Download BIOL 2015 – Evolution and Diversity

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
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Trochozoa
Lophophorata
Figure2.AphylogenetictreebasedonDNAdata.Dunnetal.2008.
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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.
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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.
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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.
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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).
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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.
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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.
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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.
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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.
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