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BIOL2015–EvolutionandDiversity Lab12:Deuterostomia: Echinodermata,Hemichordata,&Chordata Introduction Inourfinaldiversitylabwewillexaminethedeuterostomes,whichincludethefollowingthreephyla: Echinodermata,Hemichordata,andChordata.Althoughthesephylaseemoutwardlyverydifferent,theyshare commonfeaturesintheirearlydevelopmentthatdistinguishthemfromotherbilaterallysymmetricalanimals. Rememberindeuterostomes,theembryonicblastoporegivesrisetotheanus.Intheprotostomes,which includesannelids,arthropods,andmollusks,theblastoporegivesrisetothemouth.Althoughadultechinoderms haveradialsymmetry,theirlarvaearebilaterallysymmetrical,thustheyareclassifiedalongwithchordatesas bilaterallysymmetrical. Figure1:PhylogenyofAnimalia 1 Echinodermata Thewordechinodermmeansspinyskin.Thesearemarineorganismswithfive-foldradialsymmetry,commonly calledstarfish(ClassAsteroidea),sanddollarsandseaurchins(ClassEchinoidea),seacucumbers(Class Holothuroidea),andsealilies(ClassCrinoidea).Theyarecoelomatesandtheyhaveanendoskeletonthatismade ofcalciumcarbonate,whicharisesfromthemesoderm.Sexesareseparateinechinodermsandfertilizationis external;thereisalarvalstagewithbilateralsymmetry.Auniquederivedfeatureofthegroupisitswatervascularsystem;seawaterispumpedthroughaseriesofductstoworkthetubefeetandthesuctioncupsattheir tips. Asteroidea(Starfish) Findthepreservedstarfishondisplay.On the dorsalsideyoucanseethecentraldisk and radiatingarms.Justoffcenteronthe centraldiskthereisasmallsieve-like plate,calledthemadreporite,which servesastheconduitthroughwhich seawaterentersintothewatervascular system.Smallfleshyextensionsamong the spinesarethesoft,hollowskingillsfor respiration;theycommunicatewiththe coelom.Ontheventralsideofthearms there areambulacralgroovesthatarefilledwith the fleshytubefeet.Tubefeetandskingills are Figure2:Starfish bothusedforgasexchangeandexcretion of nitrogenouswaste.Themouthisinthecenteroftheventralside.Echinodermsmovebyalternatingthesuction andreleaseoftubefeet.Asteroidscanregeneratelostordamagedarms,ifenoughofthecentraldiscisintact. Anisolatedarmsoondies(thereisanexception,knowninonegenuswhereanarmcanregeneratetherest). Useadissectingmicroscopetofindthepincer-likepedicellariaethatprojectfromthesurfaceofthedermis. Examineanopenedstarfishandnotethelargecoelom.Findtheampullaeatthebasesofthetubefeet,andthe ringandradialcanalsofthewatervascularsystem. Observethelivingstarfishintheaquariumandnoticethemovementsoftheirtubefeet. Ophiuroidea(brittlestars) Findthepreservedbrittlestarsondisplay.Organsareconcentratedinthelargecentraldiskbecausetheyhave longslenderarms.Brittlestarsprimarilyusetheirarmstomovewithspeedandagility.Somebrittlestarsare carnivoreswhileothersarefilterfeeders. Examinethedorsalsurfaceandnoticetheabsenceofamadreporite.Ontheventralsurface,noticethat ossiclescovertheambulacralgroovesandthatthemouthissurroundedbyfivemoveablejawplates.The bursalslits(whichradiatearoundthemouth)openintosacsinwhichwaterconstantlycirculates,andgas exchangeoccurs. Findthelivingbrittlestarsinthedisplaylargeaquariumandnotewheretheyresidewithintheaquarium. Echinoidea(SeaUrchins,SandDollars) Echinoidshaveashellmadefromwell-developeddermalossicles.TheTubefeetlinetheambulacralregions, buttheambulacralgroovesareclosed.Pedicellariaearepresent,likestarfish.Seaurchinsmoveslowlyacross thesubstrateconsumingsmallanimalsorscrapingalgaeoffofrockswithpowerful,plate-linedjaws.Observe 2 thelivingseaurchinsinRoomthelargetankandnoticehowthespinesmove(musclesatthespine’sbase controlstheirmovement). Examinethepreservedseaurchinsondisplay. Examinethepreservedsanddollarsondisplay.Notehowtheshellisflattened.Beabletoidentifythe differentechinoids. Holothuroidea(SeaCucumbers) Althoughtheyareechinoderms,seacucumbershavesoftskinthanotherechinoderms.Allthatremainsoftheir calcareousskeletonsaresmallspicules.Theirambulacralregionsextendfrommouthtoanus,andthe ambulacralgroovesareclosed.Modifiedtubefeetcalledcircumoraltentaclessurroundthemouth.The pedicellariaeseeninotherechinodermsareabsent.Findthelivingseacucumbersinthemainaquariumin Room170,andobservethecircumoraltentacles. Examinethepreservedseacucumbersondisplay. Hemichordata Hemichordatesaresmalltomediumsizedmarinewormsandarerepresentedbythreeextantclasses, Enteropneusta(acornworms),Pterobranchia(small,deepwaterworms),andPlanctosphaeroidea(knownonlyby larvaofonespecies).Enteropneustaisthemostspeciousofthesethreeclassesandisrepresentedbyabout70 species.ThiswillbetheonlyHemichordatewehaveforyoutoexamineinlab. Enteropneusta(acornworms) Ofthechordatecharacteristics,acornworms haveonlypharyngealslits.Theyfeedon detritusandburrowinsoftmarinesediments. Findthepreservedacornwormondisplayand observe(begentile–theyarefragile)the proboscis,thecollar,thetrunkandthe pharyngealslits. Figure3:AcornWorm 3 Chordates ThePhylumChordatacontainsthreesubphyla,Cephalochordata,Urochordata,andVertebrata(sometimescalled Craniata).WewilllookattheCephalochordata,thelancelets.AnotherSubphylumistheVertebrata;Fish, amphibians,reptiles,birds,andmammalsareallvertebrates.Amphioxusismostlikelythedescendantfroman earlystageinchordateevolution,anditshowsallfiveofthedefiningcharacteristicsofchordates: 1. 2. 3. 4. 5. notochord pharyngealslits endostyleorthyroidgland dorsalhollownervecord post-analtail Allchordatesshowthesecharacteristicsatsomestageintheirlifetimes.Youwillalsonoticefeaturesthatare commonamongmanyanimalphyla,includingbilateralsymmetry,coelom,andbodysegmentation(seeninthe seriesofmuscleblockscalledmyomeres).Thecirculatoryanddigestivesystemsareseparate. Thefirsttwosubphyla,CephalochordataandUrochordata,areoftenreferredtocollectivelyasthe Protochordates,meaningthefirstChordates.Whileall5synapomorphiesarepresentinthesetwosubphyla, somepersistthroughouttheentirelifespanoftheorganismwhileothersaretransientandareonlypresentinthe larvalstate. Cephalochordata(Amphioxus) Althoughtheyspendmostoftheirtimeburiedinthe sandfilterfeedingonsmallfoodparticles,lanceletsare small,'fish-like'animalsandaredecentswimmers. FindthepreservedAmphioxusondisplay.Thereis relativelylittlecephalizationinlancelets,butyoumay observeasmallenlargementattheanteriorendofthe dorsalnervechord.Likevertebrates,butunliketunicate larvae,thetrunkmuscleshavemyomeres(segmented structures).Theendostyle(aciliatedgrooveinthe pharynx)isusedtotrapfoodparticlesandtransport themtothestomach.Alsoobservethenotochordand theatriopore,whichistheequivalentoftheexcurrent siphonoftunicates,andtheanusandpostanaltail. Findapreparedslidelabeled"Amphioxusimmature w.m."and"Amphioxusimmatureadultw.m." Figure4:Lancelet 4 Findallthechordatefeaturesontheimmatureslide (youmaynotbeabletoseetheendostyle).Theadult slideshowsthepharyngealslitsandtentacles(cirri) better.Youshouldalsobeabletolocatetheforwardpointingcecumofthedigestivetract.Whatdoesthe cecumdo? Findapreparedmicroscopeslidelabeled "AmphioxusPharynxandGonadsec." Findthenotochord,dorsalnervecord,pharynxwith gillbarsandgillslits,andthelargemuscles.You shouldtrytofindtheendostyleatthebottomofthe pharynx,andtrytodistinguishtheatriumfromthe coelom. Figure5:Lancelet 5 Urochordata(Tunicates) Ascidiacea Althoughurochordatesmaylookabitlikespongesintheiradultlifestage,theyarecurrentlythoughttobethe sistergroupofvertebrates.WhymightthesebethebettersistergrouptoVertebrates?MostUrochordatesare hermaphroditicandusecross-fertilizationtoreproduce.Somehaveasingletestisandsingleovary(whenboth gonadsarecombinedintoasinglemassitisoftencalledtheovotestis)andarelocatedintheloopofthegut. Somespeciespossessmanygonadsthatareembeddedintheconnectivetissuelayerofthebodywall.Solitary speciesareoviparousandtheireggshaveverylittleyolk.Eggsarereleasedthroughtheatrial(excurrent) siphonandarefertilizedexternally.Incontrast,mostcolonialspeciesareviviparousandtheireggshave significantamountofyolk.Gestationtakesplaceineithertheoviductorwithintheatriumitselfandthe lecithotrophictadpolelarvaearethenreleasedfromtheatrialsiphon. Findthepreservedseasquirtsondisplay(CionaandMolgula).Observetheoral(incurrent)andatrial (excurrent)siphonsinCiona(youdon’tneedtodistinguish theminMolgula). Findthelivingseasquirtsinthesmallerdisplayaquarium. Trytoobservewatermovementaroundthesiphons. Findapreparedmicroscopeslidelabeled"Ecteinascidia w.m." Usethe4Xobjectivetoobservetheseadultanimals.Find thesiphons,theverylargepharynxwithitsconspicuous perforations. TheAscidiantadpolelarvaearelecithotrophicandtherefore obtainalltheirnutrientsfromtheyolk.So,dependingonthe amountofyolk,thelarvalstagecanbeextremelyshort rangingfromafewminutestoabout36hours.Itisduringthis stagethatallfiveChordatecharactersareevident.Someof theChordatecharactersarelostasthetadpoleundergoes metamorphosisandtransformsintothesessilefilter-feeding Figure6:Ciona adultthatwearefamiliarwith. Findapreparedmicroscopeslidelabeled"AscidianTadpolew.m." Thetatpolesaresmallanditisdifficulttoidentifymanyoftheinternalstructures.Findthepostanaltailand thenotochord. 6 Vertebrata UnfortunatelywedonothaveenoughtimetoreallyexplorethediversityoftheVertebrates,whichisthemost speciousgroupwithinDeuterostomia.ThoughwewillnotbegoingintomuchdetailIthoughtitwouldbefunto atleastmakeasuperficialsweepoverthemajorvertebratetaxonomicalgroups.Fortunately,vertebratesare usuallymorefamiliartothevastmajorityofpeopleandarethereforemucheasiertolearnandremember.Since wedonothavetimetogointomuchdetailwiththevertebratesIhavechosen1to2unifyingmorphologicalor functionalthemesforeachofthemajorvertebrateclassesthatwecanexploreduringourfinallaboratory session. Agnatha:Jawlessvertebrates Myxini(Hagfish)andCephalapidomorphi(Lamprey) Hagfishareentirelymarineandaremajorscavengersonsunkenvertebratecarcasses.Althoughthey arehighlyspecializedinmanyrespects,hagfishesarethoughttobethemostprimitiveliving vertebrates.Theabsenceofboneinthegroupisatrulyprimitivecondition. Adultlampreysarehighlypredaceousfishesthatattachthemselvestotheexternalsurfaceofother fishesandscrapethefleshoftheirpreywithamodified“tongue.”Lampreyevolvedfromanimportant groupoffishesthathadheavybonyplatesintheirskin.Duetothesecondarylossofbone,thereare almostnofossillampreys. ExaminethepreservedHagfishandLamprey.Findtheeyes,mouth,andthepharyngealopeningson bothorganisms.Whatarethemostobviousdifferencesbetweenthesestructuresonthesetwo primitivevertebrates?Whyarethesestructuressodifferent? Gnathostomata:Jawedvertebrates Chondrichthyes-Sharks,rays,skates,ratfish Mostofthevertebratesinthisgroupwillprobablyfamiliartoyou.Theylackabonyskeletonbutoften elementsoftheirskeletonwillcalcifyformingcalcifiedcartilage.Itissimilartoboneinthatitis mineralizedandisthereforestrongincompression,howeveritisdifferentfromboneinmanyways. Onebigfunctionaldifferenceisthatcalcifiedcartilageisnotdynamic,meaningthatitcannotremodel itselfwhentheloadingregimeschange–somethingbonedoesexceptionallywell. Sharksaretheonlyfishthathaveplacoidscales.Placoidscalesareverydifferentthanallotherfish scales.Theyaremadeofdentin,coveredwithenamel,andhaveapulpcavity,makingthem morphologicallysimilartoteeth.Infact,developinacontinuouslinewiththeteethandcoverthe entiresurfaceofthebody. Findtheslideentitled“Placoidscale”.Trytoidentifytheenamel,dentin,andpulpcavityontheplacoid scale.Thereisalsoalaminatedphotoyoucanlookatthatshowstheseregions. Compareandcontrastthefollowingfeaturesforthepreservedchondrichthyanspecimensinlab: generalbodyform sizeandshapeoffins positionofgillslits,spiracleandeyes Howdothesefeaturesrelatetodifferencesinlifehabit? 7 Actinopterygii–Ray-finnedfishes Actinopterygianfishesareanincrediblydiversegroupofvertebrates.Theyfirstappeared500millionyears ago.ThemoreprimitiveactinopterygiansarewithinthegroupHolosteiwhilethemorederived actinopterygiansarewithinthegroupTeleostei. Holostei Holosteansarethemostprimitiveoftheray-finnedfishes.Theyhaveverysturdyskullswithteethon allthebonesformingthejaws.Comparethejawsoftheholosteanswiththoseoftheteleostfishes. Teleostei OfalltheordersassociatedwithActinopterygii,theTeleostsarethemostdiverseanddominatethe fishfaunasofbothfreshandmarinewaters.Theprimaryreasonoftencitedforthedominanceof Teleostfishistheinnovationofanewtypeofsuctionfeeding,onethatismadepossiblebyachangein theshapeofthemouthcoupledwithextrememobilityinspecificjawbones.Forclarificationpurposes, itisthemoreadvancedTeleoststhathavethemorphologicalfeaturesnecessarytosuctionfeed,which aredescribedintheparagraphbelow.PrimitiveTeleostsdonotsuctionfeedandthereforemust capturepreywiththeirteeth. AdvancedTeleostshaveevolvedamoreroundedgapeandtheabilitytoprojecttheirpremaxillae.As theclosedmouthispushedforwardthevolumeoftheoralcavityincreaseswhilethepressurewithin theoralcavitydecreases.Whenthemouthisopenedthepreyitemandthewatersurroundingitis rapidlytransportedintothemouthaswatermovesfromhightolowpressure.Thustheyareableto capturepreywithoutactuallygrabbingaholdofit.Oneoftheconsequencesofthisnewmodeof feedingisthatadvancedTeleostsnolongerhaveteethonthemaxillae.Thisallowsthemaxillaetoact asleverarmsthatcauseprojectionofthepremaxilla.SomehighlyadvancedTeleostsareevenmore specializedbecausetheyhavelostteethonthedentaryandpremaxillaeaswell.Canyoucomeupwith anexplanationforwhyteethmightbeproblematicforsuctionfeeding? Examinethefishskullsandidentifythebonesofthejawjoint.Canyoudeterminewhichisthemost primitiveandwhichisthemostderived? Sarcopterygii–Lobe-finnedfishes Lungfish(Dipnoi)andtheCoelacanth(Actinista)aretheonlylivingrepresentativesoftheSarcopterygian fishes.Athirdgroupofsarcopterygians,Rhipidistia,isancestraltothefirsttetrapodsandtherefore representsanimportantgroup. Rhipidistia ThefeaturethatlinksRhipidistiatothestemamphibiansisavery distincttoothmorphologycalledthelabyrinthodonttooth(see illustrationtotheright).Inadditiontothistoothtype,theRhipidistian fisheshadmuscularfinsthatcontainedrobustbonyelements (characteristicofSarcopterygianfishes),whichareverydifferentfrom theflimsyfinassociatedwiththeActinopterygianfishes.Itisthe muscularfinandtherobustboneswithinthemthatservedasa preadaptationfortheabilitytosupportthebodyonland. ExaminetheCoelacanthphotointheTimeLifebookentitledThe Fishes.Notethefleshyfinstructure. 8 Tetrapoda:Vertebrateswithfourlimbs Amphibia TheclassAmphibiaincludesmanygenerathatarenowextinct.Duetolimitedtimewewillnotbe consideringanyoftheextinctmembersofthisgroup.Instead,wewillfocusourattentionontheclade knowasLissamphibia(lissos=smooth,amphi=both,bios=life),the“smooth-skinned”amphibians. Lissamphibia-Salamanders,frogs,andcaecillians Allmodernlissamphibiansarethoughttostemfromacommonancestrywithinthelabyrinthodonts. Threedistinctorders:Urodela,Anura,andApodaareincludedwithinthesubclass.Detailedstructural characteristicsoftheinnerear,teeth,andlimbsaresharedbyalllissamphibiansandservetounitethe group. Caudata–Salamandersandnewts Caudatesaretailedamphibians,whichincludethesalamandersandnewts.Unlikeanurans,thebody buildofcaudatesisfairlygeneralized(comparelimbandtrunkproportionswiththoseofthefrog). Caudatesmaybeaquaticorfullyterrestrial.Someofthelargeraquaticsalamandersfailto metamorphosecompletelyandretainsuchlarvalfeaturesasexternalgillsintoadulthood. Anura–Frogsandtoads Frogsandtoadsareamongthemostspecializedtetrapods,especiallyintheirmodesoffeedingand locomotion.Fusionofthetailvertebraeintoasinglerod-likebone(urostyle),elongationofthehind limbs,andshorteningofthetrunkareallcharacteristictraitsofanurans.IncontrasttoUrodeles,there isgenerallyawell-developedeardrum. Gymnophiona–Caecillians Caeciliansareoftenmistakenforeelsorearthworms.Theyshownotraceoflimbsorgirdles,hencethe nameApoda(“nofeet”).Aburrowinglifestyle(possessedbycaecilians)isusuallyaccompaniedbylimb reductionorloss,aswellasreducedeyesoreyesight.Mostcaecilianshaveverypooreyesight,some lackeyesentirely,hencethecommonnamecaecilian(fromcaecus,meaningblind).Unlikefrogsand salamanders,caecilianshaveasolidandcompactskull,usefulforburrowing.Theyarerestrictedto damp,tropicalhabitats;someareentirelyaquatic. Examinetheskeletalspecimensofthefrogandsalamander.Whichpartsofthefrogskeletonare highlyspecializedforitsdistinctivemodeoflocomotion? Amniota Reptilia ThoughtheReptilesareaparaphyleticgroup,itisconvenienttousebecausethenameisfamiliartomost people.Wewillincludethebirdsinthissectiontomakeitmoreaccurate.Themostimportantinnovation withinthisgroupofanimalsistheamnioticegg,whichallowedanimalstomakeacompletebreakfrom thewater.Wewillstartwiththeturtles,whichareoneofthemorebasalgroupsofreptilesaccordingto molecularevidence. 9 Testudines–Turtles Turtles(Testudinata)aretheonlysurvivingreptileswithanapsidskulls(withoutfenestrations;compare withcrocodilianskull).Theyarequitespecializedinsuchfeaturesastheirrigidshell(which incorporatestheribs,vertebrae,andsternalelements),andthecompleteabsenceofteeth. Squamata–Snakesandlizards LizardsandsnakescomprisetheorderSquamata.Snakeshaveevolvedfromprimitiveburrowing lizards.Evidentagain,aburrowinglifestyleoftenleadstolimbreduction,orabsence.Snakesdiffer fromlizardsinmanydetailsoftheiranatomyotherthanabsenceoflimbs(somelizardsarelikewise limbless).Forexample,lizardshavemoveableeyelidsandanexternalauditorymeatus(opening), charactersthatsnakeslack. Archosauria Thiscladeincludesthecrocodiliansandthebirds.Thoughthesetwogroupsareonlydistantlyrelated, molecularevidencesuggeststhattheyareclosertooneanotherthantheyaretothesquamates(lizards andsnakes)andthetestudines(turtles). Crocodylia–Crocodilesandalligators TheorderCrocodylia(sometimesspelledCrocodilia)isrepresentedbycrocodilesandalligators,the groupalsoincludescaimansandgavials.Thecrocodiliansareoneofthefewgroupsofanimalsthat readilythinkofhumansasapreyitem.Thecrocodilianskullisnotlikeanyotherlivingreptile. Examinethecrocodylianandiguanidskulls.Disregardingthesizediscrepanciesbetweenthem,what featuresaredifferent?Trytocomeupwithanexplanationforthedifferencesyousee. Aves–Birds Almostallbirds,fromalbatrossestozebrafinches,allbelongtotheSuperorderNeognathae(meaning newjaw),definedbyamodifiedandmobilepalatestructure.Allhaveakeeledsternum;referredtoas acarina(meaningkeeled),thoughnotallareabletofly(e.g.,penguins–thoughtheydo“fly”inthe water).Inwhatotherwaysdoesthemorphologyofbirdssuggestthattheyarecapableofflying? Examinethepigeonskeleton.Notethehighlymodifiedforelimb.Whichspecificpartoftheforelimbis themostderived?Howdobirdscompensatefortheirextremelyspecializedforelimb? 10 Mammalia–Mammals Today,placentalmammalsaredominantonalmostalllandmassesexceptAustralia.LiketheAmphibians, wedonothavetimetoexploremammalsinanyrealdetail.Instead,wewillfocusonaparticular mammaliansynapomorphy,uprightlimbposture.Moderninsectivores(e.g.shrewsandtenrecs)are presentdaymammalsthatarethoughttomostresembleancestralmammals.Oneofthebiggest innovationsweseeinmammalsisanuprightposture,placingthelimbsunderneaththetrunk. Comparethemammalianandsalamanderlimbposture.Howaretheysimilar?Howaretheydifferent? 11