Download BIOL 2015 – Evolution and Diversity

BIOL2015–EvolutionandDiversity
Lab7:Porifera,CnidariaandCtenophora
Introduction
Intermsofknownlivingorganisms,animalsarethemostspeciousgroupoforganismsonEarth.They
comeinawidevarietyofshapes,sizes,andstructure.Infact,thereareover35phylaofanimalsanditis
acontinuingchallengeforbiologiststounderstandboththephylogeneticrelationshipsamonganimals
andtheevolutionaryprocessesthatproducedthegreatdiversityweseetoday(amodernphylogenetic
treeisshowninFigure1).
Thereareafewunderlyingthemesinanimalevolutionwhichyoushouldkeepinmindduringthenext
seriesoflabs.Tworelatedthemesare:
1. EvolutionofMotility.Theabilitytofindfoodandescapepredationisanimportantpartoflife
formostanimals.Motilitywasakeyinnovationandisfoundinthemajorityofanimals.
2. AdvancedHeterotrophy.Sophisticatedmeansofpreycaptureallowanimalstoconsumelarger
quantitiesofdifferentkindsoffood.Muchofthediversityevidentinanimalscomesfrom
differentwaysanimalshaveevolvedtoobtainfood.
Animalsaremulticellularheterotrophs.Thatis,theyaremadeofmanycellsandtheydon’tmaketheir
ownfood.Thesimplestanimals,thesponges,donothaveagutandcannotmoveinsearchoffood.
Theyhaveevolvedapump-likemechanismtomovenutrientssuspendedinwaterpasttheindividual
cellsthatmakeuptheirbody.Asnutrientspassthesecellstheyaretakenupviaendocytosisand
digestedwithintheeachcell.Mostanimalsmoveaboutinsearchoffoodandhaveagutwithinwhich
digestioncanoccur.Thistypeofdigestioniscalledextracellulardigestionanditenablesthemto
consumelargerfooditems.Theabilitytomove,theabilitytocapturelargerfooditems,andtheability
toavoidbeingeaten,areallaidedbylargerbodysizesandrequireanextensive“infrastructure.”For
example,senseorgansandanervoussystemareimportantfortheprocessingsensoryinformationand
thecoordinationofmovement.Otherimportantsystemsincludeasystemforgaseousexchange
(respiratorysystem),asystemformovingmaterialsaroundthebody(circulatorysystem),andsystems
fortheremovalofmetabolicwastes(excretorysystem).Allofthesesystemsarerequiredtokeepa
large,mobileanimalfunctioningproperly.Inthislabwewillintroduceseveralfeaturesofbodyplans
thatarerelatedtotheevolutionoflocomotorability,increasedbodysize,andtheabilitytocaptureand
digestfoodinanimals.Insubsequentlabswewilladdressthesefeaturesofanimalsingreaterdetail.
Otherimportantthemesintheevolutionofanimalsarecenteredinvariousdevelopmentalprocesses
thatleadtotheevolutionofbodyplans.Sinceallofthetissues,organs,andorgansystemsdevelopfrom
asinglecell,anysubsequentchangeinthesefromoneanimaltoanotherwillultimatelydependon
modificationstothedevelopmentalprocessesfromwhichtheyform.
Inthislabwewillexaminesomeofthebasicfeaturesofanimalembryology,andexplorehowmajor
changesinbodyplanscanresultfromdifferencesinthepatternsofearlydevelopment.
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Figure1.PhylogenetictreebasedonDNAdata.Dunnetal.2008.
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Porifera
Sponges(Figure2)arethesimplestanimals
anatomically,lackingmanyofthefeaturesthat
characterizeallotheranimals.However,closestudies
ofboththeirembryologyandtheirgenomesshow
thatspongesarecloselyrelatedtootheranimals,and
nottoanyotherkingdom.
Theapparentsimplicityhasledbiologiststoregard
spongesasprimitiveoffshootsoftheanimallineage,
havingsplitoffbeforetheevolutionofthemore
complexfeaturesthatmostotheranimalsshare.
However,somestudieshavesuggestedthatthe
ancestorsofspongesmayactuallyhavebeenmore
complex.
Thereareabout5,000speciesofspongesworldwide.
Allspongesliveinthewaterandmostaremarine.
Thewallofaspongecontains3typesofcells.The
outercellsareflattenedepidermalcells,called
Pinacocytes.Theinnercells,calledChoanocytes,are
collarcellswithflagella.Itistheconstantmovementof
theflagellathatproduceswatercurrentsthatflow
throughtheporesintothespongocoelandoutthrough
theupperopeningofthebody,calledtheOsculum.
Figure2.Exampleofamarinesponge(Porifera;blue
color)growingbyacoral(Cnidaria;green).We'llobserve
bothgroupstoday.
Amoebocytes(orarcheocytes)arecellswithan
amoeboid,orirregular,shape.Theyperformvarious
functionsandcandifferentiatetobecomeothercell
types.Theamoebocytesarelocatedinthelayercalledthe
Mesohyl.Thisisagelatinouslayerbetweentheouter
epidermalpinacocytesandtheinnerlayerof
choanocytes.Theskeletonofthespongeiscomposedof
tinyneedle-likesplinterscalledSpicules(composedof
silicaorcalciumcarbonate),ameshofproteincalled
Spongin,oracombinationofboth.
Examinethespongeswehaveondisplay.Notethe
followingfeatures:
Figure3.Diagramshowingspongewall.
•
Notruetissues.Spongeslacktheleveloftissue
organizationseeninotheranimals.
•
Nosymmetry.Spongeshavevariableandirregularbodyforms.
•
Intracellulardigestion.Spongecellstakeinsmallfoodparticlesusingphagocytosis.
•
Spicules:Spongesposseshard,crystallinestructures(spicules)inmesohyl.
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Scypha
Scyphaisasmall,tube-shapedsponge.
Findthefollowingslides:
Aslidelabeled"Scyphaspiculestrew"
Aslidelabeled"ScyphaTangentialsec."
Aslidelabeled"Scyphac.s.&l.s."(c.s.=crosssection.
l.s.=longitudinalsection.)
Aslidelabeled"Scyphawitheggs"
Aslidelabeled"Gemmules"
Onthe"Scyphaspiculestrew"slideyoucanseethe
mineralizedskeletalelementsofsomesponges(spicules).
Theyoccurinavarietyofshapesandsizes.Besureyoucan
identifywhattheseare.
Tangentialsection:Thisslidewillshowtheporousstructure
ofthespongebodywall.You’llnoticethattherearemany
openspaces.Theseareeitherincurrentcanals,throughwhich
waterentersthesponge,orradialcanals,throughwhich
waterexitsintothespongocoel(Figure3).Incurrentcanals
arelinedwiththepinacocytes,whichprovidethecanalswith
asmoothsurface.Theradialcanalsarelinedwith
choanocytes.Youmightbeabletoseesomeoftheflagella,
butthecollarsarepoorlypreservedinthesesections.
Crosssectionandlongitudinalsection:Scyphausesthe
flagellaonitschoanocytestodrawwaterthroughitsbodyso
itcancapturesmallsuspendedparticlesoffood.Observethe
structureoftheanimal(Figure4)withitsincurrentandradial
canals,anditsspongocoel(which,bytheway,isnot
comparabletothecoelomofotheranimals,becausethere
arenoorgansinit;it'sjustanemptytubethroughwhich
waterisexpelled).YoushouldfindtheOstia(singularostium),
throughwhichwaterentersthesponge,andtheApopyles.
Apopylesareopeningsthatallowwatertoenterthe
spongocoelaftermovingthroughthespongewall.Whatkind Figure4.Crosssection(top)andlongitudinal
ofcanalendswithanapopyle?
section(bottom)ofScypha.
https://vimeo.com/40240443–Spongefilterfeeding(from
ShapeofLifeseries)
Wehaveanumberofspongeskeletonstolookat,somakesureyouexaminethem.Trytoidentifyas
manyfeaturesaspossibleonthesespecimens.Canyoutellwhatmaterialeachiscomposedof?
SexualReproductioninSponges
Findapreparedslidelabeled"Scyphawitheggs".
Youshouldbeabletoseelargeeggs,whichdevelopdirectlyfromamoebocytes.Modifiedchoanocytes
producesperm,andmostspongesaresequentialhermaphrodites-eggsandspermmatureatdifferent
timeswithinanyindividual.Beabletohypothesizeaboutwhythisreproductivestrategyevolved(rather
thanasimpleformofhermaphrodite)?
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AsexualReproductioninSponges(Gemmules) Findapreparedslidelabeled"Gemmules".
Agemmule(Figure5)isanasexualreproductivesacproducedby
freshwaterspongesthatcontainamassofamoebocytesandare
desiccation-resistant.Manyfreshwaterspongesdieoffinthe
winterandgrowbackinthewarmermonthsasgemmules
"germinate”.Theamoebocyteswithinthegemmulearereleased
throughamicropyle(apore)anddevelopintoanewsponge.
Figure5.Spongegemmules.
Gastrulationinsponges
Gastrulationisthedevelopmentalprocessthatdefinesthebasicembryonictissuelayersinanimalsand
itlaysthefoundationforthelaterdevelopmentofcomplexanimalbodies.Thiswillbecoveredin
anotherlab,laterthissemester.Manysourcesstatethatspongeslackgastrulation,andthuslack
definedembryonictissuelayers.However,manyspongespecialistsbelievethatgastrulationdoesoccur
insponges,althoughtheprocessisquitedifferentfromthatinotheranimalgroups.
Cnidaria
Cnidariacontainsabout11,000speciesthatincludejellyfish,
hydrozoans,coralsandseaanemones.Mostaremarine.TheCnidaria
areclearlydistinctfromotheranimalsbecausetheyhavetentacles
withstingingcellscalledcnidocytes(Figure3).Eachcnidocyte
containsaharpoon-likestructurecalledanematocyst.Whenthe
surfaceofacnidocyteistriggeredbyaprey(orpredator),the
nematocystisfired,whichentanglesandpoisonstheanimal.The
bodyofacnidarianisradiallysymmetricallikeabarrelorawheel.
Cnidariaarediploblastic–amajorevolutionaryinnovation-twocell
layers,ectodermandendodermorgastroderm(so-namedbecauseit
linesthedigestivesac);nervecellsthreadthroughbothofthesetissue
Figure6.Seaanemoneglowingunder
layers.Themostlynon-cellularlayerbetweenectodermand
UVlight.
endodermiscalledmesoglea(middlejelly)andissecretedbythe
cells.
https://www.youtube.com/watch?v=6zJiBc_N1Zk–Nematocystfiring
Themouthiscentralandissurroundedbytentacles.It
leadsintothegastrovascularcavity.Thistwo-partword
referstothetwochieffunctionsofthe
cavity,digestionandcirculation.Therearenoblood
vesselstodistributenutrientsfromdigestionandthe
gastrovascularcavityextendsoutintoeachofthe
tentacles.Gasexchangeoccursbetweencellsandthe
surroundingenvironmentsotherearenospecial
respiratorystructures.
ManymembersoftheCnidariahaveatwo-partlifecycle
thatincludesasessile(attached)polypthatreproduces
asexuallyandafree-swimmingmedusathatreproduces
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Figure7.CrosssectionofHydra.
sexually,withbothstagesbeingdiploid.Thefree-swimmingstagedistributestheoffspringawayfrom
parent,aphenomenoncalleddispersal.TherearethreeclassesofCnidaria:Hydrozoa,Schyphozoaand
Anthozoa.
Hydrozoa
Hydra
ExaminethelivespecimensofHydralittoralis(brownhydra)andChlorohydraviridissima(greenhydra
hassymbioticalgae).Youcanseethebasalattachmentdisc,thebody,andthetentacles
withcnidocytessurroundingthemouth.Suchanattachedlifestageiscalledapolyp.Hydracanglide
slowlyonitsbaseorsomersaultbybendingandplacingthetentaclesonasubstrate.
Findaslidelabeled"Hydrac.s.&l.s."(seefigure7).
LookfortheEpidermiscoveringtheoutsideandGastrodermisontheinsidefacingtheemptytubeof
theGastrovascularCavity.Betweenthesetwolayersofcellsisaline,theMesoglea,whichisusually
thininpolyps.Theepidermishastallepithelio-muscularcells.Themaincellsofthegastrodermisare
nutritive-muscularcells.
https://www.youtube.com/watch?v=elnpe5u4RZ0–Hydrafeeding
AsexualReproduction
Findaslidelabeled"Hydraadultwithbud".
Hydrabuddingshowsthemode
ofasexualreproductioninthisorganism.Beableto
identifyahydrabudding.Intheseslidesyoumightbe
abletoobservetriggeredcnidocytes(Figure8)with
theirdischargednematocytes.Ifyoufollowthe
nematocytebacktothetentacleyoumightobserve
thecnidocyte.
Figure8.TentaclesofHydrawithcnidocytes.
SexualReproduction
Findslideslabeled"Hydraearlyovaryc.s."and
"Hydratestisc.s.".
Hydracrosssectionshowsmaleandfemalegonads-testesandovaries.OnFigure9,testes(left)
protrudeoutfromthebodywallofHydra,andyoucan
seethestainednucleiofmanysmallspermcells.Ovaries
(right)thickenthebodywallandwraparoundthe
tube;eggsarelargerandfewerthansperm.
Alsonotethetwocelllayers,theectodermand
gastroderm,withmesogleabetweenthemandtheempty
gastrovascularcavityinthecenterofthecrosssection.
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Figure9.Testes(left)andovaries(right)ofHydra.
Obelia
Thisgenusisahydrozoanthatexhibitsasortof
“alternationofgenerations”inthatthereisanattached
polypstageandfree-swimmingmedusastage.
Findtheslidelabeled"Obeliahydroidw.m.".
Obeliaisacolonialhydrozoan.Ithasachitinousouter
covering,andtwokindsofpolyps–feedingpolyps(with
tentacles,Figure10-left)andreproductive
polyps(withbuds,Figure10-right).Thereproductive
polypsformephyrae(immaturemedusae)inaprocess
calledstrobilation,whichisatypeoftransversefission. Figure10.ColoniesofthepolypstageofObelia.Realize
thatinHydrozoans,bothgenerationsarediploid.
Ephyraeformconsecutiveplatesattheendofthe
reproductivepolypthatdevelopandultimatelybreak
away(Figure11).Medusaisthesexualstageinthe
lifecycleoftheseorganisms.
Findaslidelabeled"Obeliamedusae".
Eachmedusaiscup-shapedandrimmedwith
tentacles.Themouthhangsdownfromthemiddle.
Foursymmetricallyplacedmassesinthebodyare
thegonads.Afteraneggisfertilized,thezygote
developsintoanewObeliacolony.
Figure11.MedusaeofObelia.Thegonadsarethefour
massessymmetricallyplacedbythemouth.
Scyphozoa
Aurelia
Forscyphozoansthedominantlifestageisthemedusa(Figure
12)butmostscyphozoansalsoretainatleastabriefsessile
polypoidstageand,likeObelia,itsmedusaeareproducedby
strobilation.
ExaminethepreservedspecimensofAureliaunderthe
dissectingmicroscope.
Youshouldobservethisspecimenunderthedissecting
microscope.Identifyfortheoralarms,thetentacles,the
gonads,radialcanals,andthemouth.Gametesarereleased
fromthemouthbywayofgastricpouches,thoughinsome
species,theeggsarefertilizedinthefemale'sgastricpouch,and
arelaterreleasedtotheoutside.
Figure12.Anatomyofajellyfish.
Findtheslidelabeled"Aureliaephyraw.m."
ThisslideshowsanAureliaephyra.Theephyrahaseightshort"arms"insteadoftheumbrellashapeof
anadult.Latergrowthwillfillinthegapsbetweenthearms.BeabletoidentifytheAureliaephyra.
https://vimeo.com/40232821–Aurelia(MoonJelly)lifecycle(fromShapeofLifeseries)
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Anthozoa
CoralsandSeaAnemones
Coralsandseaanemonesaremarineorganismsthatliveattachedtorocksor
otherhardsubstratesandfeedonsmallfishandinvertebrates.Familiarcorals
arecolonial,reef-formingorganisms.Theepidermisofcoralssecretearocklikeskeletalsupportofcalciumcarbonate.Whenpolypsbuildontopofthe
skeletonsofcorals,areefmayultimatelybeformed.
Anemonesaresoftbodied,solitarypolypslikethepreservedspecimensof
Metridium.Thegastrovascularcavityhasaseriesofradialpartitionscalled
septathatgreatlyincreasetheinternalsurfaceareaforabsorptionof
nutrients.AnemonescanbemuchbiggerthanHydra.Theexternalskeletonof
coralsalsoprovidessupportforsuchpartitions(Figure13).
Observetheaquariumslocatedinthelab.Canyouidentifyallthecoralsfrom
theanemonesinthefishtanks?Makesuretocheckthelivingexamplesofthe Figure13.Smallcoralshowing
radialsepta.
aquariumsofRoom170,asthere’snothinglikeseeinglivespecimens.
Findtheslidelabeled"Metridiumc.s.&l.s."
Onthisslideyoucanfindthemouth,tentacles,pharynx
andgastrovascularcavityonthelongitudinalsection.Find
theseptaincrosssection(Figure14).Theterminusofthe
elongatedpharynxiscalledasiphonoglyph,whichis
coveredwithadenselayerofcilia.Siphonoglyphsfunction
tomovewaterandfoodintothegastrovascularcavity.The
cellsoftheseptahavecnidoblastsandsecretedigestive
enzymesforextracellulardigestionoffoodwithinthe
gastrovascularcavity–importantadaptationsbecause
Anthozoanscommonlytakeintheirpreywholeandalive.
Figure14.1.Siphonoglyph,2.Retractormuscle,3.
Primaryseptum,4.Pharynx,5.Gastrovascular
cavity.
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Ctenophora
Ctenophores(Greekfor"comb-bearers")have
eight"combrows"offusedciliaarrangedalong
thesidesoftheanimal,clearlyvisiblealongthe
linesinFigure15.Theseciliabeat
synchronouslyandpropelctenophoresthrough
thewater.Somespeciesmovewithaflapping
motionoftheirlobesorundulationsofthe
body.Manyctenophoreshavetwolong
tentacles,butsomelacktentaclescompletely.
Ctenophores,variouslyknownascombjellies,
seagooseberries,seawalnuts,orVenus's
girdles,arevoraciouspredators.Unlike
cnidarians,withwhichtheyshareseveral
superficialsimilarities,theylackstingingcells.
Instead,inordertocaptureprey,ctenophores
Figure15.Mnemiopsissp.
possessstickycellscalledcolloblasts.Inafew
species,specialciliainthemouthareusedfor
bitinggelatinousprey.Hopefullywewillhavelivespecimensforyoutoviewthisweek.Pleasenotethat,
ifweareunabletogetany,youarestillresponsibleforknowingabouttheseorganisms.
https://www.youtube.com/watch?v=bW3sqB7RTIc–Mnemiopsissp.(fromMontereyAquarium)
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