TURTLEDISSECTIONLABTurtleshavehadover200millionyearstoevolveandhaveoutlivedthedinosaurstobecomeoneoftheOLDESTLIVINGfamiliesintheanimalkingdom.TheorderCHELONIAconsistsofabout250speciesofturtlesandtortoises.Thetermtortoiseisgenerallyreservedforlanddwellers,whileturtlereferstocheloniansthatliveinwater.INTEGUMENT&STRUCTURE:Becauseamphibiansexchangegasesthroughtheirskin,itmustbemoistandthinenoughtoallowrapiddiffusion.Oneofthedrawbacksofthiskindofskinisthelossofbodywaterthroughevaporation.Thethick,dry,scalyskinofreptilesisanimprovement,becauseitiswatertight.Thetoughskinofareptilehelpstoconservewaterandprotectstheanimalagainstinfections,injuries,andthewearandtearassociatedwithlivingonland.SurfacecellsfillwithKERATIN,thesameproteinthatformsyourfingernailsandhairandbirdfeathers.Lipidsandproteinsintheskinkeepitwatertight. Lookattheturtle’sshells.Aturtle’sprotectiveshellis

formedfromthefusionofbonesfromtheribsandvertebrae.Thespineandribsareattachedtotheshell,soturtlescan’treallycrawloutoftheirshellslikeinthecartoons.

ThebonesoftheshellaredividedintosectionscalledSCUTES,andarecoveredwithskincontainingaproteincalledKERATIN.Scuteshavenerveendings,soaturtlecanfeelsomethingtouchingitsshell.Thescutesandtheboneunderneathcangrowallowingtheturtletoexpandandgetlarger.Turtlescanregeneratedamagedscutes,andsomescuteshaveringssimilartogrowthringsontreesthatcanbeusedtoestimateage.TheBRIDGEalongthesidesconnectstheCARAPACE(dorsalshell)tothePLASTRON(ventralshell).

Reptileshaveanunusualstancenotseeninotheranimalgroups.Theirlimbsprotrudeatrightanglesfromtheirbodies. Inallotheranimalswitharmsandlegs,theshouldersandpelvicbonesareOUTSIDETHERIBCAGE.InturtlestheskeletonismodifiedsotheLIMBGIRDLES(shouldersandpelvis)arelocatedINSIDETHERIBCAGE.Thisallowstheturtletopullitslimbsinsideitsshell.

TEMPERATUREREGULATION:ReptilesareECTOTHERMIC,commonlycalled“coldblooded”.Theydon’tmaketheirownbodyheat.Theymaintaintheirbodytemperature(THERMOREGULATION)byabsorbingheatfromtheirenvironment.Whenitgetstoowarmtheyfindacool,shadyspot.Whentheygettoocool,theywarmthemselvesbybaskinginthesun.ADVANTAGESOFBEINGECTOTHERMIC:

(1) ECTOTHERMSrequireverylittleenergybecausetheirmetabolismissolow.(2) Becausetheirmetabolismissoslow,ectothermscansurviveonabout1/10theamountoffood

neededbythesamesizeendotherm(warmbloodedorganism).DISADVANTAGESOFBEINGECTOTHERMIC:

1) EctothermscanrunorswimatMAXIMUMSPEEDFORONLYSHORTPERIODSoftime.(Theirmetabolismcan’tprovideenoughenergytokeepthemgoinglonger.)

2).EctothermsCAN’TLIVEINVERYCOLDCLIMATES.Theysurviveinmoderateclimatesonlybybecomingdormant(HIBERNATING)duringthecoldestmonths.

Becausetheirbodytemperatureisdependantonthetemperatureoftheirenvironment,reptilesareabundantinthewarmerregionsoftheworld,afewliveincolderpartsofthetemperatezone,butnoneliveintheArcticorAntarcticregions.

EXTERNALFEATURES:(1) Locatetheexitopeningbelowtheturtle’stail.Likeamphibians,theCLOACA,amultipurposecavitysharedbythe

digestive,reproductive,andexcretorysystemsexitsthroughaVENT.(2) Lookatthefeetoftheturtle.Oneofthecharacteristicsyousawinamphibians

(mudpuppy)wasfeetwithNOCLAWS.NoticetheCLAWEDFEETinreptiles.Manyreptileshavefeetwithclaws,butremembersomelikesnakesdonot.

(3) Lookattheeyes.Likefrogs,turtleshaveaNICTITATINGMEMBRANEthatactsasathirdeyelidtocoverandprotecttheeyeballunderwater.

(4) Lookbehindtheeyesforthe“ears”.TheTYMPANIC

MEMBRANE(eardrum)isdirectlybehindtheeyes.Turtleshaveverypoorhearing.

(5) Lookatthenose.TheEXTERNALNARES(nostrils)connectinsidetothemouthjustlikeinamphibians.Two

INTERNALNARES(connecttoEXTERNALNARESoutside)whichallowtheturtletobreathewithitsmouthclosed.

(6) Openthemouth.Unlikeotherreptiles,turtleshaveNOTEETH.InsteadtheyhaveasharpBEAKmadeofKERATIN.Themouthinaturtleisverysimilartothatseeninamphibians.TheGLOTTIS,averticalslitjustbehindtheTONGUE,istheopeningtotherespiratorysystem.BehindtheglottisistheGULLET(theopeningintothedigestivesystem).

Whatsexisit?Maleturtleshavelongerfrontclawsandalongertail.Theventinmalesisfartherbackfromtheedgeoftheirshellthaninfemales.Theirplastronisslightlyconcavetoallowformalestoclimbontopoffemalesduringmating.Theplastroninafemaleisslightlyconvextoallowmoreroomforeggsinside.

INTERNALDISSECTIONINSTRUCTIONS:REMOVEyourPLASTRON:Examinethecarapaceandtheplastronoftheshell.Theplastronwillhavetoberemovedinthemountedskeleton.Removingtheshellisaverydifficultandtimeconsumingprocedure.Itwillgiveyouanappreciationofthearmorthatprotectstheturtlefrommostpredatorsandwhichpartiallyaccountsforthelonglivesthatturtleslive.GoslowandBECAREFUL!Besureandnotinjureyourselforyourlabpartnerwhileremovingtheshell.DONOTUSEYOURSCALPELTOPRYOPENTHESHELL...itwillbreak.Usethesawandthebonecutterstoremovetheplastron.Thereisonly2sawstosharefortheentireclasssobepatient.Disconnecttheskinaroundthelegstoseparateitfromtheshell.Thisisadifficultandtimeconsumingprocedure!Itwillgiveyouanappreciationforthearmorthatprotectstheturtlefrommostpredatorsandwhichpartiallyaccountsforthelonglivesthatturtleslive.Manytoughmembranesalsoattachthecarapaceandplastronandthesemembranesneedtobecutwitharazorbladeorscalpel.Aftertheseincisionshavebeenmade,youshouldbeabletocompletelyremovetheplastronandalloftheinternalorgansshouldbevisibleinthecarapace.ReptilesareEUCOELOMATES.Thespaceyouseesurroundingtheinternalorgansis“truecoelom”(bodycavitylinedonbothsidesbymesoderm).TheyellowishstructuresarestoredFAT.Turtlesdonotstorefatinthesamewayasfrogsdo.FatstoresarereservoirsforfoodusedduringHIBERNATION.TheMESENTERY(fan-likemembrane)connectstheinternalorgansjustlikeinafrog.

DIGESTIVE:(1) Justlikeinafrog,foodmovesfromPHARYNX(backofthroat)downtheGULLETintotheESOPHAGUS

totheSTOMACH.Acidsecretedbythewallsofthestomachandthestomachmusclesworktobreakdownfood.TheesophagusisamuscularstructureBEHINDtheTRACHEAwhichisthe“windpipe”forthetruelungbreathers.Makesureyoucanlocatealltheseboldterms.

(2) ThePYLORICSPHINCTERmuscleattheendofthestomachcontrolsthepassingofdigestedfoodinto

theSMALLINTESTINE.Atthebottomofthestomachyouwillseeapinchinglikeanarrowingthisisthepyloricsphincter.Makesureyoucanlocatethetermsinbold.

(3) TheupperportionoftheSMALLINTESTINEclosesttothestomachistheDUODENUM.ThenextcoiledsectionistheILEUM.Afan-likemembranecalledtheMESENTERYholdsthefoldsofthesmallintestinetogether.Thesmallintestinereceivesbilefromtheliverandpancreaticenzymes(includingtrypsin)fromthepancreas.Digestioniscompletedhereandnutrientsareabsorbedthroughthevilli(smallfingerlikeextensions)liningthesmallintestine.Makesureyoucanlocatethetermsinbold.

(4) ThelowerendofthesmallintestineleadsintotheLARGEINTESTINE(alsocalledtheCOLON),whereundigestedwasteiscollectedandpassedintotheCLOACA,amultipurposecavity.Makesureyoucanlocatethetermsinbold.

(5) Digestivewaste,nitrogenwastefromtheKIDNEYS’S(urine),aswellaseggsandspermallpassthroughtheCLOACAontheirwayoutofthebodythroughtheVENT.Makesureyoucanlocatethetermsinbold.

(6) LocatetheLIVER.ThemainfunctionsofthelobedLIVERaretoMAKEBILE,STOREGLYCOGENandVITAMINS,andPROCESSTOXINSincludingNITROGENWASTEforthekidneystoremove.

(7) LocatetheGALLBLADDER,agreenishcoloredsacfoundintheliver,storesBILEmadebytheLIVER.

(8) LocatethePANCREASisanelongatedorganlocatedinthefirstloopofintestinebetweenthebeginningofthesmallintestineandstomach.ItsecretesTRYPSINthatisusedinthesmallintestinetobreakdownproteins.

RESPIRATION:(1) TurtlesuseLUNGSforrespiration.AirenterstheGLOTTIS,movesdowntheTRACHEA(atubelinedwith

cartilageringswhichhelptoholdtheairwayopen)whichsplitsintotwoBRONCHIthatcarryairintothelungs.Unlikeafrogwhoselungsweresimplesacs,thelungsinaturtlehavemanysmallindividualairsacscalledALVEOLI(sing.ALVEOLUS)toincreasesurfaceareaforgreatergasexchange.Someseaturtlescanexchangegasesthroughtheskinoftheircloaca.

CIRCULATORY:Likeamphibians,thecirculatorysysteminreptilesconsistsofaCLOSEDTWOLOOPSYSTEMandaTHREECHAMBERHEARTsurroundedbyaPERICARDIALMEMBRANE.(1) LocatetheRIGHTATRIUM,LEFTATRIUM,andVENTRICLE.LookfortheSINUSVENOSUSandCONUS

ARTERIOSUS.TheCONUSARTERIOSUSformsthebaseofthe3largearteriesleavingtheheart.

ThePULMONARYCIRCULATIONcarriesdeoxygenatedbloodfromthehearttothelungs,thenreturnsoxygenatedbloodtotheheart.TheSYSTEMICCIRCULATIONcarriesoxygenatedbloodfromthehearttothemusclesandbodyorgansandbringsdeoxygenatedbloodbacktotheheart.RememberaddingasecondloophastheadvantagesofFASTERBLOODFLOWtothebodyorgansandMOREEFFICIENTdeliveryofoxygen.

LowoxygenbloodreturningfromthebodyenterstheSINUSVENOSUS.FromthereitenterstheRIGHTATRIUM.AtthesametimehighoxygenbloodreturningfromthelungsenterstheLEFTATRIUM.Whentheatriacontract,bothkindsofbloodaresenttotheVENTRICLE.Theturtleheartisdifferentfromthatseeninfrogs.InmostreptilesaPARTIALSEPTUMappearstoseparatetheventricletofurtherpreventmixingtotheHIGHandLOWoxygenbloodthatsharesthispumpingchamber.(InCrocodiliansthisseptumdivideriscompletemakingcrocodilianstheonlyreptileswitha4chamberheart.)Whentheventriclecontracts,bothkindsofbloodpassthroughtheCONUSARTERIOSUS,whichhasavalvetopreventmixingofhighandlowoxygenblood.Largearteriesthencarrythehighoxygenbloodouttothebodyorgansandmusclesandlowoxygenbloodissenttothelungstopickupoxygen.**Thereptilecirculatorysystemhasaflexibilitythatamphibians,birds,andmammalsdonot.Pumpingbloodthroughthelungsrequiresenergy.Undersomecircumstancesitisadvantageousforareptiletodivertbloodawayfromthelungs

toconserveenergy.Therearetimeswhenareptilemaywanttosaveenergybybypassingthelungs 1.whenitisinactive(maygoalongtimewithoutbreathing) 2.whenholdingbreathunderwater 3.whentheywanttowarmupfastByconstrictingthebloodflowtothepulmonaryarteries,areptilecanredirectbloodtothebodyandbypass(SKIP)thelungstosaveenergy.Bypassingthelungscanalsohelpareptileraiseitsbodytemperaturequicklybecausewarmbloodfromtheskincanbedirectedtotheorgansdeepinside.EXCRETORYTheexcretorysystemofreptileshelpsthemtoconservebodywater.Snakes,lizards,andotherlanddwellingreptilesexcretenitrogenwasteintheformofURICACID.Unlikeamphibiansthatexcreteurea,uricacidismustlesstoxic(poisonous)soitrequireslittlewaterfordilution.Reptilesloseonlysmallamountsofwaterintheirurine.(1) LocatetheKIDNEYS.Theylieoneithersideofthespineagainstthedorsalbodywall,aretheprimary

excretoryorgans.ThekidneysfilterNITROGENWASTES(URICACID)fromtheblood,anddiluteitwithwatertomakeURINE.ThekidneysalsoREGULATETHEION/WATERBALANCEinthebloodandtissues.

(2) TheURINARYBLADDERisatransparentsacnearthecloacawhichstoresurineuntilitisreleasedthroughtheVENT.UrineflowsfromthekidneysthroughurinaryductstotheCLOACA.

REPRODUCTIONFertilizationinturtlesisINTERNAL.ThereproductivepatternseeninturtlesandtortoisesisOVIPARITY.Thefemalescoopsoutaholewithherhindlegs,depositstheeggs,andcoversthenest.Mostspeciesof

reptilesprovidenocarefortheireggsoryoung.Marineturtlesoftenmigratelongdistancestolaytheireggsonthesamebeachwheretheyhatched.Reptiles,includingturtles,havedirectdevelopment.Babyturtleshatchfromtheireggslookinglikeminiatureadults.Females:AfemaleturtlehaspairedOVARIESthatproducetheeggs,whichpassthroughtheOVIDUCTS,andpassedoutviatheCLOACAthroughtheVENT.Thefemale’sreproductivetractencloseseachegginatoughprotectiveshellasitpassesthroughtheOVIDUCTS.Males:MaleshaveTESTESthatmakethespermwhichpassesthroughtubulescalledVASDEFERENStotheCLOACAandoutofthebody.MaleshaveaPENIStodepositthesperminsidethefemale’sbodywhichincreasesthechancesoffertilization.Inmostorganisms,anindividual’ssexisdeterminedbythepresenceofXorYchromosomes.InhumansXXmakesyouafemale,Xymakesyouamale.Inmanyreptiles,sexisdeterminedbythetemperatureatwhichtheeggisincubated.LocationOFthenest(shadyorinthesun)andlocationINthenest(bottomortop)determineswhetherthebabyturtlewillbeaboyorgirl.Somestudiessuggestthatfemalereptilesmayputtheirnestsindifferentplacesdependingonthemale:femaleratiointhepopulation.TurtleslayAMNIOTICEGGSwith4specializedmembranes,whichsurroundtheembryoinaself-containedaquaticenvironment.Thetoughshellontheoutsideprovidesmoreprotectiontotheembryoinsidethanthejellycoatingofanamphibianegg.TheAMNIOTICEGGisanadvancementthatallowedreptilestomoveoutontolandandnothavetoreturntowatertolaytheireggs.

Thediagramaboveshowstheinternalstructureofsuchanegg.TheeggisnamedfortheAMNIONthethinmembranethatenclosesthedevelopingembryoandthefluidthatsurroundsit;TheYOLKSACenclosestheyolk,afat-richfoodsourceforthegrowingembryo;TheALLANTOISstoresnitrogenwasteproducedbythegrowingembryoANDexchangesgaseswiththeenvironment;TheCHORIONsurroundsalltheothermembranesandhelpsprotectthedevelopingembryo.ProteinandwaterneededbytheembryoarecontainedintheALBUMEN. Theamnioticeggfirstevolvedinreptilesbutalsooccursinbirdsandafewmammals(liketheplatypus).Scientistsbelievethisisevidencethatreptiles,birds,andmammalsevolvedfromacommonancestor.