英语（英文）版动物世界（动物介绍）introductiontoanimals

IntroductiontoAnimalsCharacteristicsMulticellularOrganizationHeterotrophicSexualreproductionanddevelopmentMovementAnimalClassesAnanimalclassismadeupofanimalsthatareallalikeinimportantways.Scientistshavegroupedanimalsintoclassestomakeiteasiertostudythem.Therearemanydifferentanimalclassesandeveryanimalintheworldbelongstooneofthem.Thefivemostwellknownclassesofvertebrates(animalswithbackbones)aremammals,birds,fish,reptiles,amphibians.Theyareallpartofthephylumchordata--Irememberchordotabythinkingofspinalchord.Therearealsoalotofanimalswithoutbackbones.Thesearecalledinvertebratesandarepartofthephylumarthropoda(arthropods).Twoofthemostcommonlyknownclassesinthisphylumarearachnids(spiders)andinsects.www.kidzone.ws/animals/MammalsPeoplearemammals.Soaredogs,cats,horses,duckbillplatypuses,kangaroos,dolphinsandwhales.Whatdoalltheseanimalshaveincommon,youask?Theansweris–MILK!Ifananimaldrinksmilkwhenitisababyandhashaironitsbody,itbelongstothemammalclassMammalsareoneofthe6mainclassesofanimals.Animalclassesaregroupsofanimalsthatscientistsconsidertobealikeinsomeimportantways.Mammalsaretheanimalclassthatpeoplebelongto.Thereareonlyabout4,000kindsofmammals.Warm-bloodedBirdsBirdsareanimalsthathavefeathersandthatarebornoutofhard-shelledeggs.Somepeoplethinkthatwhatmakesananimalabirdisitswings.Batshavewings.Flieshavewings.Batsandfliesarenotbirds.Sowhatmakesananimalabird?Theanswerisfeathers!Allbirdshavefeathersandbirdsaretheonlyanimalsthatdo.Thefeathersonabird’swingsandtailoverlap.Becausetheyoverlap,thefeatherscatchandholdtheair.Thishelpsthebirdtofly,steeritselfandland.FishFisharevertebratesthatliveinwaterandhavegills,scalesandfinsontheirbody.Therearealotofdifferentfishandmanyofthemlookveryoddindeed.Thereareblindfish,fishwithnoseslikeelephants,fishthatshootdownpassingbugswithastreamofwaterandevenfishthatcrawlontolandandhopabout!ReptilesReptilesareaclassofanimalwithscalyskin.Theyarecoldbloodedandarebornonland.Snakes,lizards,crocodiles,alligatorsandturtlesallbelongtothereptileclass.AmphibiansAmphibiansareborninthewater.Whentheyareborn,theybreathwithgillslikeafish.Butwhentheygrowup,theydeveloplungsandcanliveonland.ArthropodsArthropodsisahugephylumofanimals--itincludeselevenanimalclasses:Merostomata,Pycnogonida,Arachnida,Remipedia,Cephalocarida,Branchiopoda,Maxillopoda,Malacostraca,Chilopoda,Diplopoda,andInsecta.Anyanimalsthathavemorethanfour,jointedlegsarearthropods.Insects,spidersandcrustaceansallbelongtothisclassofanimals.ZoologistArachnologistCarcinologistConchologistEntomologistHerptologistIchthyologistMalacologistMammalogistOrnithologistPaleozoologistMarinebiologistbotanistMulticellularOrganizationMostanimalscontainlargenumbersofcells.Humanscontain50trillioncells.Inmostanimals,thereisadivisionoflabor.Specializationistheadaptationofacellforaparticularfunction.Tissuesaretheorganizationofcells.Cellareabletoorganizebythejoiningofcellsbycelljunctions.Cellspecializationhasallowedorganismstoevolveandadapttomanyenvironments.AnimalsareHeterotrophicTheymustobtaincomplexorganicmaterialfromothersources.Mostaccomplishthisthroughingestion.Digestionisaccomplishedwithintheanimal.Thisprocessextractsthecarbohydrates,proteinandlipidsfromthefoodeaten.SexualReproductionandDevelopmentSexualreproductionrestoresthediploidnumberandincreasesgeneticvariation.Duringthedevelopmentalprocess,thezygoteundergoesmanymitoticdivisions.Theseidenticalcellsmustundergodifferentiation.Differentiationisprocessofcellbecomingdifferentfromeachotherandbeingspecialized.MovementMostanimalareabletomove.Theabilitytomoveresultsfromtheinterrelationsoftwotypesoftissuesfoundonlyinanimals:nervoustissueandmusculartissue.Thereareafewanimalsthataresessile.OriginandClassificationThefirstanimalsprobablyarosefromthesea.Taxonomistshavegroupedanimalsintoseveralphylabasedonevolutionaryrelationships.Manytaxonomistrecognize30ormoreanimalphyla.Wewillinvestigate11phyla.TenofthephylaincludeinvertebratesandonlyChordataincludesthevertebrates.AnimalBodyStructureSymmetryGermlayersBodyCavitiesSymmetryAsymmetryreferstotheconsistentoverallpatternofstructureofananimal.Animalshavethreepatternsofsymmetry.Asymmetry–nosymmetryRadialSymmetry–similarpartsbranchinalldirectionsfromacentralpointBilateralSymmetry-similarhalvesoneithersideofacentralplane.PatternsofSymmetryIdentifytheTypeofSymmetryMostanimalshaveadorsal,ventral,anteriorandposteriorsideororientation.Dorsal–topVentral–bottomAnterior–headPosterior-tailMostanimalsexhibitcephalization,theconcentrationofsensoryandbrainstructuresintheanterior.Animalswithcephalizationhaveahead!GermLayersGermlayersarefundamentaltissuetypesfoundinallanimalsexceptsponges(notruetissues).EctodermMesodermEndodermBodyCavitiesMostanimalshaveafluidfilledspacethatformsbetweenthedigestivetractandtheouterwallofthebodyduringdevelopment.ThisspaceisknownasaCOELOM.Acoelomate(withoutacoelom)2germlayersectodermandendodermnotseparatedbyacavityleastcomplexbodyplanspongesandcnidarians3layeracoelomate3germlayersendoder