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Chapter11
MolluscanSuccess
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Evolu4onaryPerspec4ve
• Triploblas4c• Coelomate• Verysuccessful
– 100,000livingspecies• Rela4onshipstootheranimals
– Lophotrochozoans
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Figure11.1Evolu4onaryRela4onshipsofMolluscstoOtherAnimals.
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Table11.1.
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MolluscanCharacteris4cs1. Bodyoftwoparts:head-footandvisceralmass2. Mantlethatsecretesacalcareousshellandcoversthevisceralmass3. Mantlecavityfunc4onsinexcre4on,gasexchange,elimina4onofdiges4ve
wastes,andreleaseofreproduc4veproducts.4. Bilateralsymmetry5. Trochophorelarvae,spiralcleavage,andschizocoelouscoelomforma4on6. Coelomreduced7. Opencirculatorysystem(exceptCephalopoda)8. Radulausuallypresent
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BodyOrganiza4on• Head-foot
– Elongate– Mouth– FootforaWachmentandlocomo4on
• Visceralmass– Dorsaltohead-foot– Organsofdiges4on,circula4on,reproduc4on,excre4on
• Mantle– Enfoldsbody– Secretesshell
• Mantlecavity– Gasexchange,excre4on,elimina4onofdiges4vewastesandreproduc4ve
products• Radula
– Supportedbyodontophore– Raspingfood
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Figure11.2Molluscanbodyorganiza4on.
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Figure11.3Molluscanshellandmantle.
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Figure11.4Radularstructure.
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ClassGastropoda• Snails,limpetsandslugs• 35,000livingspecies• Torsion
– 180ocounterclockwisetwis4ngofvisceralmass,mantle,andmantlecavityduringdevelopment
– Possibleadap4vesignificance• Headentersshellfirst.• Cleanwaterentersanteriorlyorientedmantlecavityopening.
• Mantlesensoryorgansmovetoheadregion.
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Figure11.5TorsioninGastropods.(a)Apretorsiongastropodlarva.(b)A\ertorsionthediges4vetractisloopedandmantleopensnearhead.(c)Hypothe4caladultancestorpriortotorsion.(d)Modernadultgastropoda\ertorsion.
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ClassGastropoda• Shellcoiling
– Earliestfossils,oneplane– Modern,asymmetrical
• Morecompact• Internalorgansasymmetricalandsome4mesnolongerpaired
• Locomo4on– FlaWenedfoot– Ciliapropelovermucoustrail– Muscularwaves
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ClassGastropoda• Feedinganddiges4on
– MostscrapealgaeandaWachedorganisms– Herbivores,predators,scavengers– Diges4vetract
• Ciliated• Foodincorporatedintomucousmasscalledprotostyle.
• Gasexchange– Oneortwogillsinmantlecavity– Landsnails(pulmonates)
• Mantlecavityrichlyvascularforgasexchangewithair
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Figure11.6Gastropodstructure.
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OtherMaintenanceFunc4ons• Opencirculatorysystem
– Bloodbathes4ssuesinsinuses.– Heart
• Singleventricleandsingleauricle– Func4ons
• Transportsnutrients,wastesandgases• Hydraulicskeleton
• Nervoussystem– Sixgangliaplusnervecords
• Sensorystructures– Eyesatbaseorendoftentacles– Statocystsinfoot– Osphradiainmantlecavity
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OtherMaintenanceFunc4ons
• Excre4on– Singlenephridium
• Resultofshellcoiling– Dischargesintomantlecavityoradjacenttomantlecavity(pulmonates)
– Ammonia(aqua4cspecies)– Uricacid(pulmonates)
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Reproduc4on• Dioecious
– Externalfer4liza4on• Eggsshedsinglyorinmasses• Somedioeciousmarinespecies
• Monoecious– Copula4onforinternalfer4liza4on
• Spermtransfermaybemutualorone-way.• Eggsshedinstringsorinmasses
– Larvalstages• Trochophore• Veliger–foot,eyes,tentacles,shell
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GastropodDiversity• Subclasses
– Prosobranchia• 20,000species• Mostlymarine
– Opisthobranchia• 2,000species• Mostlymarine• Seahares,seaslugs• Shell,mantlecavity,andgillsreducedorlost
– Pulmonata• 17,000species• Freshwaterorterrestrial• Vascularmantlecavityservesaslung
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Figure11.7Varia4onsintheGastropodBodyForm.
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ClassBivalvia
• Clams,oysters,mussels,scallops• 30,000species• Shellandassociatedstructures
– Singleshellconsis4ngoftwohingedvalves(figure11.8)
– Mantlesheetlikeandcoverslaterallycompressedbody.
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Figure11.8InsideViewofaBivalveShell.
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GasExchange,FilterFeeding,andDiges4on
• Sedentaryfilterfeeders– Lossofheadandradula– Expansionofcilia-coveredgillsintofoldedsheets(lamellae)
• Ciliacreatewatercurrentsintoandthroughmantlecavity.
– Gasexchangeinwatertubes(figure11.9)– Foodtrappedalonggillsurfaceandtransportedtofoodgroovesandlabialpalps(figure11.10).
– Diges4on(figure11.11)• Crystalinestyleandgastricshield
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Figure11.9Lamellibranchgillofabivalve.Bluearrowsshowwatermovement.Redarrowsshowbloodmovement.
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Figure11.10Bivalvefeeding.Solidpurplearrowsshowpathoffoodpar4cles.Dashedpurplearrowsshowpathofpar4clesbeingrejected.
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Figure11.11Bivalvestructure.
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OtherMaintenanceFunc4ons• Opencirculatorysystem
– Mantleandgillsoxygenateblood
• Nephridia– Belowpericardialcavity– Opentosuprabranchialchamber
• Nervoussystem– Threepairsofinterconnectedganglia– Sensoryreceptorsatmantlemargin
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Reproduc4onandDevelopment
• Mostlydioecious• Gonadswithinvisceralmass• Mostlyexternalfer4liza4on• Trochophoreandveligerlarvalstages(figure11.13a,b)
• FreshwaterinfamilyUnionidae– Parasi4clarvalstage– Glochidium(figures11.13cand11.14)
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Figure11.12BivalveCircula4on.
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Figure11.13Trochophore(a)andveliger(b)larvalstages.Glochidiaofanunionidbivalve.
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Figure11.14Mantlelureofafreshwaterbivalve(Lampsilisreeviana).
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Figure11.15aBivalveDiversity.Giantclam(Tridacnadersa).
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Figure11.15bBivalvediversity.Rockscallop(Hinnitesgiganteus).
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Figure11.15cBivalvediversity.Thegoeduck(Panopeagenerosa).
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ClassCephalopoda
• Squid,octopuses,cuWlefish,andnau4luses• Footmodifiedintocircleoftentaclesorarmsandincorporatedintosiphon
• Headinlinewithvisceralmass• Muscularmantle(figure11.17)
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Figure11.17Internalstructureofthesquid,Loligo.
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prior written consent of McGraw-Hill Education.
ClassCephalopoda• Shell
– Reducedorabsentexceptinnau4lus• Locomo4on
– Jetpropulsionusingmusclesofmantlecompressingwaterwithinmantlecavityandsiphon
• FeedingandDiges4on– Predators
• Tentacles,jaws,radula– Diges4vetractmuscularwithlargediges4veglands
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Figure11.18Cephalopodarmsandtentacles.
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OtherMaintenanceFunc4ons• Closedcirculatorysystem• Nervoussystem
– Largebrains– Complexsensorystructures
• Eyes• Statocysts
• Chromatophores– Colorchangesinvolvedwithcourtshipandotherdisplays
• Inkglands
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Figure11.19Thecephalopodeye.
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Learning
• Unparalleledincomparisontoanyotherinvertebrateandmanyvertebrates
• Evolvedinresponsetopredatorylifestyles
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Reproduc4onandDevelopment
• Dioecious• Maleproducesspermatophores
– Transferstofemale’smantlecavityusingmodifiedtentacle(hectocotylus)
• EggsdepositedsinglyorinmassesaWachedtosubstrate.
• Eggstendedbyparents.
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ClassPolyplacophora• Chitons• Reducedhead,flaWenedfoot,shellconsis4ngofeightdorsalvalves,muscularmantleextendsbeyondmarginofshell(figure11.20)
• FeedonaWachedalgae• Ladderlikenervoussystem• Dioeciouswithexternalfer4liza4on
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Figure11.20ClassPolyplacophora.(a)Tonicellalineata.
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ClassScaphopoda
• Toothshellsortuskshells• Marine,burrowing• Conicalshellopenatbothends• Dioeciouswithtrochophoreandveligerlarvae
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Figure11.21ClassScaphopoda.
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ClassMonoplacophora
• Marine• Undivided,archedshell• Broad,flatfoot• Seriallyrepeatedpairsofgillsandfootretractormuscles
• Dioecious• Embryologyunknown
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Figure11.22ClassMonoplacophora.
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Figure11.23ClassSolenogastres
ClassSolenogastres
• Marinesubstrates• Lackshell• Crawlonventralfoot• Minutecalcareousspicules
• Carnivores
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ClassCaudofoveata
• Deepsea• Wormlike• Feedonforaminifera• Lackshell,foot,andnephridia• 120species
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FurtherPhylogene4cConsidera4ons
• Morethan500millionyearsold• Lophotrochozoa• Shellandmuscularfootnotancestral
– Solenogasterspiculesmaybesimilartoancestral“shell”.
– MuscularfootfirstseeninPolyplacophora.
• Quicklydiversifiedintomodernclasses(figure11.24)
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Figure 11.24 Molluscan Phylogeny.
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