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BIOL2015–EvolutionandDiversity Lab9:Lophotrochozoa–PartI: Platyhelminthes,Rotifera,Bryozoa,andBrachiopoda Introduction Lastweekwestudiedtheporiferaandthecnideria.Spongeslacktruetissueandanysymmetrical organizationofthebody,whilecnideriahastruetissue(withtwogermlayers)andradialsymmetry. Todaywebeginthestudyoftheanimalswithbilateralsymmetry(Bilateria).Allbilateralanimalshave threegermlayers(endoderm,mesodermandectoderm).Thebilateriaaredividedintotwomajor groups(seeFigure1),theprotostomesandthedeuterostomes(thesenamesrefertowherethemouth formsintheearlyembryo.SeeFigure32.7ofyour2010textbook). Theanimalphylogenyhasbeen revolutionizedinthelast15years bymolecularphylogeneticstudies, whichhavechangedmanyofthe acceptedrelationshipsthatwere basedsolelyonmorphologicaldata. Onesuchgroupisthe Lophotrochozoa(Figure1),which arealargegroupofanimalswithin theprotostomesandwillbeour focusforthenexttwolabs.Figure2 showsamoredetailedphylogenyof themajorgroupsinthe Lophotrochozoa–theyarediverse! ThenameLophotrochozoacomes fromthenamesofthetwomajor animalgroupsincluded:the Figure1.Asimplifiedphylogenetictreeofanimals. LophophorataandtheTrochozoa. Trochozoa:Manyofthemembersareworm-like,thoughnotallofthemarefamiliarorcommon.The twolargestgroupsoftrochozoansaretheMollusca(mollusks)andtheAnnelida(segmentedworms). Itmightseemstrangeatfirsttogroupearthwormsandsquidstogether.Theycertainlydon'tlookmuch alike,butthatisonlytruewhenlookingattheadultform;theyshareafundamentalfeatureoftheirlife 1 Trochozoa Lophophorata Figure2.AphylogenetictreebasedonDNAdata.Dunnetal.2008. 2 history.Manyannelidsandmolluskssharepatternsofdevelopmentinearlyembryonicstages.When theirlarvaehatch,eachisamicroscopicswimmerknownasatrochophorelarva.Thelarvahastwo bandsofciliaaroundthemiddlethatareusedforswimmingandforgatheringfood,andatthe"top"isa clusteroflongerflagellae.Sothelarvaeofthesegroupsarenearlyidentical,eventhoughtheymature intoverydifferentadultforms.Untilveryrecently,theArthropoda(insects&crustaceans)were consideredcloserelativesoftheAnnelida,basedonthefactthatbothgroupsaresegmented,butno arthropodhasatrochophorelarvaandnomolecularstudiessupportacloserelationshipbetweenthem. Lophophorata:ThisgroupincludesthephylaPhoronida,Entoprocta(bothsmallgroups),Bryozoa (formerlycalledEctoprocta)andBrachiopoda,withthelattertwohavinganextensivefossilrecord.The featuresharedbythisgroupisthelophophore,anunusualfeedingappendagebearinghollowtentacles. WhiletheLophophorataareawell-recognizedgroup,phylogeneticstudiesdonotyetagreeonthe identityoftheirclosestrelatives.TheseanimalswereonceincludedinthePseudocoelomata,because theydonothaveadistinctinternalbodycavityliketheTrochozoa,butthisgroupingdoesnothold togetherinmodernstudies. Platyhelminthes(Flatworms) Flatwormsareanatomicallysimplecomparedtonematodesandannelids.Theylackcirculatoryand respiratorysystems.Manymembersofthisphylumareparasitic(e.g.,flukesandtapeworms)butthere arealsoanumberofspeciesthatarefree-living,liketheplanarianswewillhaveinlabthisweek.These non-parasiticPlatyhelminthesarefoundinfreshwater,marineandinsometerrestrialenvironments andarefuntowatch. Flatwormfeatures: • Threetissuelayersinembryo.Almostallanimalssharethisbasicfeature;thespongesand cnidariansareexceptions. • Acoelomate:Flatwormsdon'thaveanykindofcoelomorpseudocoelom;theirbodiesare basicallysolid.Thissimplebodystructureledbiologiststobelievethatthephylum Platyhelminthesbranchedofffromtherestoftheanimalsbeforetheevolutionofthecoelom. However,newphylogeneticstudieshaveledsomeresearcherstoconcludethatflatworms descendedfromanancestorthathadacoelom,andlaterlostthecoelom. • Gastrovascularcavity:Thedigestivetracthasonlyoneopening,andbranchesthroughoutthe body.Flatwormshaveextracellulardigestion,likemostanimals(butunlikesponges). • Pharynx:amusculartubethroughwhichtheflatwormcansuckfoodintoitsgastrovascular cavity.Theopeningintothepharynxcouldbeconsideredthemouth,butsincethisanimalhasa two-waygut,thatopeningalsomustfunctionastheanus. 3 Trepaxonemata Thereareapproximately4,500speciesofplanarians. Mostarefree-livingandmarine,althoughyoucan alsofindtheminfreshwaterandonland.Manyare predators,theyfeedonprotozoans,small invertebratesordeadanimals.Thecanclone themselvesbylongitudinalortransversal partitioning;theyarealsohermaphrodites. Dugesia(Planarians) ObservelivingDugesiaatadissectingmicroscope.Noticetheflattenedbodiesoftheseanimals,and theirgracefulmovements.Athickmucouscoatinganddenselyciliatedepidermisontheirventralside allowsthemtoglidealongsurfaces.Also notethattheyhavea“head-end”where photosensitiveeyespotsorocelliare located(lendingtheDugesiaa"cross-eyed" appearance),whichhelpthemavoidbright light. Findthefollowingslides: • • • Figure3.AwholemountviewofaPlanaria. Findapreparedslidelabeled"Planariaw.m.". Findapreparedslidelabeled"Planariacombinationw.m.". Findapreparedslidelabeled"Planaria c.s.". Thisspecimenisstainedtohighlight thegastrovascularcavity,showingthesmall branchescalleddiverticula.Notethatthereis onemainbranchofthegastrovascularcavityin theanteriorpartofthebody,buttwomain branchesposteriortothepharynx. Theeyespotsaresimpleanddon'tforman image;that'swhytheyarecalledeyespots insteadofeyes.However,theyareslightlycupshapedandfacetowardthesides.Withthis arrangement,theflatwormcantelllightfrom darkandmovetowardthedark.Cup-shaped Figure4.Cross-sectionviewsofPlanaria. 4 eyesarejustonestepinthetransitionfromphotoreceptivecellstoeyeballs. Planariacrosssections:ThismicroscopeslidehasseveraldifferentcrosssectionsofaPlanaria,showing differentregionsofthebody.Ontheventralsurfacesyoucanobserveciliausedforlocomotion. Anteriorregion:Thissectionanteriorto(infrontof)thepharynx.Thebodyismoreorlesssolid;theonly openingsarethediverticulaofthegastrovascularcavity. Pharynxregion:Thiscrosssectionshowsthepharynx,whichisretractedintothepharyngealcavity(the emptywhitespacesurroundingthe pharynx).Thepharynxitselfisathick, musculartube;whenPlanariaeats,it evertsthepharynx,stickingitoutofthe bodytosuckupbitsoffood. Posteriorregion:Thegastrovascularcavity isdividedintotwomainbranches,with smallerdiverticula.Theverticalpinklines aredorsoventralmuscles. Figure5.Cross-sectionoftheposteriorregionofPlanaria. Trematoda(Flukes) TheflatwormsoftheclassTrematoda,alsocalledflukes,areinternalparasitesofmollusksand vertebrates.Thereareapproximately18,000to24,000species.Theyhaveoralsuckers,sometimes supplementedbyhooks,withwhichtheyattachtotheirvertebratehosts.Trematodeshaveretainedthe samebodyformanddigestivecavityastheturbellarians.However,practicallytheentireinterioris occupiedbythereproductivesystem;theseorganismsarecapableofproducinghugenumbersof offspring.TrematodesoftheorderDigeneahavecomplexlifecyclesinvolvingtwoormorehosts.The larvalwormsoccupysmallanimals,typicallysnailsandfish,andtheadultwormsareinternalparasites ofvertebrates.Manyspecies,suchastheliverfluke Clonorchissinensisandthebloodfluke(Schistosoma), causeseriousdiseasesinhumans. Clonorchissinensis(ChineseLiverFluke) Findapreparedslidelabeled"Clonorchissinensis w.m.". Figure6.AwholemountviewoftheChinese liverfluke. 5 Someoftheseslidescontainlargeranimals,somesmallerones–makesuretolookatboth. Findtheoralsucker;theacetabulumorventralsucker;andthepairedandelongateintestines(labeled “gut”inFigure6).Notethatithasreduceddigestivesystemandalso,howmuchofthespacewithinthe adultflukeisdevotedtoreproduction. NoticealsothatTrematodeshavebothmaleandfemalereproductiveorgans(theyarehermaphrodites). Thelargeuterus(nothomologouswithouruterus)isfilledwitheggsandislocatedanteriortothe testes,whichproducesperm.Whydoyouthinkthattheorganisminvestssomuchenergyon reproduction? Fasciolahepatica(CommonLiverFluke) Thecommonliverflukeorsheepliverflukeis globallydistributed,andinfectstheliversof variousmammals,includinghumans.Fasciolahas acomplexlifecyclewithmultipleintermediate stagesandhosts(Figure7).Thediseasecausedby theflukeiscalledfascioliasisandcausesgreat economiclossesinsheepandcattle.Observethe preservedspecimensofFasciolahepaticaon displayandbeabletoidentifyit. Findapreparedslidelabeled"Fasciolahepatica miracidiaw.m.". Fasciolatakeondifferentformsdependingonthe stageoftheirlifecycle.MiracidiaarethefreeFigure7.Fasciolalifecycle. livingmotileform,coveredwithcilia,andsettle intoamolluskhost.Theyaresmallandvariableinform,soobservemorethanone. Findapreparedslidelabeled"Fasciolahepaticarediaew.m."and"Fasciolahepaticametacercaria w.m."toseewhatformthisparasitetakesinitsintermediatehosts(Figure7). 6 Schistosomamansoni-BloodFluke Thisflukecausesthedisease schistosomiasis,whichaffectsmorethan 20millionpeopleayear.Schistosomes areatypicaltrematodesinthattheadult stageshavetwosexes(dioecious)andare locatedinbloodvesselsofthedefinitive host(mostothertrematodesare hermaphroditicandarefoundinthe intestinaltractorinorgans,suchasthe liver).Schistosomeshavetwohosts:a definitivehost(i.e.human)wherethe parasiteundergoessexualreproduction, andasingleintermediatesnailhost wherethereareanumberofasexual reproductivestages. Findapreparedslide(demonstration) Figure8.LifecycleofSchistosomamansoni. labeled"Schistosomamansonimaleand femalew.m.".Youwillobserveapairofmatingflukes.Duringcopulation,thefemaleisheldinaspecial channel(thegynecophoralgroove). Cestoda(Tapeworms) Cestodaisthenamegiventoaclassofparasitic flatworms,commonlycalledtapeworms.Asadults theyliveinthedigestivetractofvertebrates,and ofteninthebodiesofvariousanimalsasjuveniles. Overathousandspecieshavebeendescribed,andall vertebratespeciescanbeparasitizedbyatleastone speciesoftapeworm!Infectioninhumansoccurs becauseofconsumptionofimproperlycookedor processedmeat(pork,beef,orfish,forexample). Taeniasaginata,thebeeftapeworm,cangrowupto 20minthegutofitshost,butthewhaletapeworm, Figure9.ThisisanadultTaeniasaginata Polygonoporusgiganticus,cangrowtoover30m! tapeworm.Whichsideisthehead? Cestodeeggshaveevenbeendiscoveredinfossil sharkfeces(coprolites)datingtothemid-tolatePermian,some270mya. 7 Tapewormslackadigestivetrack.Allnutrientsareabsorbeddirectlythroughthebodysurface.The host’sdigestiveenzymesdoallthework.Theheadregion,orscolex,ismodifiedforattachmenttothe intestinalwall.Thescolexhassuckers,andoftenhasaringofhooksaswell. Mostofthetapeworm’sbodyconsistsofrepeated segmentscalledproglottids(althoughit’snotan exampleoftruesegmentation).Eachproglottidisa self-containedpacketcontainingmostlyreproductive organs.Newproglottidsareproducednearthescolex. Themostmatureproglottidsareattheoppositeendof theanimal. Findthepreparedslideslabeled"Taeniapisiformis scolexw.m."and"Taeniapisiformismatureand gravidw.m.".Ontheformerobservethesuckersand hooks,onthelatterobservehowmuchofthebodyis Figure10.StainedadultTaeniapisiformis. devotedtothereproductivestructures.Alsonotehow the“segments”calledproglottidschangeshapeoverthelengthoftheanimal. Rotifera Bdelloidea Rotiferameans“wheelbearer”.Theyaregenerally microscopic(barelyseenwiththenakedeye),withtwo maindistinguishingfeatures.Thefirstisananterior regioncalledthecoronathatisusedinfeedingandin locomotion.Thesecondisamuscularpharynx(calleda mastax)thatpossessescomplexjawsknownastrophi. Rotifersarepseudocelomates Examinethelivespecimensandthepreparedslidesofa rotifertofamiliarizeyourselfwiththeirfunctional morphology.Notethe3generalregions:head,body andfoot(andtoes).Observealivespecimenat increasinglyhighermagnification,ultimatelyaimingto toes observethepatternofciliationonthecorona. Figure7:Rotifer Asinmanyfreshwaterorganisms,manyrotiferspossess Figure11.Aschematicdrawingofarotifer. 8 remarkableadaptationstowithstandperiodsofdroughtand/orcoldtemperatures.Themostnotableof thesearetheirabilitytoundergoparthenogenesis(growthanddevelopmentofeggswithout fertilization)andproducerestingeggs.Manyspecieshavetheabilitytoundergoanhydrobioisis,a restingstagethatoccursduringdryconditionsinwhichtheanimalcansurvivecompletelydesiccatedfor longperiodsoftime. Findapreparedslidelabeled"Rotifersw.m.".Findthesamestructuresasabove,butalsotrytofindthe stomachandpseudocoel. Bryozoa Phylactolaemata Bryozoa(formerlycalled ectoprocta),means"moss animals”).Theyareageologically importantgroupofsmallanimals. ThevastmajorityofBryozoansare colonialandmostaremarine. Superficiallytheycanresemble corals.Bryozoansaremost abundantintemperate-tropical watersthatarenottooturbid.They requireafirmsubstrateontowhich theyattachorencrust,andclear agitatedwaterfromwhichthey obtaintheirsuspendedfood. Figure12.Aclose-upofaBryozoancolony.Thehorseshoeshapedlophophoresareclearlyvisible. Enclosedwithinaskeletonof calcite,Bryozoanshaveasac-like coelomatebodywithawell-definedmouth,anus,andotherspecializedorgans.Onesuchorganisthe lophophore(aciliatedstructureusedinfoodgathering)thatisattachedtotentaclesthatsurroundthe mouth. Findapreparedslidelabeled"BryozoaPectinatellaw.m.".Beabletoidentifytheorganismandthe lophophores. 9 Brachiopoda Lingulata Whilerecentbrachiopodsarearatherrareandinsignificantgroup,theirlongfossilhistoryshowsthat theywereattimesthemostprominentanimalsintheseas.Consequently,brachiopodsreceiveonly passinginterestfromzoologists,butagreatdealofattentionfrompaleontologists.Thephylumisquite importantforbiostratigraphy,paleoecology,andevolutionarystudiesbecauseitshowsagreatvarietyof changesinformandfunctionthroughtime. Brachiopodsresembleclams,buttheirshellsaredorsal-ventral(thatis,there’satopshellandabottom shell),whereasclamshavelateralshells(there’saleftandarightshell).Brachiopodsfeedusinga lophophorelikeEcoproctans,whichcreatesawatercurrentthatenablesthemtofilterfoodparticlesout ofthewater. FindpreservedspecimensofLingulaondisplay.The genusLingulafirstevolvedover400millionyearago, makingittheoldestlivinganimalgenusthatstill containsextantspecies!Identifytheinternalstructures labeledinFigure13onthepreservedspecimensinthe lab. Figure13.Adissectedbrachiopodshowingthe internalstructure. 10