phylum platyhelminthes -...
TRANSCRIPT
Phylum PlatyhelminthesThe “flat” “worms”
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Section21.4
PhylumPlatyhelminthes(flatworms):Planarians,flukes,andtapeworms
FlatwormsHaveBilateralSymmetry
Figure21.2
Section21.4 Figure21.12
Keyfeatures
FlatwormsHaveBilateralSymmetry
Section21.4 Figure21.12
Diversity
FlatwormsHaveBilateralSymmetry
Flatworm: ©Leslie Newman & Andrew Flowers/Science Source; planarian: ©Carolina Biological Supply Company/Phototake; fluke: ©Volker Steger/Science Source; tapeworm: ©Biophoto Associates/Science Source
ClassTurbellariaincludes:Planarians
ClassCestodaIncludes:Tapeworms
ClassTrematodaIncludes:Flukes
Section21.4 Figure21.13
Anatomy
FlatwormsHaveBilateralSymmetry,DorsoventrallyFlattened,andlackaskeleton
• Theyhavethreegermlayers:• Ectoderm: Outside• Endoderm: Inside• Mesoderm:Middlelayeroftissuebetweentheectodermandtheendoderm
• ThoughFlatwormshavethreegermlayerstheyareacoelomates andhavenobodycavity(thinkofyour
normalsandwich)
• Flatwormsdohavetrueorgans andprimitiveorgansystems thatareusedfordigestion andexcretion
• Flatworms are also the most primitive organisms to show cephalization.
• The head region of Flatworms contains a concentration of nerve tissue called ganglia (singular=ganglion) that resembles a primitive brain.
Cephalization
¨ Theyhavetwonervecords thatrunfromtheganglia intheheadregionalongtheventral sideofthewormtothetaleregion
¨ IntheheadregionofFlatwormsaretwoeye-spots¨ Theyalsohavelobesonthesideoftheirhead
calledauricles(Primitiveear)
Auricles
Feeding• Flatwormshaveamouth/anus whichisconnectedtothegastrovascularsystem throughalongmuscularpharynx.
• Smallinvertebratesortheremainsofdeadanimalsaretakenintothemouth/anusbythemuscularpharynx
• Thefoodisthendigestedinthehighlybranchedgastrovascularcavity
• Thenutrientsmovesfromthegutintothebodycellsbydiffusion
Respiration
• Respirationoccursbydiffusion duetoacoelomatebodyplan(superflat)
InternalTransport• Nutrients andoxygen inthegutaresimplyabsorbedintothebodycellsbytheprocessofdiffusion
Excretion
• Mostundigestedfoodisreleaseddirectlyoutoftheanus/mouth:Pharynx
• Aflamecell isaspecializedexcretorycell• Flamecellsfunctionlikeakidney,removingwastematerials.• Thebeatingofciliaresemblesaflame,givingthecellitsname.
NerveResponse¨ Flatwormsareabletosenseandrespondtoatleast
threeformsofstimuli:¡ Senseandrespondtolight:Theeye-spots candetectlightandallowtheFlatwormstorespondtoit
¡ Senseandrespondtochemicals: Pits onthesideoftheirheadregionscansensechemicals inthewaterandallowtheFlatwormstorespond(like“smelling”)
¡ Senseandrespondtotouch:Theauricles oneithersideoftheheadregioncansensetouch andallowtheFlatwormstorespond
• Theganglia intheheadregionrelaymessagesfromthesensoryorgansdownthenervecords totherestofthebody.Thenervecords cancontrolmuscles inthebodywhichallowtheFlatwormstomove oreat.
Auricles
Movement
• Theflatwormsmoveacrossasurfaceusingcilia ontheirventralsurface
• Theycanalsomovebycontractingcircular andlongitudinalmusclesthatlayjustbelowtheectoderm.Thesemusclesarecontrolledbythenervecords.
Reproduction
• AsexualReproduction:• Flatwormscanasexuallyreproducethroughaprocesscalledfission.Theanterior andposterior endsholdasurfaceandthemidsectionconstricts.Thisresultsintwonewflatworms,onefromtheanterior endoftheoriginalflatwormandtheotherfromtheposterior endoftheoriginalflatworm.
Reproduction• Flatwormscanalsoregenerate partstheyhavelost.
Regenerationvideo
Planaria Regeneration
• Planarians will spontaneously detach the tail end of their bodies and each half will regenerate into a full size flatworm
• Planarians can be cut either transversally (shown above) or dorsally and most will regenerate into a full size worm
Super Cool Fact: the smallest piece of planarian to ever regenerate in a lab into a new planarian was 1/279th of a planarian! That’s approximately 10,000 cells!
• SexualReproduction:• Flatwormsarehermaphroditic, butmostpracticecrossfertilization
• Aftertwoflatwormshavecopulatedtheyreleasecocoonoffertilizedeggs andattachthemtoasurface
StructurestoKnow/IdentifyinPlanarianEyespotsAuriclesCiliatedEpidermallayer(ventralsideonly)PharynxGastrovascularCavityGangliaVentralNerveCordTransverseNerveCordFlamecellAKAProtonephridiaEggTesteSeminalreceptacleGenitalPoreOviductOvary
ReviewSymbioticRelationships:• Symbiosis:twospecieslivingtogetherwithanotherorganismincloseassociation
• 3Types:
MUTALISM PARASITISM COMMENSALISM
ParasiticTrematoda:TheLiverFluke
LiverFlukeLifeCycle
• Adultsliverflukeslivesintheliverofsheep• Eggsarepassedintointestineandmixw/feces• Eggspassedfromfecesfromsheepandfallintowater.• Eggembryonatesanddevelopslarvaecalledmiracidia• Miracidiainfectswatersnails• Miracidiagoesthroughmultiplestagesbeforedevelopsintocercaria(swimminglarvae).
• Cercarialeavesnailandformacystscalledmetacercariaandgeteatenbycattle• Metacercariaburrowsthroughtissueandtravelstoliverandmatesandcyclerepeats
LifeCycleofLiverFluke
LiverFlukeLifeCycle
Parasitic FlatwormsThe pork tapeworm – Taenia solium
• Infectspigsandhumans• Livesintheintestineofitshostandpasseseggsthroughthefeces
• Highlyadaptedtoconstantinternalenvironments
• Lackssensoryorgans,coordinationformobilityandadigestivesystem
• Haveamodifiedepidermis“tegument”whichprotectsagainstthedigestiveenzymesandtheimmunesystemsofthehost
• Canreach7minlengthinhumans!• Areflatandlongwhichmaximizesabsorptionofnutrientsfromthehost
SupercoolFlatwormFact• thelargesttapewormeverreportedwasinaspermwhaleandwas98feetinlength!
Tapeworm Scolex
ParasiticFlatworms:Tapeworms
• Thetapewormhasananteriorendcalleda scolex withcomplicatedhooks forattachingtotheintestinesofitshost.
• Thetapewormdoesnothaveamouthordigestivesystem.• Insteadtheybathinthepre-digestedfluidsoftheirhostandabsorbnutrientsdirectlyintotheirbodycells
• Why?Evolutionaryadvantage?• Moreroomforreproductivestructures- everyProglottidhascapabilityofbecominganothertapeworm
Proglottids
Hooks
Scolex
Suckers
Rostellum
The tapeworm “up close and personal….”
• Theheadendhasascolexwithfoursuckers(twoseenhere)thathelpitattachtotheintestineofitshost
• Thebodyisseparatedintosectionscalled“proglottids”thathousehighlydevelopedreproductivesystems(darkenedareas)capableofproducinghundredsofthousandsofeggsandsperm
Platyhelminthes:Cestoda(Tapeworm)
GeneralAnatomy
Taenia solium.
LifecycleofaTapeworm
Summarizing Identifying Characteristics of the Phylum Platyhelminthes• Acoelomate• Exhibit bilateral symmetry• Have a bilateral nervous system with cephalization at the
head end. Some species exhibit eyespots sensitive to light• Possess a Gastrovascular Cavity (GVC) and primitive
organ systems for digestion and excretion• Do not have a circulatory or respiratory system but do
take in O2 through their body surface (integumentary exchange)
• Hermaphroditic : can reproduce sexually (do not self fertilize) or asexually by regeneration
• Are motile and utilize an undulation form of motion• Found in marine, freshwater and damp terrestrial habitats