Download BIOL 2015 – Evolution and Diversity

BIOL2015–EvolutionandDiversity
Lab11:Ecdysozoa
Introduction
EcdysozoaisagrouporiginallysupportedbyribosomalRNAgenesanditisnowwidelyacceptedasa
monophyleticclade(seeFigure1).Ecdysozoacomprisesthemostdiverseandsuccessfulgroupof
animalsontheplanet.Itincludesnematode,arthropoda,andtardigrada.Ecdysozoaand
LophotrochozoaarethetwolargesubdivisionsthatcomposethecladeProtostomia,agroupthatshares
thesynapomorphyofthemouthdevelopingfromanembryonicstructurecalledtheblastopore.Inturn
ProtostomiabelongstoalargergroupwithinthekingdomAnimaliacalledBilateriabecausethese
animalsarebilaterallysymmetrical.
Allecdysozoansbuildacuticleanouterlayeroforganicmaterialthatfunctionsasanexternalskeleton
(calledexoskeleton).Thecuticleisgenerallynotmineralizedandthismeansthattheskeletoncanbe
builtthinnerandlighterthaninotheranimalsanddoesnotrequireasourceofmineralsforits
construction.Alsoamineralskeletonrequiresjointstoallowflexibilitywhereasanorganiccoveringcan
beflexibleifitisthinenough.
ThenameEcdysozoareferstothefactthatmanymembersofthisgroupregularlyshedtheircuticleina
processcalledecdysis(Greek:ek=out,off+duien=toput).Ecdysisishormonallycontrolledbyaclass
ofsteroidsappropriatelycalledecdysteroids.Ifyouhaveeverseenaninsectcrawloutofitsoldskinora
butterflyleavingitschrysalisthenyouhaveseenecdysistakeplace.Theabilitytoshedthecuticlehas
openedupoptionsforecdysozoansthatarenotavailabletoanimalswithskeletons.Inanimalswitha
mineralizedskeleton,growthcanonlyoccurbyaddingmineraltotheexistingskeletonlimitingthe
animal'sformasitgrows.Whilemanyecdysozoansmaintaintheirbasicbodyformthroughouttheir
entirelife,ecdysisremovesthislimitation.Forexample,manyinsectshavetakenadvantageofthis
processandundergopartialorcompletemetamorphosisbeforereachingtheadultstage.allowingthe
larvatolookcompletelydifferentfromadultand,insome,casesthisallowstheadulttoliveina
completelydifferentenvironmentthanthelarva.
Inbasalanimalsandmanydeuterostomessexualreproductionisaccomplishedbyreleasingmass
quantitiesofgametesintotheenvironmentandleavingfertilizationtochance.Inmostspeciesof
ecdysozoansthespermiseitherdelivereddirectlyintothefemale'sbodyordepositedontotheeggsas
theyarereleased.Thesestrategiesgreatlyincreasethelikelihoodofsuccessfulfertilization.Wewillsee
thatthesesamestrategiesareusedbythevertebratesbuthaveevolvedindependently.
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Trochozoa
Lophophorata
Ecdysozoa
Figure1.AphylogenetictreebasedonDNAdata.Dunnetal.2008.
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Nematoda
Nematodes have a more complex body plan than that of flatworms but simpler than annelids. Freeliving(non-parasitic)nematodesareextremelycommoninmostkindsofhabitatsbuttheyareusually
toosmalltosee.Parasiticnematodesarealsoverycommonand
areoftenmuchlarger.
Nematodefeatures:
• Three tissue layers in embryo.The presence of mesoderm
inadditiontoectodermandendodermisatraitthatisbasal
toallbilaterians.
• Pseudocoelomate:The inside of a nematode's body is
mostly filled with empty space called the pseudocoel. This
spacemightatfirstappeartobethesameasthecoelomin
an earthworm but it isn't. The pseudocoel develops in a
differentwaythanthecoelomofacoelomateand,unlikea
true coelom, there are no mesodermally-derived tissues
and there are no mesodermlly-derived structures
surroundingtheendodermofthedevelopinggut.
• Complete digestive tract:Comparable to that of annelids
but nematodes show little or no specialization of different
gutregions.
Figure2.Ascarisfemaleslide.
• No circulatory system: Nematodes don't have hearts blood
vesselsorblood.Thefluidinthepseudocoelpassivelycirculates
nutrientsandothersubstancesthroughoutthebody.
• Cuticle:a tough flexible acellular layer on the outside of the
body.Becausethecuticleisn'tstretchynematodesmustmoltin
order to grow. Nematodes have this feature in common with
arthropods.
Find the preserved specimens of Ascaris lumbricoides the giant
roundworm of humans on display and find the mouth anus and
laterallineswhichrundownthesidesasveryshallowgroovesinthe
cuticle.Thelaterallinesareasensoryorgan.
Findapreparedslidelabeled"Ascarislumbricoidesesophagus
c.s.".
Noticethecuticle,thelargepseudocoelandthemuscularintestine
(esophagus)inthecenteroftheanimal.Oneachsideofthebody
thehypodermisthickensandprojectsintothebodythelateralline.
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Figure3.Ascarismaleslide.
Eachcordcontainsanexcretorycanal(atleastinthissection)andalateralnervecord.Findthemuscle
tissuethatlinestherestofthebodywallandfindthesmalldorsalandventralnervecords.Nematodes
areuniqueinthatthemusclecellsareindirectcontactwiththenervecords.
Findapreparedslidelabeled"Ascarismale&femalec.s.".
Notethefollowingstructuresonthefemalesection:OvaryandUterus.Onthemalesectionnote
thetestis-alongtubeloopingbackandforththroughoutthebody,incross-sectionthetestisappears
tobemultipletubes.Spermareproducedwithinthetestis.Thevasdeferens(alsocalledductus
deferens)isanotherpartofthesametubularmalereproductivetract;itisresponsibleforstoringsperm.
ComparetoFigures2and3.
Trichinellaspiralis
ThediseasetrichinosisiscausedbyTrichinellaspiralis,whichresultsfromeatingundercookedmeat.
Thecontaminatedmeatcontainsencapsulatedcystsofcontaininglarvae.Thehost'sdigestiveenzymes
breakdowntheprotectivecapsuleofthecystthusreleasingtheenclosedlarva.Itmaturesintoanadult
worminthedigestivetractandformscystsinmuscletissue(amongothers).
Findapreparedslidelabeled"Trichinellaspiralismusclesec."toobserveacyst.
Arthropoda
Thephylumarthropodaisbyfarthemostdiverseofalltheanimalphylaintermsofnumberofspecies
habitatsandwaysofliving.Thereareatleastamillionarthropodspeciesaccountingforover80%of
knownanimalspecies.Arthropodshaveadaptedtomanydifferentenvironments(marinefreshwater
andterrestrial);fewotheranimalphylaareinsuchadiverserangeofplaces.Arthropodshaveanumber
ofdistinctivefeaturesintheirbodyplan:
• Segmentedbodywithspecializedandfusedsegments.Arthropodsareclearlysegmentedandthe
differentsegmentsareverydifferentfromoneanotherinformandfunction.Alsoarthropodbodies
aremadeofseveralgroupsoffusedsegments;thefusedsegmentsarecalledtagmata(singular:
tagma)andtheyactlikeindividualsuper-segments.Eachgroupofarthropodshasacharacteristic
setoftagmata;forexampleinsectshavethreemaintagmatawhilespidershaveonlytwo.Ineach
groupthesesegmentshavetheirownuniquenames.
• Cuticle.Arthropodbodiesarecoveredwithacuticlemadeofchitinforminganexoskeleton.Where
elsehaveweseenchitinousstructuresthissemester?Foreachstructureyoucomeupwithtryto
identifythephylum,class,andorderoftheorganism.Insomearthropods(suchascrabs)the
exoskeletonismademorerigidwithcalciumdeposition.Thefirstarthropodslivedintheocean;
theirexoskeletonsprotectedthemfromattackandprovidedplacesfortheirmusclestoattach.
Whenlatergroupsofarthropodsmovedontothelanditturnedoutthattheexoskeletonhappened
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tobeveryfunctionalinpreventingthebodyfromdryingout.Thisisagoodexampleofhowa
characteristicthatevolvedinoneenvironmentcanbecomeimportantinanorganism’sabilityto
adapttoanotherenvironment.
• Jointedappendages.Mostarthropodshavemultiplejointedlegs,antennae,mouthparts,andother
bodypartsaspartoftheexoskeleton.
• Metamorphosis.Manyanimalscansimplygrowcontinuouslythroughouttheirlives,called
indeterminategrowth.Arthropodshoweverareconfinedintheirrigidcuticle.Inordertogrowthey
mustmolt.Thentheyquicklygrowbigger(byabsorbingwaterorair)beforetheyformanewhard
cuticle.Theirdevelopmentdoesn’talwaysproceedinaseriesofgradualchanges.Instead,they
oftengothroughadistinctmetamorphosisinwhichtheychangetheirbodyformdramaticallyas
theymoltandformanewexoskeleton.Theclassicexampleofthisisthemetamorphosisofa
caterpillarintoabutterfly.
• GasExchange&Osmoregulation.Confinedintheirexoskeletonsarthropodsneedspecialstructures
forgasexchange,osmoregulation,andexcretion.Thesespecializedstructuresalsoseemtocreate
opportunitiesforsomearthropods.Withtheirtrachealsystemforgasexchangeandtheirtubules
forosmoregulation,insectsareabletoliveindryconditionsthatwouldkillmostinvertebrates.
Chelicerata–Spiders,Ticks,Mites,andtheHorseshoeCrab
TheCheliceratesaremostlyterrestrialandalmost
entirelypredatory(exceptmitesandtickswhich
canbeparasitic).Thehaveuniramusappendages
thatiseachappendagecomesoutsinglynotin
pairsasincrustaceans.Theirbodyisdividedinto
twotagmata,theprosoma(alsocalledthe
cephalothorax),andtheopisthosoma(or
abdomen).Thereareover75,000extantspecies
inthesubphylumchelicerata.
Theprosomahas6pairsofappendages:
chelicerae(whichformthemouthparts),
Figure4.Theexternalanatomyofchelicerates.The
pedipalps(whichhavedifferentfunctionsin
bodyisdividedintoacephalothorax(prosoma)andan
differentchelicerategroups),and4pairsof
abdomen(opisthosoma).
walkinglegs.Theyhavenomandiblesor
antennaeandhavesimpleeyes.
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Merostomata
Themerostomataisaclassofmarinechelicerates
commonuntilthegreatPermianextinctionbutwith
only4speciestoday.Theyliveincoastalwatersofthe
EasternUSandinSoutheastAsia.Theyuse
cyanoglobintobindoxygen(containingcopper
insteadofiron)makingtheirbloodblue.Theypreyon
mollusksandpolychaetes.
FindthepreservedspecimensofLimuluspolyphemus
theAtlantichorseshoecrab.Identifythecarapace,
theabdomen,andthetelson(tail).Youshouldbe
abletofindthesimplemedianeyeandlateral
compoundeyes.Notetheunfusedbodysegmentson
theventralsurface.Findthemouth,anus,chelicerae,
andpedipalps.Noticethattheseappendagesarevery
similartothewalkinglegs.Gentlylifttheoperculato
observethegills.
Figure5.ExternalanatomyofHorseshoeCrabs.
Arachnida
Arachnidscomprise98%ofthechelicerates,with
mostbeingwelladaptedtoterrestrialenvironments
andpossessingadaptationsthatenablethemto
feedoninsects.Thisclassincludesspiders,
scorpions,ticks,andmites.Italsoincludes
fascinatinggroupssuchasamblypygids,opiliones,
andpseudoscorpions.Thecheliceraeareoften
modifiedasfangsinthisgroup(Figure6)andmay
beassociatedpoisonglands.Becausetheylackjaws
arachnidscan'tingestsolidfood.Insteadtheysuck
thebodyfluidsfromtheirprey.Inthisclassgaseous
exchangeisaccomplishedwithbooklungs.
Spiders
FindthepreservedspiderTarantulaondisplay.
Carefullyexaminethepreservedtarantulatolocate
thefangs(chelicerae),pedipalps,cephalothorax,
andabdomen.Lookforthesmallsimpleeyes.Also
Figure6.Externalmorphologyofaspider.Observe
examinethelivingtarantula.(Pleasedon'ttryto
thecephalothoraxandtheabdomen(or
removeitfromtheterrarium!)Theselargespiders
opistosoma).
relyheavilyondetectinggroundvibrationsthrough
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theirlegsandbodiestosensepreyandenemies.Manyofthedensehairsontheirbodiesaresensillae
ortactilereceptors.
Scorpions
Findthepreservedscorpionsondisplay(handlethemverycarefully).Scorpionsaredistinguishedbya
subdividedabdomentoproduceatail-likeextensiontippedbyastinger(Figure4).Theirpedipalpsare
modifiedaspincers.Examinetheventralsurfacetofindtheslit-likeopeningsthatleadtothebook
lungsandthefringedsensorystructurescalledpectines.
TicksandMites
Thesearachnidshavecompletelyfusedcephalothoraxesandabdomens.Ticksfeedonvertebrateblood
andmaytransmitdiseasesincludingRockyMountainSpottedFever,Tularemia,andLymeDiseasefrom
animalsrangingfromwhalestobirds.Mitesfeedonvertebrateskinandskinsecretions.
Findapreparedslidelabeled"TickandMite(wm)".
Besureyoucandistinguishbetweenticksandmites(andnotjustonthebasisofsize!).
Crustacea
Crustaceaisaverylargegroupof
arthropods.Itincludescrabs,lobsters,
crayfish,shrimp,krill,andbarnacles
(approximately40,000species).Like
otherarthropodscrustaceanshavean
exoskeleton,whichtheymolttogrow.
Theyaredistinguishedfromother
groupsofarthropodssuchasinsects
myriapodsandcheliceratesbythe
possessionofbiramous(two-parted)
limbs.Theyshowawidedegreeof
morphologicaldiversitythereisnosuch
thingasatypicalcrustacean.The
Figure7.Externalanatomyofacrustacean.
majorityofcrustaceansaremarine,
althoughsomehaveadaptedto
freshwaterenvironmentswithafewbecomingcompletelyterrestrial(pillbugs).
Findthepreservedspecimensofcrayfishondisplay.Findthecephalothoraxandabdomen;5pairsof
walkinglegsthefirstpairenlargedaschelipeds(orpincers);2pairsofantennae(thesecondpair
shorterandbifurcatedaretheantennules);theabdominalappendagesthatarespecializedas
swimmerets.Observetheendopodandexopodregionsoftheseappendages.Carefullylifttheedgeof
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thecarapacetoobservethegillsattachedtoeachofthewalkinglegs(howdoesthisrelatestothe
biramouscondition).Finally,youshouldexaminethetelsonanduropods.Thetelsonisamodifiedbody
segmentandtheuropodsaremodifiedappendages.
Barnacles
Findthepreservedspecimensofgoosebarnacleswehaveondisplay.Thesefilterfeedingcrustaceans
aresessileasadults.Foodistrappedbytheelaboratecirri(orfeedinglegs)whichprojectandwavefrom
thecalcareousshellthattheseanimalssecretearoundthemselves.Barnaclesmatewiththeirsessile
neighborswiththelongest(relativetobodysize)malereproductivestructuresintheanimalkingdom.
Myriapoda
Thesearthropodshavemanyuniramouslegsas
thenamessuggests.Theybreathethrough
spiraclesthatconnecttoatrachealsystem.
Centipedesarenocturnalfastandactive
predators.Theyhaveapairofforcipulesfrom
whichtheyinjectvenomtotheprey.Findthe
preservedcentipedesondisplay.Notethat
mostbodysegmentshaveonlyonepairoflegs.
Millipedesareslowmovingandfeedonplant
materialthathasbeguntodecompose.Findthe
preservedmillipedesondisplay.Notethatmost
bodysegmentshavetwopairsoflegs.
Figure8.AnatomyofMillipedesandcentipedes.
Hexapoda
Withapproximately1.4to1.8millionspeciesand
countingtherearemorespeciesofinsectsthan
allotheranimalgroupscombined.Manymillions
morearelikelytobediscovered.Insectsarekey
playersinthevastmajorityofterrestrial
environments.Theyinventedflyinglongbefore
reptilesandevencultivation(leaf-cuttingants
cultivateafunguswithcollectedleaves)and
farming(manyantspeciesherdaphidsfromplant
toplant).Theyarepollinators,herbivores,
parasites,diseasevectors,andpredators.
Figure9.Insectexternalanatomy.
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ThemostdiversegroupofinsectsistheColeoptera(thebeetles).ForexampleErwinandScott(1980)
foggedtropicaltreesinPanamawithinsecticidesandestimatedthateachtreespecieshas170unique
speciesofbeetlesadaptedtolivingonit.
Insectsuccessprobablycomesfromavarietyoffactors.Theyarewelladaptedtolandbyhavingawaxy
cuticlethatpreventsdesiccation.Theyaretheonlyinvertebratesthatcanfly,whichallowsgreater
dispersion,theabilitytolocatefarawayfoodsourcesand/ormates,andescapefrompredators.Some
insectsaremigratoryliketheMonarchbutterfly.Anotherlikelyreasonfortheirsuccessis
metamorphosis,whichallowstheyoungtospecializeinfeeding(forexamplethelarvaeofbutterflies)
whileadultsareusuallyspecializedfordispersionandreproduction.Canyouthinkofanyother
explanationfortheirsuccess?
Theinsectbodyhasthreepartsthehead
thethorax(withthreeleg-bearing
segments)andtheabdomen.Thehead
hasantennaeamouthwithmandiblesand
compoundeyes.
Findthepreservedlubbergrasshoppers.
Locatethethreeregionsofthebody;the
head,thorax,andabdomen(Figure10).
Ontheheadfindthelargecompound
eyesandtheantennae.Findthelabrum
andliftittoobservethemandiblesand
thetwopairsofmaxillaewithpalps
(Figure11).Onthethoraxfindthethree
subdivisionsthateachbearasetofwalkinglegs.
Figure11.Grasshopperexternalanatomy.
Noticethatthetwopairsofwingsalso
originatefromthethorax.Each
abdominalsegmenthasapairofopenings
calledspiracles,whichadmitairtothe
trachealsystem.
Findtheinsectcollectionsondisplay.
Observethedegreeofdiversitybodysize
changesinstructureandsoforth.
Figure10.Mouthpartsofagrasshopper.
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Tardigrada
Usuallytardigradesare1millimeter(0.039in)long
whentheyarefullygrown.Theyareshortand
plumpwith4pairsoflegseachwith4-8clawsalso
knownasdisks.Tardigradesareprevalentinmoss
andlichen.Technicallytheyarenotextremophiles
becausetheydonotpossessstructuresthatare
specificallyadaptedtoanextremeenvironments,
theyaresimplyabletowithstandmanyextreme
environments(desiccation,heat,cold,pressure,
etc…).Forexample,theycansurvivetemperatures
of-272°C(oneaboveabsolutezero)forafew
minutes.Theycansurvivethevacuumofspaceand
pressuresofupto1200atmosphereswhichisthe
pressureofwaterat36,000feet(thesamepressure
Figure12.Ascanningelectronmicrographofawaterbear.
atthebottomofoceantrenches).Mostare
phytophagous(planteaters).Beabletoidentifya
waterbear.
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