The ________ is a thin membrane that surrounds the internal organs of a mollusk.a. foot c. mantleb. shell d. siphon

5. Oysters, clams, and scallops are ________.a. gastropods c. cephalopodsb. bivalves d. nematodes

6. Snails, slugs, and limpets are ________.a. gastropods c. bivalvesb. cephalopods d. cestodes

7. A ________ is the tonguelike organ thatassists gastropods to obtain food.a. foot c. siphonb. shell d. radula

8. Which of the following word pairs are mostclosely related?a. filter feeding—radulab. scraping algae—siphonc. predation—tentacled. nephridia—gizzard

9. Which of the following is a gastropod?

a. c.

b. d.

10. Animals with bilateral symmetry, a coelom,two body openings, a muscular foot, and amantle are ________.a. segmented worms c. mollusksb. flatworms d. roundworms

11. In an open circulatory system, the bloodmoves through vessels and into ________around the body organs, whereas in a closed circulatory system, the blood remains in vessels.

12. The cephalopods circulate blood in a(n)________ circulatory system.

13. This example of a cephalopod is the only animal of that group with a(n) ________.

14. Segmented worms and mollusks both havebilateral symmetry, a coelom, and similar________.

15. Animals distinguished by cylindrical bodiesand ringed segments are ________.

16. ________ are excretory structures that removewastes from an earthworm’s body.

17. Annelids are probably most closely related to ________ because they have similar larvae.

18. During mating, two earthworms exchange________.

19. Segmented worms with flattened bodies,suckers, and no bristles are called ________.

20. The saliva of leeches contains chemicals thatact as a(n) ________.

21. Compare how a cnidarian and an octopus usetheir tentacles to capture food.

22. Describe how sponges and bivalves have asimilar way of obtaining food.

23. Why is it a good idea to keep a snail in anaquarium?

24. Compare the protective adaptations of gastropods and cephalopods.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

758 CHAPTER 27 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

What does the test expect of me?Find out what concepts, objectives, or standardsare being tested beforehand and keep those con-cepts in mind as you solve the questions. Stick towhat the test is trying to test.

758

4. c5. b6. a7. d8. c9. c

10. c11. open spaces12. closed 13. external shell14. larvae15. segmented worms16. Nephridia17. mollusks18. sperm19. leeches20. anesthetic

21. Cnidarian tentacles containstinging cells that immobilizeprey, and octopus tentacleshave suckers for capturing prey.

22. Sponges and bivalves are filterfeeders that strain food fromwater currents.

23. Snails scrape algae from sur-faces with their radulas.

24. Gastropods can withdraw intotheir shells. Bivalves can closeup their shells. Cephalopods,such as squids, can swim veryfast, and the octopus can use itstentacles for defense.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

Chapter 27 AssessmentChapter 27 Assessment

Response of VariousAnimals to Dark

Response of VariousAnimals to Dark

Tim

e in

Dar

k (m

inut

es)

0A B C D

5

10

15

20