Proc..Embryol.Soc.Jpn.４３,３–２２(２００９) HEXAPODPHYLOGENY:ACRITICALREVIEW ３ 違２００９ArthropodanEmbryologicalSocietyofJapan ISSN１３４１–１５２７

A CriticalReview ofCurrentDataandHypotheses onHexapodPhylogeny＊

Klaus-DieterKLASS

MuseumofZoology,SenckenbergNaturalHistoryCollectionsDresden,KönigsbrückerLandstraße１５９,０１１０９ Dresden,Germany E-mail:[email protected]

Abstract Themostproblematicfieldsinthereconstructionofhexapodphylogenyare(１)theverybasalsplittingevents amongCollembola,Protura,Diplura,andInsecta(=Ectognatha);(２)thebasalrelationshipsinDicondylia,concerningthe positionofTricholepidionwithrespecttoZygentomas.str.andPterygotaaswellasthemonophylyofZygentomas.str.; (３)therelationshipsamongthethreemajorpterygotanlineagesEphemeroptera,Odonata,andNeoptera;and(４)the largebasalpolytomyinNeoptera,whichincludesPlecoptera,Orthoptera,,Notoptera(=Grylloblattodea), Mantophasmatodea,Embioptera,Dermaptera,,Zoraptera,Acercaria,andEndopterygota(=Holometabola). Thegreatamountofnewmorphologicalandmoleculardataaccumulatedduringrecentyearshassofarnotprovided convincingclarificationofanyoftheabovementionedissues;inconsistencebetweendifferentcharactersandanalyseshas growninproportiontothedata,andthisisalsoreflectedinthenumerousincongruentphylogenetichypothesesthathave beenproposed.Furthermore,theuncertaintyaboutwhichothersubgroupofMandibulataisphylogeneticallyclosestto (MyriapodaorCrustacea,orsomesubgroupthereof)andtheadditionaloptionofhexapodnon-monophyly renderworkonbasalhexapodphylogenyalaborioustaskthatshouldbeembeddedinbroaderstudiesofmandibulatan phylogeny.Thispaperprovidesacriticalreview ofpreviouslysuggestedmorphologicalautapomorphiesofputative hexapodclades,andresultsofrecentmorphology-basedandmolecular-basedcladisticanalysesareembeddedinthese discussions.

Keywords: Hexapoda,Insecta,,,characters,cladistics,morphology,phylogeny

１.Introduction theHexapoda,theDicondylia,thePterygota,andthe Muchofourcurrentconceptsonthephylogenyof Neopteraappearasthemostsevereproblemsinthe HexapodaisbasedontheworksofHennig(１９６９,１９８１), reconstructionofhexapodphylogeny.Onewouldask Boudreaux(１９７９),andKristensen(１９７５,１９８１,１９９１, whethersome substantialprogresshasbeenachieved １９９５,１９９８).AccordingtoKristensen(１９９１:Fig.５),the afterKristensen’s(１９９１,１９９５,１９９８)papers. HexapodacanbedividedintotheCollembola,Protura, Recent years have seen a large number of Diplura,andInsecta(=Ectognatha).InInsectaabasal new contributions relevant to phylogenetic work splitbetweenArchaeognathaandDicondyliaisproposed. in Hexapoda.Many morphologicalpapers focus on TheDicondyliaincludethePterygota,theZygentoma, particularcharactersystems such asthecirculatory andtheisolatedspeciesTricholepidiongertschi(formally system (e.g.,Pass,１９９１,１９９８,２０００;Gereben-Krenn placedinZygentoma).ThePterygotafallintothethree andPass,１９９９,２０００;Passetal.,２００６),ovarioles(e.g., lineagesEphemeroptera,Odonata,and Neoptera.In Büning,１９９４,１９９８,２００６),spermatozoa(e.g.,Jamieson Neoptera, which comprise the vast majority of etal.,１９９９;Dallaietal.,２００１,２００２,２００３,２００４),wings hexapodspecies,１１principallineagesareplacedinan andtheirarticulation(e.g.,Kukalová-Peck,２００８;Haas unresolved basalpolytomy:Plecoptera,Embioptera, andKukalová-Peck,２００１;Béthoux,２００５;Hörnsche- Orthoptera (=Saltatoria), Dermaptera, Dictyoptera, meyerand Willkommen,２００７;Willkommen,２００８), Mantophasmatodea(describedinKlassetal.,２００２), tarsalandpretarsalattachmentdevices(e.g.,Gorb,ed. Phasmatodea,Notoptera(=Grylloblattodea),Zoraptera, ２００４),female genitalia(Klass,１９９８c,２００１a,２００３a, Acercaria (hemipteroid orders),and Endopterygota ２００８;Klassetal.,２００３),mid-abdominalmusculatureand (=Holometabola).Accordingly,thebasalrelationshipsof nervoussystem (Klass,１９９９,２０００;KlugandBradler,

＊ Contributiontothesymposium“ReconstructionofHexapodPhylogeny:AnOverviewfromComparativeReproductiveBiology.”The４３rdAnnualMeetingof theArthropodanEmbryologicalSocietyofJapan,July５,２００７(Sugadaira,Japan). ４ K.-D.KLASS

２００６;KlugandKlass,２００７),visualsystem (Paulus, poorrecordofHexapodafromtheLowerCarboniferous ２０００;Friedrich etal.,２００６),head apodemes and andDevonianaremajorproblems.Morphologicaland mandibulararticulations(Staniczek,２０００;Fürstvon cladisticworkontheearliestknownPterygotafromthe Lieven,２０００;Koch,２０００a,b,２００１),proventriculus UpperCarboniferous is mostrelevantin terms of (Klass,１９９８a,b),orembryonicdevelopment(e.g.,Ikeda order-levelphylogeny.Mostnotably,therehasbeen andMachida,１９９８,２００１;MachidaandAndo,１９９８; substantialprogressrecentlywithregardtothehuge Machidaetal.,２００２,２００４;Machida,２００６).These basal-neopteranassemblageof“”(e.g., contributionssubstantiallyimprovedtheknowledgeon BéthouxandNel,２００２,２００４,２００５;Béthouxetal.,２００４ thecharactersystems inquestionandpartlyledto on“orthopteroid”taxa)andtotheOdonata(Bechly,１９９５, completelynewevolutionaryinterpretations.Extensive １９９６,２００５).Inbothcasespterygotanlineagescouldbe phylogeneticallybasedreviewsonhexapodrelationships tracedbacktotheirearlyrootsatthebeginningofthe were published by Willmann (２００３,２００５a),Beutel UpperCarboniferous.Someotheroutstandingfindings (２００４),and Grimaldiand Engel(２００５),partly also on fossils are highly disputed.One case is the includingthefossilevidence.Otherauthorsusedmuch interpretation of the marine arthropod oftheavailablemorphologicaldataforcladisticanalyses Devonohexapodusasastemgrouphexapodan(Haasetal., eitherincludingallhexapodorders(BeutelandGorb, ２００３;Haas,２００５vs.Willmann,２００５b).Anothercaseis ２００１,２００６)orfocussingonthebasalsplitsinHexapoda the descriptions ofCarboniferous hexapods by J. (BitschandBitsch,１９９８,２０００,２００４).Ontheotherhand, Kukalová-Peck(e.g.,Kukalová-Peck,１９８７,１９９０,１９９１, morphologicalmatricesusedinthecombinedanalysesof １９９２),whichsuggestthatearlyhexapodsfrom various Whitingetal.(１９９７),Wheeleretal.(２００１),Giribetetal. lineagespossessedmanyelementsabsentinallextant (２００４),TerryandWhiting(２００５),andKjeretal.(２００６) relatives(additionalpodomeresinthelimbsofhead, sufferfrommanyshortcomingsthatrendertheirresults thorax,andabdomen;basalpodomeresbearingmultiple spurious. exitesandendites). Onthemolecularsidearichspectrum ofmethods Despite allthese new data,however,hardly forsequencealignment,dataselection,treeconstruc- any substantialprogress has been achieved in the tion,andestimationofcladesupporthasbeendeveloped clarificationofthemostproblematicnodesmentioned inrecentyears.Accordingly,however,therehasalso above;instead,conflictshavegrowninproportiontothe beenincreasingdisputeaboutwhicharethe“right” amountofdata,andnumerousincongruenthypotheses methods. This is an important aspect, because are now on the market.The presentcontribution phylogeneticresultsdrawnfrom adatabasecandiffer surveys the current state of knowledge on the stronglydependingonthemethodsapplied.Thestudies phylogenyofHexapoda,focusedonthebasalsplitsin byWhitingetal.(１９９７),Wheeleretal.(２００１),Kjer Hexapoda,Insecta,Pterygota,andNeoptera.Morpho- (２００４),TerryandWhiting(２００５),andKjeretal.(２００６) logical characters are listed that yield potential are relevantfororder-levelrelationshipsthroughout synapomorphiesofclades(numberedsequentiallyin Hexapoda.Carapellietal.(２０００),Regieretal.(２００４), boldprint),andtheresultsofthevariousanalysesof Giribetetal.(２００４),andLuanetal.(２００５)focusonthe morphological, molecular, and combined data are basalsplitsin Hexapoda.Some furtherpapersare compared.Inaddition,thecurrentevidenceregarding relevantfor the position ofHexapoda within the the(non-)monophylyofHexapodaisbrieflyreviewed. Arthropoda:RegierandShultz(１９９７,１９９８),Shultzand Regier(２０００),GiribetandRibera(２０００),Giribetetal. ２.MonophylyandrelationshipsofHexapoda (２００１),Cooketal.(２００１,２００５),Nardietal.(２００３a,b), RelationshipsofHexapoda Pisanietal.(２００４),Regieretal.(２００４,２００５),Carapelliet Traditionallythemyriapodsorasubgroupofthese al.(２００５),andMallattandGiribet(２００６)(seealso (ProgoneataorSymphyla)wereconsideredthesister Delsuc etal.,２００３).Apartfrom DNA sequences, groupofHexapoda(TracheataorAteloceratahypothe- mitochondrial gene order has been tested for sis).Thecompletelackofsecondantennae(limbless itsphylogenticinformativeness(with datacurrently “intercalary segment”)unambiguously supports this availableforca.１００hexapodspecies),butduetothelack hypothesis,asdoesthetrachealsystem,whichshows ofvariationitcannow beconsideredveryunlikelyto complexsimilaritiesinthemusculatureandinnervation yield evidence on interordinalhexapod relationships ofthespiraclesbetween,atleast,InsectaandChilopoda (Cameronetal.,２００６a,b).Minordifferencesinthe (Klass and Kristensen,２００１). The presence of geneticcodeareprobablyneitherinformativedueto temporalorgans (=Tömösváry’s organs) does not strong homoplasy among subgroups of Hexapoda supportTracheata,becausesimilarorgansoccuramong (Abascaletal.,２００６). crustaceans(KlassandKristensen,２００１:２７０).Thecase Regardingthefossilevidence,thestillwidespread is similar with the tentorialarms,because head non-phylogeneticreasoningaswellastheextremely apodemes resembling the anterior and posterior HEXAPODPHYLOGENY:ACRITICALREVIEW ５

tentorialarms ofHexapodaarealsofoundinmany fusedwitheusterniteintoacoxosternite).Consequently, Malacostraca(e.g.,Marvillet,１９７８,１９８２;Coleman, at most a moderate reduction of the abdominal ２００２). appendages can perhaps be viewed as a hexapod Duringthelasttwodecadesmorphologicalevidence autapomorphy.ComparingHexapodawithMalacostraca accumulated that suggests a close relationship of leadstoadifferentresult.ThepleonofMalacostracaalso HexapodatoCrustacea(TetraconataorPancrustacea representsaposteriortrunktagmawithmodifiedand hypothesis;surveyin Richter,２００２).Onecharacter moreorlessreducedappendages,andhomologising system takentosupportthisview wasthecellular trunk tagmatisation in Malacostraca and Hexapoda compositionoftheommatidia(e.g.,Dohle,２００１),but appearstempting.Anevolutionaryshiftoftheborder thishasbecomeambiguouswiththediscoveryofsome betweenthetwotagmatahasthentobeassumed– ofthecrucialstructuraldetailsinascutigeromorph surelyaplausibletransformation.Forthisissuethe chilopod (Müller etal.,２００３).Severalcharacters segmentationgenes(hoxgenesandothers)bearsome specifically point to a close relationship between relevance.The genes Antp and abd-A are in the Hexapoda(orperhapsonlyInsecta)andMalacostraca.In plesiomorphicconditionexpressedinthemajorpart the ontogeny ofthe nervous system there occur of the trunk,as in Branchiopoda.In an isopod individualneuroblasts(perhapstrueforallCrustacea), (Malacostraca)Antpwasfoundtobelargelyrestrictedto andtheseshowaparticulararrangementontheventral theperaeon,whileabd-A isrestrictedtothepleon, sideofthesegmentsaswellasaspecialsequenceof resemblingthelimitationofAntptothethoraxandofabd- cleavages(Simpson,２００１;Dohle,２００１;Harzsch,２００３). AtotheabdomeninInsecta(AbzhanovandKaufman, Inaddition,MalacostracaandInsectashareasimilarset ２０００).InbothInsectaandIsopodathelastsegmentof ofnervecellstransmittingthevisualstimulustothe theposteriortagma(bearingtheuropodsorcerci)lacks opticganglia(Nilsson andOsorio,１９９７)aswellas abd-A expression.ThegeneUbx,however,showsno structuralcomplicationsintheopticneuropils,suchas congruence:expressionintheisopodperaeonandthe thepresenceofalobulaandnervechiasmatabetween abdomen.The evidence is thus somewhat theneuropiles(Sinakevitchetal.,２００３).However,the contradictory(HughesandKaufman,２００２).Whetherin charactersofthevisualsystem areactuallyambiguous caseofhomologythemalacostracanorthehexapodan sincetheapomorphiesarepartlyabsentinthebasaltaxa typeoftagmatisationisplesiomorphicwouldappear LeptostracaandArchaeognatha.Incontrasttomorphol- ambiguous. ogy,molecularanalysespredominantlyindicateBranchio- [２]Consideringtheposteriortentorialapodemesa podatobetheclosestrelativesofHexapoda(asfaras synapomorphyofthehexapodlineagesrequiresthe Hexapodaappearsasamonophylum;e.g.,Babbittand homology ofcertain head apodemesin Collembola, Patel,２００５;Regieretal.,２００５;MallattandGiribet, Diplura,andInsecta(Manton,１９６４;Boudreaux,１９７９: ２００６). １３３;Koch,２０００a;Willmann,２００３),which,however,is disputed(BitschandBitsch,２００２).Inaddition,many MonophylyofHexapoda Malacostracahaveapodemesofverysimilarlocation Hexapodmonophylyisonlyweaklysupportedfrom (betweenthetwomaxillarysegments;Snodgrass,１９５１; themorphologicalside.Thereismuchambiguityinthe Lauterbach,１９７０:１０５;Scheloske,１９７７;Marvillet,１９７８, interpretationofmostoftherelevantcharacters,which １９８２;Coleman,２００２),whichthusmightrepresenta ispartlyduetotheuncertaintyregardingthesistertaxon synapomorphy forHexapoda (oronly Insecta)and ofHexapoda(orsistertaxaofitsprincipalsubgroups;see Malacostraca.[３]Theconditionoftwocorneageneous KlassandKristensen,２００１). cellsasprimarypigmentcellsinthecompoundeye Themostwidelyknowncharacterconsideredto ommatidiaand [４]the multi-segmented filamentous supporthexapodmonophylyis[１]thetagmatisationof cerciare not convincing hexapod autapomorphies, thetrunkintothoraxandabdomen.Ifonecompares becauseDipluraandProturalackcompoundeyesand Hexapoda with Myriapoda,the apomorphy is the bothCollembolaandProturadonothaveappendages formation ofan abdomen thatlacks walking legs. thatcanclearlybehomologizedwiththecerci.Other However,in the four major hexapod lineages the apomorphiessharedbythemajorlineagesofHexapoda abdominalappendagesaredifferentiatedinverydifferent areambiguousbecausetheyarealsopresentinmyriapod ways:highlyspecialized(andhardlyreduced!),basally subgroups,suchas[５]fusionofthesecondmaxillaeinto fusedappendagesofsegments１,３,and４inCollembola alabium (alsoinSymphylaandperhapsintheground (ventraltube,retinaculum,manubrium);pairedstumps planofTracheata:Fanenbruck,２００３:２６８ff;Bitschand withoneorfewpodomeresonabdominalsegments１–３ Bitsch,２００４:５３５).WhencomparingHexapodawith inProtura;flatcoxallobeswithstyliandcoxalvesicles Myriapoda,onemightalsoassumethat[６]theabsence on the pregenital (and partly genital) abdominal ofspiraclesinthefirstpostcephalicsegmentcouldbea segmentsinDipluraandInsecta(coxitesinmosttaxa hexapodautapomorphy(Fanenbruck,２００３),butthisis ６ K.-D.KLASS

alsoambiguous(KlassandKristensen,２００１:２８３f). Dipluraisdisputed(Koch,２０００aandFanenbruck,２００３ There isalso morphologicalevidence fornon- vs.BitschandBitsch,２０００,２００４).[１３]Thephylogenetic monophyleticHexapoda.[７]Forinstance,Insectaand evidence from the１０-segmented dipluran abdomen Malacostracashareflagellateantennaewithmusculature (Koch,１９９７;Machida,２００６)isunclear,becausethe onlyinthebasalantennomeres(４inLeptostraca,２–３in numberofabdominalsegmentsinthehexapodground Eumalacostraca,１in Insecta;Claus,１８８８;Schmidt, planisunknown(KlassandKristensen,２００１:２６７). １９１５: Fig.１１; Cochran,１９３５; Snodgrass,１９３５; Evidencecontradictingdipluranmonophylycomes Lauterbach,１９７０).[８] Characters from the optic from [１４]the structure ofthe ovaries.In Diplura- neuropilescouldalsobeviewedassupportinginsect- CampodeinathesearestructuredasinCollembolaand malacostracanrelationships(e.g.,presenceofalobula; Protura,altogethersac-likeandnotsubdivided,and(as seedatainSinakevitchetal.,２００３). inCollembola)withameroisticgermarium-vitellarium Manymolecularstudiessupportamonophyletic area.TheovariesofDiplura-Japyginaresemblethosein Hexapoda(RegierandShultz,１９９８,２００１;Wheeleretal., basalInsecta,withacomb-likedivisionintoovariolesand ２００１;Kjer,２００４;Regieretal.,２００５;Kjeretal.,２００６; apanoisticgermarium-vitellarium area.(e.g.,Štysand MallattandGiribet,２００６).Theseresultsarebasedon Biliński,１９９０;BilińskiandSzklarzewicz,１９９１;Štyset datafrom １８S,２８S,EF-１α,and EF-２,aswellas al.,１９９３;Kristensen,１９９７;BitschandBitsch,１９９８, combinedanalysesofthemitochondrialCOI,COII,１２S, ２０００;Heming,２００３).Nonetheless,thephylogenetic and１６S.Non-monophyletic Hexapoda were mainly interpretationoftheovarycharactersisdifficult. obtainedinanalysesofshortgeneslikeH３andsnRNA- AmonophyleticDipluraisfoundinthemorphology- U２(Edgecombeetal.,２０００)andofsubsetsofthefast basedcladisticanalysesbyBitschandBitsch(２０００)and evolvingmitochondrialsequences(Nardietal.,２００３a; Giribetetal.(２００４:Fig.１),butnotinthatofBitschand Cooketal.,２００５;Carapellietal.,２００５),andinsomePOY Bitsch(２００４).Themoleculardataunequivocallysupport analyses(GiribetandRibera,２０００;Giribetetal.,２００１, Diplura(Wheeleretal.,２００１;Giribetetal.,２００４:Fig.２; ２００４:Fig.２). Kjer,２００４;Luanetal.,２００５;Kjeretal.,２００６).Together Duetothisconflictingevidencefrom both the with the prevalence ofmorphologicalcharacters in morphologicalandthemolecularside,themonophylyof favourofDiplura,thiswouldrenderthemonophylyof Hexapodashouldcurrentlyberegardedasuncertain thistaxonquitewell-supported. (whilethefollowingchapter３isbasedonitspreliminary acceptance).Theproblemcanprobablyonlyberesolved MonophylyofInsecta(=Ectognatha) byphylogeneticworkcoveringtheentireMandibulata, Thistaxonisstronglysupportedbymorphological whichwillrequireconsiderableeffortswithregardto characters(BitschandBitsch,２００４;BeutelandGorb, comparativemorphology. ２００６)andalsowidelyconfirmedbymolecularanalyses (Wheeleretal.,２００１:Fig.１２A;Giribetetal.,２００４:Fig.２; ３.BasalrelationshipsinHexapoda Mallatetal.,２００４;Kjer,２００４;Regieretal.,２００５;Luanet MonophylyofDiplura al.,２００５;Kjeretal.,２００６;MallattandGiribet,２００６). Characterssupportingthisgroupare[９]atongue- OnestrikingautapomorphyofInsectais[１５]the and-grooveconnectionofthemaxillarygaleaewiththe femaleovipositorventrallyonabdominalsegmentsVIII hypopharyngealsuperlinguae(François,１９７０:Fig.１０; and IX (see Klass,２００３a:１９５ff,２００８foritsbasic Kristensen,１９９８)and[１０]aspecialtypeofentognathy pattern).Itiscomposed ofthe coxitesofthe two (Koch,１９９７,２０００a,b,２００１)wherethemandiblesand segments(valvifers),theirgonapophyses(=１stand２nd maxillaeofonesideareenclosedinacommonpouch.In valves,derivedfrom coxalvesicles:Bitsch,１９９４),the theontogeneticdevelopmentofentognathyinDiplura posteriorlyprolongatedcoxallobesofsegmentIX(３rd thelabialpartsbecome rotated(IkedaandMachida, valves orgonoplacs),and severalsmallersclerites １９９８;Machida,２００６;SekiyaandMachida,２００９),and aroundthevalvebases,amongthem remnantsofthe the dorsum ofthe maxillary segmentforms parts eusternites.The１stand２ndgonapophysesofasideare (admentum;François,１９７０:AdinFig.２;Ikedaand interconnectedbyatongue-and-groovesystem (rhachis Machida,１９９８)thatlaterareplacedlateraltothelabium; + aulax=olistheter).Theplesiomorphicpositionofthe thesefeaturesmightbefurtherapomorphiesuniting femalegenitalopeningislikelyonthehindmarginof Diplura.Manton (１９７２,１９７７)proposed that[１１]a segmentVII,as in and bipartite and twisted condition ofthe trochantero- (Rousset,１９７３;Bitsch,１９７４).Another conclusive femoralmuscle,onebundleofwhichextendsfarintothe apomorphyis[１６]therestrictionofmusculaturetothe femur is an autapomorphy of Diplura. However, basalmostantennomereandthepresenceofJohnston's reinvestigationsbySzucsichandPass(２００８)letthis organinthesecond(whileanunmuscledflagellum as characterappeardoubtful.[１２]Whetheralossofthe suchissharedwithMalacostraca,seeabove).[１７]The anteriortentorialarmsisapotentialautapomorphyof posteriortentorialarmsarefusedmediallytoform a HEXAPODPHYLOGENY:ACRITICALREVIEW ７

transversetubeorbeam (whilesimilar–butmedially (postantennalorgans)and Protura (pseudoculi)but separated–apodemesaresharedwithmanyMalacos- absentinDipluraandInsecta.[３１]Therectalampullae tracaandperhapsotherHexapoda,seeabove).[１８]The and papillae ofthe hindgut are perhaps another tarsusissubdividedintoseveraltarsomeres(e.g.,Sturm apomorphycommontoDipluraandInsecta(Bitschand andMachida,２００１).[１９]Theclaw-bearingpraetarsusis Bitsch,１９９８).[３２] The similar structure ofthe reduced,wherebythebasesoftheclawsareincontact abdominalappendagesmayalsosupportthisclade:coxal withthedistalmarginofthelasttarsomere.[２０]The lobeswithcoxalsclerites(=coxites,oftenfusedwiththe dorsaltip ofthe abdomen bearsalong,articulate eusternite)bearingstyliandcoxalvesicles.[３３]Paired terminal filament (=caudal filament, paracercus; pretarsalclawsand[３４]themulti-segmentedfilamen- reduced in Pterygota other tous cercimay provide further support,but the thanEphemeroptera).[２１]Theantennalvesselsare phylogeneticinterpretation isambiguous(Klassand separatedfromtheaorta(Pass,１９９１,１９９８,２０００;Passet Kristensen,２００１:２６８). al.,２００６).[２２]Thelabialglandsopenontheanterior AcladeCollembola+ Protura(=Ellipura)hasnot baseofthelabiumandleadintoasalivariumenclosedby beenobtainedinmorphology-basedcladisticanalyses thelabium andhypopharynx(BitschandBitsch,２００４). (BitschandBitsch,１９９８,２０００,２００４;BeutelandGorb, Intheembryo[２３]theserosafoldsovertheventralside ２００１,２００６;Giribetetal.,２００４:Fig.１;seealsoKoch, frombothsidesandafteritsclosureformsatransitional １９９７,２０００a,b,２００１).Yet,[３５]thespecialform of cavity;atleastpartoftheinnerfoldwallsoriginatesfrom entognathy(seeabove)isperhapsagoodargument, embryonictissue,thusrepresentinganamnion(Machida whileitalsoappearspossiblethatthedipluran-type andAndo,１９９８;Machidaetal.,２００２;Masumotoand entognathy is derived from it. Further ellipuran Machida,２００６;Machida２００６).[２４]Theappendagesof apomorphiesare[３６]thegroove-like“lineaventralis” abdominalsegment１transitionallyformglandularpleuro- alongtheventralmidlineofthelabium andcervical podia(Machida,１９８１;Sturm andMachida,２００１:１５９, region (Willmann,２００５a:Fig.A.６) and [３７] the １７３;Heming,２００３:１３４). transformationofdistalpartsoftheanteriorabdominal appendagestovesicle-likestructures(apicalvesiclesof RelationshipsbetweenCollembola,Protura,Diplura,and ventraltubeinCollembolaandofabdominalappendages Insecta １–３inProtura;seeKlassandKristensen,２００１:２７７). ThegroupingofCollembola,Protura,andDiplura AcladeCollembola+Diplura+Insectaisindicated intoataxonEntognatha(e.g.,Hennig,１９６９;Boudreaux, by[３８]acharacteroftheprimaryembryonicsheath １９７９)hasbeenbasedonthereductionof[２５]the (serosa):ProturaaretheonlyHexapodainwhichthe compound eyes and [２６] the Malpighian tubules; serosacontributestothefinaldorsalwalloftheanimal, nonetheless,undertheTetraconatahypothesistheweak asinCrustaceaandMyriapoda,whileintheremaining developmentofthe latter is more parsimoniously hexapods this feature has become lost(Fukuiand consideredplesiomorphic.[２７]Theinclusion ofthe Machida,２００６;Machida,２００６). mandibles and maxillae in deep head pouches Mostmolecularanalyseshaveobtainedaclade (entognathy)isafurtherargument.Thestructureand Diplura+ Protura(Wheeleretal.,２００１:Fig.１２A; ontogenyofthepouchesandsurroundingpartsdiffer Giribetetal.,２００４:Fig.２;Kjer,２００４;Luanetal.,２００５; stronglybetweenEllipura(=Collembola+Protura)and Kjeretal.,２００６;MallattandGiribet,２００６),basedona Diplura (Koch,１９９７;Kristensen,１９９８;Ikeda and varietyofdifferentanalyticalmethods,andoftenwith Machida,１９９８;Machida,２００６):mandiblesandmaxillae strongsupport.Collembolaaremostfrequentlyfoundas inseparatepouchesinEllipurabutinasinglepouchin thesistergrouptoDiplura+Protura(Kjer,２００４;Luanet Diplura.However,inallentognathansthe“mouthtube” al.,２００５;Kjeretal.,２００６;MallattandGiribet,２００６), isformedbyhypertrophiedlateralcranialfoldsthatgrow confirmingtheEntognathahypothesis;onlyinWheeler overthemandiblesandmaxillaeandfusewith the etal.(２００１:Fig.１２A)theyaresistertoInsecta. labrum and labium, and this stillconstitutes an Inconsequence,therelationshipsamongCollembo- apomorphysharedamongtheentognathantaxa. la,Protura,Diplura,andInsectaremainunclear. OtherargumentsfavouracladeDiplura+ Insecta: [２８]Theflagellum ofthespermatozoahasanadditional ４.BasalrelationshipsinInsecta outercylinderofninemicrotubuli(Dallai,１９９８;Jamieson MonophylyofArchaeognatha etal.,１９９９).[２９]In theembryonicdevelopmenta Thisissupportedby[３９]theverylarge,dorsally secondaryembryonicsheathisformed(amnion)that contiguouscompoundeyes,[４０]thebilobedglossaand growsfromthemarginsoftheembryoaroundtheentire paraglossa,[４２]atriangularprojection on the first egg and displaces the serosa (Ikeda and Machida, maxillarypalpomere,and[４３]theabsenceoftracheal ２００１;Machida,２００６:Fig.４;SekiyaandMachida,２００９). spiracles on abdominalsegment１(see Sturm and [３０] Temporal organs are present in Collembola Machida,２００１:Figs.８.８,８.９,８.６２,８.６３).Sturm and ８ K.-D.KLASS

Machida(２００１:１８９f)andBitschandBitsch(２００４)list few subgroupsofPterygota(e.g.,MatzkeandKlass, further potential autapomorphies, most of which, ２００５:１１２, references therein). For two further however,appearlessconclusiveintheoneortheother charactersthepolarityisunclear:[５１]Theseptum that way. separatesthelumenofthecercusfrom theremaining hemolymphspaceisnon-muscularinArchaeognathabut MonophylyofDicondylia muscular in Zygentoma s.str.and Ephemeroptera [４４]Themedianfusionoftheanteriortentorial (Gereben-KrennandPass,１９９９,２０００;Passetal.,２００６). armsappearstobeuniquetotheDicondyliaandclearly [５２]Ontogeny starts with a completely superficial supportsthisgroup.Allothercharactersareambiguous cleavage(Kristensen,１９９８;Sturm andMachida,２００１: tosomeextent:[４５]Theadditionalanteriorarticulation １７３;seedatainBitschandBitsch,１９９８forambiguous betweenmandibleandheadcapsule(Staniczek,２０００; polarity). FürstvonLieven,２０００;Koch,２００１:１５３)and[４６] ThemonophylyofDicondyliaissupportedinall theepistomalsulcus(clypeofrontalsulcus;traversing morphology-basedcladisticanalyses(BeutelandGorb, betweentheanteriorbasesofthemandibles)areamong ２００１,２００６;BitschandBitsch,２００４;Giribetetal.,２００４: the mostwell-known autapomorphies proposed for Fig.１)aswellasinmostmolecular-basedanalyses .ThearticulationisfairlylooseinZygentoma (Wheeleretal.,２００１:Fig.１２A;Kjer,２００４;Luanetal., s.str.,Tricholepidion,andnymphsofEphemeroptera ２００５;Kjeretal.,２００６;MallattandGiribet,２００６).Onthe (actuallytwocloselyadjacentarticulationswiththebase otherhand,Edgecombeetal.(２０００)didnotfinda oftheanteriortentorialarm andthemarginofthe monophyletic Dicondylia using H３ and U２ snRNA clypeus),whileOdonataandNeopterahaveatightball- sequences.Regieretal.(２００４)in theircombined and-socket joint. However, Collembola also show analysisofEF-１α,EF-２,andPol-IIfoundsupportfor articulation-likedifferentiationsattheanteriorbaseof Archaeognatha+ Zygentoma assistertoPterygota the mandible,and in Archaeognathathe membrane (based on severalanalyticalmethodsbutwith low betweenthescleritemarginsisverynarrow (Koch, support).Kjeretal.(２００６)foundthatthemitochondrial ２００１).Furthermore,dicondylicmandiblesare wide- COI,COII,１２S,and１６Sdataalsosupportsuchaclade. spreadinMyriapoda(e.g.,Rilling,１９６８forChilopoda) Giribetetal.(２００４:Fig.２)obtainedArchaeognatha+ andMalacostraca.Insome subgroupsofMalacostraca ZygentomaasasubgroupofPterygotabasedonnuclear theanteriorarticulationshowsaverysimilarstructure rRNA,COI,１６S,andH３sequences. andlocation(ontheheadcapsule)asinDicondylia,andis alsoassociatedwithanepistomalsulcus(e.g.,Schmidt, MonophylyofZygentomas.str.(excl.Tricholepidion) １９１５;Snodgrass,１９５０;Manton,１９６４;Lauterbach,１９７０; Zygentoma s. str. includes the , Marvillet,１９７８).[４７]Thegonangulum-scleriteofthe (incl.Atelurinae),Protrinemuridae,and ovipositorisevenmoredoubtfulasanautapomorphy (Koch,２００３).Itsmonophylyisdifficultto ofDicondylia,because its two precursor sclerites substantiate.[５３]The flathabituswith horizontally (laterocoxite and praecoxite in Bitsch,１９７４;Klass, orientated,dorsoventrallyflattenedcoxaeandfemora ２００３a:Fig.６４)arestillseparatedinovipositor-bearing andwithcoxalexcavationsreceivingthefemora(Koch, Odonata(fusedonlyinEpiophlebia)andsome basal ２００３;Willmann,２００３,２００５a;BitschandBitsch,２００４;all Dermaptera,astheyareinArchaeognatha(Klass,２００３a: less distinct in Tricholepidion) was a favourable ２０２,２００８). preconditionfortheevolutionofflight(Hasenfuss,２００２) Regardingsome furtherapomorphiessharedby andmaythusbeplesiomorphicforDicondylia.[５４]The Zygentomas.str.andPterygota,dataonTricholepidion roundlensesoftheommatidia(Koch,２００３)arenotvery are lacking,and these apomorphies eithersupport conclusiveinviewofthegeneralreductionofcompound Dicondylia,orDicondyliaexcludingTricholepidion:[４８] eyesinZygentoma.[５５]Thelossofocelliisalsonotvery Thetrachealsystem hasregularconnectionsbetween convincinginviewofthemultipleindependentlossof thetwosidesofasegmentandbetweensuccessive ocelli in Neoptera. [５６] The conjugation of the segments.Diplurahavealmostexclusivelylongitudinal spermatozoaisstructurallyinhomogeneous(seebelow). connections (Bitsch and Bitsch,１９９８),for which A few characters contradictthe monophyly of positionalcorrespondencewiththoseinDicondyliais Zygentomas.str.:[５７]Thefusionoftheanteriorand unclear,andArchaeognathahaveatmostsomescattered posteriorpartsofthetentorium inMaindroniidaeand longitudinalandtransverseconnections(Stobbart,１９５６; Pterygota(Koch,２００３)isapotentialsynapomorphyof SturmandMachida,２００１).[４９]Theegghasamicropyle thesetaxa.[５８]Winglikeprocessesontheanterior forfertilization(Sturm andMachida,２００１:１７３).[５０]In tentorialarmsthatbearpartofthemandibularadductor thematureembryothefronsoftheheadbearsan attachmentsoccurinLepismatidaeandMaindroniidae unpairedeggtooth(Sturm andMachida,２００１:１７３); (Koch,２００３) but also in at least Mantodea and however,aneggtoothhassofarbeenreportedonlyfor PhasmatodeaamongthePterygota(KlassandEulitz, HEXAPODPHYLOGENY:ACRITICALREVIEW ９

２００７;seemuscle２１inLevereault,１９３８forMantodea). dorsalbaseofthecerciisincontactwiththehindmargin Zygentoma s.str.varyalotwithregardto[５９]the oftergite１０(Klass,２００１a:Figs.２９–３６),anddorsal presenceofstyliandcoxalvesiclesandthefusionof longitudinalmusclesofsegment１０cometoactascercal coxitesandeusterniteinthepregenitalabdomen(e.g., muscles.[７１] The delimitation oflateralcervical Bitsch,１９７９:３４４f).Since Pterygota always lack scleritesfrom prothoracicsclerotizationscouldbea pregenitalstyliandcoxalvesicles,andhavecoxitesand furtherautapomorphyofPterygota(Boudreaux,１９７９: sternitesfused,thischaractercomplexwouldinclude １８９;Weidner,１９８２:１５４),butaclearinterpretation apomorphiessharedbetweenPterygotaandsubgroups requiresacomprehensiveevaluationofthepublished ofZygentomas.str. dataacrossInsecta. Giribetetal.(２００４:Fig.２)andRegieretal.(２００４, Ontheotherhand,[７２]theevidencefromthefusion ２００５)aretheonlymolecularcontributionsthatinclude oftheanteriorandposteriorpartsofthetentorium is morethanonefamilyofZygentomas.str.:Lepismatidae ambiguous(seecharacter[５７]).[７３]Thedirecttransfer andNicoletiidae.Intheiranalysesthesetaxagroup ofaspermatophore(orsperm)tothefemalegenitaliavia together,butoneshouldnotethatinthesameanalysesa amalecopulatoryorganisalsoanambiguouspterygotan cladeArchaognatha+Zygentomaisobtained. autapomorphy,becauseatransferfrom themalegenital openingtothefemaleisfoundinEphemeropteraand MonophylyofPterygota Neoptera,whereas in Odonata the sperm is first Withtheevolutionofflighttheentireskeletomuscu- transferredfrom themalegenitalopeningtoamale larsystem ofthe thorax has undergone extensive copulatoryorganonabdominalsegments２and３,and structuraltransformation(Boudreaux,１９７９;Hasenfuss, onlythentothefemalegenitalia. ２００２,２００８).The most evident autapomorphy of Mostmolecularstudiesconfirm themonophylyof Pterygotais[６０]thepresenceofwingsonthemeso-and Pterygota(Wheeleretal.,２００１;Hovmölleretal.,２００２; metathorax.Atanearlystageofwingevolutionallthree TerryandWhiting,２００５;Kjeretal.,２００６;Mallatand thoracicsegmentswereinvolved,asshownbysmall, Giribet,２００６).OnlyGiribetetal.(２００４:Fig.２)obtain winglike,veinedlaterallobesontheprothoraxofmany Archaeognatha+ZygentomaasasubgroupofPterygota, CarboniferousPterygotafrom severalmajorsubgroups and Giribetetal.(２００１)find the long branch taxa (e.g.,Kukalová-Peck,１９７８,２００８;Bechlyetal.,２００１; DrosophilaandJapygidaeinagroupwithCrustacea, GrimaldiandEngel,２００５).Thewingsconstituteavery remote from other pterygotans. In Kjer (２００４) complexcharactersystem comprisingmanyfeaturesof Tricholepidionis,withweaksupport,nestedinPterygota thevenationandbasalarticulationthataresharedbyall assistertoOdonata. Pterygota.Furtherautapomorphiesinthepterothoracic segmentsofPterygota(accordingtoHasenfuss,２００２, RelationshipsbetweenTricholepidion,Zygentoma s.str., ２００８)are[６１]thefusionofcertainscleritesbetween andPterygota coxaandwingbasethatformerlyhadbeendiscrete AmongthesynapomorphiesproposedforTrichole- podomeres;[６２]theextensivesclerotizationofformerly pidionandZygentomas.str.,[７４]thefour-segmented membraneousareas;[６３]thepleuralsulcus;[６４]the labialpalps (Staniczek,２０００)is perhaps the most separation ofthe basalar sclerite from the other convincing,asthisisapparentlyneitherreportedfor sclerotizationsofthemostproximalformerpodomere; apterygotesnorforbasalPterygota.Allothercharacters and[６５]theformationofthesubalarsclerite.Afurther areproblematic.Parallelevolutionisrequiredfor[７５] characteris[６６]thedelimitationofaposteriorsclerite thereductionofthehypopharyngealsuperlinguae(also portion(scutellum)byacurvedsulcus.Thescutellum trueformostPterygota),andfor[７６]theenlargedapical alsoservesasapumpcasefortheunderlyingenlarged labial palpomere (also found in some Pterygota partoftheheart(Pass,２０００).Inthecirculatorysystem andArchaeognatha;seeStaniczek,２０００;Sturm and (Pass,１９９１,１９９８;Passetal.,２００６),[６７]thepaired Machida,２００１:８６).[７７]Somekindofspermconjugation circumoesophagealvessels are absent (present in ispresentinTricholepidionandallfamiliesofZygentoma Collembola,Diplura,Archaeognatha,andZygentoma). s.str.,butitisachievedinseveraldifferentwaysthatcan [６８]Thelegshavediaphragmsconsistingofconnective hardlybeconsideredasincludingasharedapomorphy tissue,which separate the distally and proximally (Dallaietal.,２００１,２００２,２００４).[７８]Thehook-like directedhemolymphcurrents.[６９]Theendoskeleton condyleatthedorsalbaseofthecercithatisarticulated made from connective tissue,which in apterygote upon thefree,overhanginghindedgeofabdominal Hexapodaservesfortheattachmentofmanymuscles, tergite１０(Koch,２００３)couldindeedbeaprecursor hasbeenlostalmostcompletely(Birket-Smith,１９７４; structureofthesimplerarticulationbetweencercalbase Boudreaux,１９７９:１８８;seecharacter[１１２]forvestigesin andhindmarginoftergite１０inmanyEphemeroptera Dictyoptera).[７０]Thelateralpartsofabdominaltergite andNeoptera(intercorrelatedwithcharacter[７０];Klass, １１arereducedandfragmented,orabsent.Therebythe ２００１a).The articulation could thus as wellbe an １０ K.-D.KLASS

autapomorphyofDicondylia.TricholepidionandNicoletii- gap between certain axillary sclerites and their daeshare[７９]specialsensillaon theundersideof associatedwingveins,andflexionlineswithinthewing the terminalfilamentofmales(Wygodzinsky,１９６１; base(e.g.,Hennig,１９６９:１５１f,Fig.２５A;Boudreaux, Kristensen,１９９１);however,are-examinationofthis １９７９:２０１;Hörnschemeyerand Willkommen,２００７). characterinaselectionofZygentomaandEphemero- Neopteryallowsforenteringcleftsorcrevicesinorder pteraspeciesisadvisable. tosearchforfoodorshelter,anditfurthermoreenables A cladeZygentoma s.str.+ Pterygotareceives adaptationtolifeinnarrowspaceswithouttheneedto supportfrom[８０]thecompletelossoflateralgenalfolds giveuptheabilitytofly.Itoftengoesalongwitha andresultingexposureofthemouthpartbases;[８１]the hardeningoftheforewingsintotegminathatalsoprotect lossofthezygomaticligamentconnectingtheventral themoredelicatehindwings. mandibularadductorsofthetwosides;[８２]theorigin Inrecentyears,however,manyleadingworkers ofthe posteriormostmandibular adductors on the havetendedtoconsiderneopteryastheplesiomorphic tentorium (Staniczek,２０００fortheseheadcharacters); conditionforPterygota(Brodsky,１９９４;Willmann,１９９８; and by [８３]the non-segmentalarrangementofthe Kukalová-Peck,２００８;Willkommen,２００８;Hörnsche- ovarioles(Barnhart,１９６１:１９２;BitschandBitsch,１９９８) meyerandWillkommen,２００７,leavethequestionof contrasting the segmentalarrangementin Japygina, polarityopen).Palaeoptery,foundinEphemeroptera, Archaeognatha,andTricholepidion (Štysetal.,１９９３: Odonata,and most Palaeodictyopteroidea†,is then Table１,Fig.２).Staniczek(２０００)proposes[８４]the regardedashavingevolvedseveraltimesindependently; presence ofamuscle connecting the mandible and for Ephemeroptera and Odonata it is variously hypopharynxasafurtherargument,butasimilarmuscle consideredhomologous(e.g.,Kukalová-Peck,２００８)or isfoundinArchaeognathaandCollembola(Bitsch,１９６３: homoplastic(Willkommen,２００８). ６３２). [８６]Thearoliumbetweenthepraetarsalclawsmay Amongthemorphology-basedcladisticanalyses, beanautapomorphyofNeoptera(BeutelandGorb, TricholepidionissistertoZygentomas.str.inGiribetet ２００６),butifsoithasbeenlostsofrequentlythatinthe al.(２００４:Fig.１),buttotheremainingDicondyliain cladisticanalysisofBeutelandGorb(２００６)itisnot BeutelandGorb(２００１)andBitschandBitsch(２００４). confirmedassuch.[８７]Thegonoplacsoftheovipositor BeutelandGorb(２００６)obtainanunresolvedtrichotomy formingasheatharoundthetwopairsofgonapophyses ofTricholepidion,Zygentoma s.str.,and Pterygota. (e.g.,Kristensen,１９７５;GrimaldiandEngel,２００５:１５８) Molecularanalysesarealsocontradictory.１８Sdataalone isnotaconvincingautapomorphyofNeoptera,asthis letTricholepidionappearasthesistergroupofOdonata conditionisdiscreteonlyinafewneopteransubgroups, (butwithweaksupport;Kjer,２００４).Kjeretal.(２００６), while others (e.g.,Dermaptera,Dictyoptera) do includingseveralgenes,obtainedTricholepidionsisterto notdiffer distinctly in this respectfrom Odonata theremainingZygentoma.InGiribetetal.(２００４:Fig.２) (Ephemeropteralackanovipositor). TricholepidionissubordinateinZygentoma.Terryand Neoptera resultas monophyletic in nearly all Whiting(２００５),applyingvariousalignmentparameters molecular-based phylogenetic analyses,based on a to１８S,２８S,andH３sequences,foundTricholepidionas varietyofnuclearandmitochondrialgenesanddifferent thesistergroupofZygentomas.str.+Pterygota. analyticalmethods(Wheeleretal.,２００１;Hovmölleret Theevidenceconcerningtherelationshipsbetween al.,２００２;Kjer,２００４;TerryandWhiting,２００５;Kjeretal., Tricholepidion,Zygentomas.str.,andPterygotaisthus ２００６;MallattandGiribet,２００６).InsomeofCameronet extremelycontradictorybothbasedonmorphological al.’s(２００６a;mitochondrialgenome)analyses,however, andmoleculardata.SincethemonophylyofZygentoma theOdonataaresubordinateintheNeoptera(closeto excl.Tricholepidionisalsohardlysupported,thebasal Orthoptera),thoughwithlowsupport. splittingeventsinDicondyliaarealtogetherobscure. Relationships between Ephemeroptera,Odonata,and ５.BasalrelationshipsinPterygota Neoptera MonophylyofNeoptera Therelationshipsbetweenthesetaxahavelong Thiscladeisdifficulttoarguefromamorphological beencontroversial,andallthreepossiblehypotheses perspective.[８５]Neopteryhaslongappearedasthe stillreceivesupportbypartofthedata.Charactersofthe mostevidentautapomorphyofthisclade.Itmeansthe flightapparatusaredifficulttoapplytothisproblem, abilitytoswingbothpairsofwingsbackwardhorizontally becausethebasalmostdichotomyinPterygotaishere sothattheylieontheabdomen,forewingscovering theissue,andpotentialoutgrouptaxaarewingless(wing hindwingsandallanteriorwingmarginsdirected(ventro-) charactersarebrieflysummarisedinWillkommen,２００８: laterally.Thisneopterousconditionisbasedonaspecial ２９０ff). architectureofthe３rdaxillary,aspecialfunctionofthe ThehypothesisofaOdonata+ Neopteraclade (plesiomorphic)muscleattachedtoit,amembraneous (=Metapterygota)appearsmostconvincingfrom the HEXAPODPHYLOGENY:ACRITICALREVIEW １１

morphologicalpointofview (Kristensen,１９９１;Beutel ２００８),Bechlyetal.(２００１),andSoldán(２００３),hasbeen and Gorb,２００６). [８８] The anterior mandibular advocatedmainlybasedoncharactersfromthevenation articulationisaball-and-socketjointwiththeginglymus andarticulationofthewings,thoughforsuchcharacters (acetabulum)onthemandibleandthecondyleonthe polarityisdifficulttoargue.Onecharacterconcerns[９８] head capsule (Staniczek,２０００).In correlation with the presence of intercalary veins: parts of the the resulting limitation ofmandibular movements, archaedictyon(anetworkofcrossveinsbetweenthe [８９]severalmandibularmuscles have become lost mainwingveins)arerearrangedtoform long,straight (Staniczek,２０００). Nonetheless, the very similar linesin between the main veins.Itisnoteworthy, articulationinmanyMalacostracamustbekeptinmind however,thattheputativelymostplesiotypicOdonato- (seecharacter[４５]).[９０]OdonataandNeopteradonot ptera(CarboniferousGeroptera)neitherhadintercalary haveimaginalmoultsasEphemeroptera(fromsubimago veinsnoranarchaedictyon(e.g.,Willmann,２００５a:２９; to imago),Zygentoma,and Archaeognatha(frequent GrimaldiandEngel,２００５:１７４).[９９]A basalbrace imaginalmoults,Sturm andMachida,２００１:１７５,１８５). betweentheposteriorcubitalandanterioranalveins [９１]Themeso-andmetathoraciclegsandalsothewings (cup–aa１)alsooccursinPlecoptera(Béthoux,２００５). aresuppliedbytwotrachealstemseach,whichcome [１００]A commonstem oftheanteriorandposterior from thespiraclesofthesame andofthefollowing sectorsofthemedia(MA,MP;HaasandKukalová-Peck, segment.InZygentoma andEphemeroptera(usually) ２００１:４９４,Table６A)isalsowide-spreadinNeoptera(see thelegsandparanotaorwingsaresuppliedonlybyone Kukalová-Peck,１９９１;Kristensen,１９９１:１３１).[１０１]The trachealstem from thesame segment(Ander,１９３８; shortantennae (Hennig,１９６９)have likely evolved Kristensen,１９７５).[９２]Theheartisclosedposteriorly independently in Odonata and Ephemeroptera,as and lacks a valve in its abdominalportion;the distinctly longer antennae probably occurred in hemolymphcurrentisthusdirectedanteriadalongthe Palaeozoic relatives ofboth taxa (Brauckmann and entireheart(Passetal.,２００６).InDiplura,Archaeogna- Zessin,１９８９;GrimaldiandEngel,２００５:１６７).Ithasbeen tha,andZygentomatheheartisopenposteriorly,butitis proposed that in nymphs ofboth Ephemeroptera alsoclosedinCollembolaandProtura.[９３]Odonataand and Odonata[１０２]the galeaand laciniaare fused. Neoptera have a nervous connection between the However,thecharacterisambiguousduetoconjectural corporacardiacaandcorporaallata,whichisabsentin homologisationofthetwoterminalmaxillaryprocesses Ephemeropteraandinapterygotehexapods.However, inOdonatawiththepalpus,galea,andlacinia(e.g., foroneephemeropteranspeciessuchanervehasbeen Matsuda,１９６５). reported(seeKristensen,１９７５).Ontheotherhand, The poormorphologicalargumentsforaclade [９４] occlusor muscles on the abdominalspiracles Ephemeroptera+Neopteramostlyrefertodirectsperm (Kristensen,１９９１;BeutelandGorb,２００６)cannotbe transferandtotheflightapparatus,especiallywhich consideredasynapomorphyofOdonataandNeoptera. thoracicmusclegroupscausethemovementsrelevantto First,theocclusorsofOdonataandNeopterashowavery flight(e.g.,Boudreaux,１９７９:１９５f).Thesearguments differentspatialarrangement(Miller,１９６２;Poonawalla, are strongly weakened by problems with character １９６６;Klass,２００８:１０１f);second,the zygentoman polarity. Thermobia has spiracle muscles in the posterior Molecularresultsarecontradictory.Allanalyses abdominalsegmentsthatshow positionalcorrespon- depend much on１８S and２８S rDNA data,and dencewiththoseinmanyNeoptera(Rousset,１９７３; incongruencemainlyresultsfrom analyticaldifferences. KlassandKristensen,２００１:Figs.１４,１５).[９５]Thenear- AcladeEphemeroptera+ NeopteraisobtainedinKjer completereductionoftheterminalfilament(Beuteland (２００４:１８S)andfavouredbyMallatandGiribet(２００６,but Gorb,２００６)isneitheraconvincingcharacter,becausein withEphemeropteraandOdonatarepresentedbyonly some PalaeozoicrelativesofOdonatathefilamentis onespecieseach).Incontrast,Wheeleretal.(２００１:Fig. fairlylongandprobablyjointed(Bechlyetal.,２００１: １２A) recover Odonata + Ephemeroptera.Such a Fig.１２).Atmosta moderate reduction could be PalaeopteracladeisalsosupportedinHovmölleretal. synapomorphicforOdonataandNeoptera.For[９６]the (２００２:１８Sand２８S),butthisanalysisusedanunadjusted absence ofthe tentorio-lacinialmuscle (presentin Clustalalignmentandagapcost７５× thatofnucleotide ArchaeognathaandEphemeroptera,butnotreportedfor changes.TheanalysesbyKjeretal.(２００６)findthesame Zygentoma)and [９７]the absence ofsuperlinguae relationshipsusingthecombineddata,whileseparate (presentinArchaeognathaandEphemeroptera,butnot analysesofbothEF-１α andthe１８S+２８SrRNAsupport inZygentoma;seeKristensen,１９９１:１３１)interpreta- Ephemeroptera+ Neoptera.TerryandWhiting(２００５) tionsareambiguous(Kristensen,１９７５andreferences didnotpresentaseparatemolecularhypothesisand therein). support Odonata + Neoptera under inclusion of The hypothesis Ephemeroptera + Odonata (dubious)morphologicaldata.OgdenandWhiting(２００３) (),favouredbye.g.,Kukalová-Peck(１９９７, showedthattheresultofHovmölleretal.(２００２)is １２ K.-D.KLASS

supported only underanarrow range ofalignment differentdependingonthealignmentparametersused. parameters;usingadditionalsequencedata(１８S,２８S, The conflictsamong the mentioned analysesstems H３)forabroaderselectionoftaxa,andapplyingawider mostly from the analyticalmethodsemployed.The rangeofanalyticalmethodologies,theyconcludethat support values for groupings comprising several theiranalysescouldnotclearlyresolverelationships principallineagesofNeopteraareverylow inmost amongthethreetaxa. cases.Butevenforcladeswithhighsupportvalues, therecanbecontradictoryevidence.Forexample,Terry ６.BasalrelationshipsinNeoptera and Whiting (２００５)and Kjer etal.(２００６)found Thebasicsituation Mantophasmatodea+ Notopterastronglysupportedby Kristensen (１９９１: Fig.５.５) showed a basal nuclearrDNA,while Cameron etal.(２００６b)in an neopteranpolytomyincludingtenlineages:Plecoptera, analysisofthewholemitochondrialgenome,andKjeret Dictyoptera,Notoptera,Dermaptera,Orthoptera,Phas- al.(２００６)usingpartsofit,foundMantophasmatodea+ matodea,Embioptera,Zoraptera,Acercaria,andEndo- Phasmatodeadistinctlysupported. pterygota.LaterMantophasmatodea(describedinKlass etal.,２００２)hasbeenaddedasaneleventhlineage. Morphologicalevidenceonneopteranrelationships Effortstoresolvethispolytomyonamorphologicalbasis Firstitisnoteworthythatseveraloftheprincipal sufferfrom thevastincompletenessofthedatabase lineagesofNeopterashowfeaturesthatappearuniquely (especiallyonthemusculature,nervoussystem,and plesiomorphicattheneopteranorevenpterygotanlevel; internalorgans),andfrom anextensiveinconsistence theabsenceoftherespectivefeaturewouldsupportthe amongcharacters.Altogethertherelationshipsamong monophylyofallneopteranlineagesunderexclusionof theelevenlineagesareobscuredbysuchextensive thelineageinquestion. contradictionsthatsharedapomorphiescanbefoundfor Plecopterashowaparticularlygreatnumberofsuch numerous incongruentgroupings.Cladistic analyses plesiomorphies,thoughformostofthesecharactersthe suchasBeutelandGorb(２００１,２００６)mustbeseenas interpretation includes problems. [１０３] Plecoptera very preliminary because ofthe incomplete data have cercalvessels,which are otherwise found in available.Thesituationisnotbetterwithmolecular- Diplura,Archaeognatha,Zygentoma,andEphemeroptera basedanalyses.Differentdatasetsusuallyyieldvery (conditionunknowninOdonata)butnotinneopterans differentresultsforthebasalneopteranrelationships (Passetal.,２００６:characters１０,１１).However,this (comparee.g.,nuclearsequencesinTerryandWhiting, charactercannotbe judged in the many taxawith ２００５andmitochondrialdatainCameronetal.,２００６b), reducedorabsentcerci(mainlyPhasmatodea,Ortho- andstrongdifferencesmayalsooccurwhenthesame ptera,Acercaria,Endopterygota,Zoraptera).[１０４]In dataaresubjectedtodifferentmethodsofalignmentand plecopterannymphsastrandcomposedofmuscularand treeconstruction(seetreesinTerryandWhiting,２００５). connectivetissuehasbeenfoundthatconnectsthe Itisthusnotsurprisingthatinrecentyearsanumberof upperandlowerwallsofthemaxillarystipes(Moulins, mutuallyincongruentmorphology-ormolecular-based １９６８:ts in Fig.１２;“transverse stipitalmuscle”in hypothesesonbasalneopteranrelationshipshavebeen Moulins,１９６８,Kristensen,１９９１,andBeutelandGorb, proposed. ２００１,２００６).Itshowspositionalcorrespondencewith ligamentousstructuresinZygentoma (Chaudonneret, Molecularevidenceonneopteranrelationships １９５０:dsainFig.４２)andArchaeognatha(Bitsch,１９６３: Wheeler etal.(２００１:Fig.１２A,１８S + ２８S) maxillaryligamentslmx１andlmx２inFig.４５),andhas foundabasalsplitbetween(Phasmatodea+Dictyoptera notbeenreportedforotherPterygota(e.g.,Rähle,１９７０: + Orthoptera + Embioptera + Acercaria) and Table３).However,thesedelicatestrandsmayhavebeen (Dermaptera+Plecoptera+Zoraptera+Endopterygo- overlooked in other studies,and they have been ta).TheanalysesbyKjer(２００４:１８S)andKjeretal. documentedonlyfornymphsofPlecoptera,whilethere (２００６:severalgenes),bothexcludingZoraptera,yielded arenostudiesofthenymphalmouthpartmusculaturein a sistergroup relationship between Plecoptera + otherlowerneopterantaxa.Moreover,Zygentomaand DermapteraandtheremainingNeoptera,whichincluded Archaeognathahave additionalintrinsicstipitalliga- amonophyleticgroupcontainingNotoptera+ Manto- mentslocatedfurtherposteriorly,andthesehavesofar phasmatodea,Phasmatodea+ Embioptera,andDictyo- beenfoundonlyinEmbioptera(Rähle,１９７０:B２inTable ptera.TerryandWhiting(２００５:１８S+２８S,H３)obtained ３andp.２６５).Intheabdominalnervoussystem [１０５] themonophylaPhasmatodea+ Orthoptera+ Embiop- mostNeopterahavealateralnerveBgivingorigintothe tera,Dermaptera + Plecoptera + Zoraptera,and branchestotheventralbodywallandtothemid- Notoptera + Mantophasmatodea; the relationships segmentallateral(dorsoventral)muscles.InPlecoptera among these groups and the remaining neopteran thesebranchesoriginatefrom theventralnerveCand taxa(Dictyoptera,Acercaria,Endopterygota)arevery the dorsalnerve A,respectively,as in Zygentoma HEXAPODPHYLOGENY:ACRITICALREVIEW １３

(Birket-Smith,１９７４)andEphemeroptera(Birket-Smith, Oneofthefewinner-neopteranrelationshipsthatin １９７１).Nonetheless,innervationoflateralmusclesbya recentyearshasbeenincreasinglyconfirmed–though branch ofnerve A is also sporadically found in againwithoutsomecounterevidence–isthesistergroup EmbiopteraandPhasmatodea,andtheformationofa relationship between Acercaria and Endopterygota nerveB isthusanambiguousautapomorphyofnon- (cladePhalloneoptera=Eumetabola).Severalpotential plecopteranNeoptera(KlugandKlass,２００７).Plecoptera synapomorphiesarereportedfortheflightapparatus aretheonlyknownNeopterawhere[１０６]theabdominal (Haasand Kukalová-Peck,２００１;Kukalová-Peck and dorsalnervesA arisefrom theCNSinfrontoftheir Lawrence,２００４;Hörnschemeyer and Willkommen, ganglia (Klug and Klass,２００７),as in Zygentoma ２００７;seealsoBeutelandPohl,２００６:２０４):[１１４]a (HeckmannandKutsch,１９９５).However,Ephemero- sclerotizationonthejugum ofthewing(jugalbar;see ptera(KlugandKlass,２００７)andOdonata(Klass,２００８: alsoHamilton,１９７２a,b;Kristensen,１９９１:１３５);[１１５]a Fig.１６)correspondwiththenon-plecopteranNeoptera broad,lobatebaseoftheradius;[１１６]anelongatebaseof intheoriginofnerveAfrom itsganglion.[１０７]The themedia;[１１７]atriangularshapeofthe２ndaxillary; segmentallyarrangedoutlettubesofthetestisinmany [１１８]anadditionalmuscleinsertingonthe３rdaxillary, Plecopteracanperhapsalsobeconsideredaunique whichthushastwomusclesratherthanonlyone(see plesiomorphy(Zwick,１９８０:６７ff).Altogether,mostofthe alsoMatsuda,１９７０).Notethatthesewingcharacters characterssupportingabasalposition ofPlecoptera cannotbeassessedintheconsistentlywinglesslineages insideNeopteraaresomewhatambiguous.InBeuteland NotopteraandMantophasmatodea.Inaddition,[１１９]the Gorb (２００６) the sistergroup relationship between sternitesofthemeso-andmetathoraxareinfoldedalong PlecopteraandtheremainingNeopterawasbasedon the midline (pterothoracic endosterny; Kristensen, character[１０４],whilecharacters[１０３]and[１０５]–[１０７] １９９１;Willmann,２００５a).[１２０]The male copulatory werenotincluded. organsshow aspecial,probablyapomorphicmodeof Potential unique plesiomorphies of Notoptera ontogeny:a pairofmesomeres fuses to form an are [１０８] the presence of a metathoracic spina aedeagus,besidewhichthereisapairoffree,lateral (posteromedianventralapodeme;Walker,１９３８:ss３in parameres(e.g.,Boudreaux,１９７９:２２２).However,the Fig.３);[１０９]the absence ofaclosing mechanism exposedthoracicsternitesofsome Acercariaandthe (sclerites and muscles)on the abdominalspiracles absenceofanaedeagusinAcercaria-Psocodeaconstitute (Walker,１９４３;ifthis is actually plesiomorphic for problems.[１２１]Structuraldetailsoftheovariolesmay Pterygota:seecharacter[９４]);and[１１０]thepresenceof alsosupportphalloneopteranmonophyly(Büning,１９９４, amedianeversiblesaconabdominalventer１,whichhas １９９８;Kristensen,１９９５).Moreover,there are some beeninterpretedasthemediallyfusedeversiblevesicles apomorphicfeaturesin the female genitalia(Klass, ofthissegment(e.g.,Kristensen,１９９１:１３０)–aview ２００３a:２１９,Figs.７７,７８):[１２２]ThecoxitesIX have consistentwiththepresenceofpairedretractormuscles anterolateralpouchesthatgiverisetolongtendons,and fromcoxosternum１(Walker,１９４３:muscle１４１). [１２３,１２４]thebasalsclerotizationsofbothgonapophyses Two other unique plesiomorphies occur in ８ and９ form laterally directed arms.Nonetheless, Dictyoptera:[１１１]TheproventriculusofmanyBlattaria characters[１２２]–[１２４]cannotbeassessedinanumber isverysimilartothecomplicatedproventriculusof ofacercariansubgroupsandinallEndopterygotaexcl. lepismatid Zygentoma (Klass,１９９８a).However,this Hymenoptera,whichhaveasimplifiedovipositor. issueisambiguousbecausetheproventriculusisvery ThemolecularanalysesinKjer(２００４)andKjeretal. simpleinotherZygentoma andmanyPterygota(see (２００６)weaklyconfirmacladeAcercaria+Endopterygo- Klass,１９９８b).[１１２]BlattariaandIsopteraaretheonly ta,whiletheresultsofWheeleretal.(２００１:Fig.１２A) Neopterathathaveintheirabdomensimplifiedvestiges contradictit,andTerryandWhiting(２００５:combined ofatendinousendoskeleton(Klass,１９９９;Klugand molecular and morphologicaldata) obtain different Klass,２００７):segmentalplateswithinthehyperneural resultsdependingonalignmentparameters. muscle, showing positional correspondence with TheonlyviablealternativetothePhalloneoptera segmentalligamentsofZygentoma(seeKlass,２００１a: hypothesis is a sistergroup relationship between Fig.３７). AcercariaandZoraptera,whichisdiscussedbelow. Auniqueplesiomorphyonthepterygotanlevelis [１１３]thepresenceinmanybasal,ovipositor-bearing Anothergroupingofneopteranlineagesapparently Dermapteraofcoxallobesinthefemalegenitalicregion acceptedbymanyauthorsisthe“,”which notonlyinsegmentIX(３rdvalves=gonoplacs)butalso essentiallycomprisesallNeopteraexceptforAcercaria insegmentVIII(Klass,２００３a:gl８inFigs.１８,２３,４１). and Endopterygota, though depending on the ThiscomplieswiththepresenceofcoxallobesVIIIin authorPlecopteraand/orZorapteramayadditionallybe ArchaeognathaandZygentoma,which areabsentin excluded (see e. g., Hennig,１９６９; Boudreaux, otherPterygota. １９７９;GrimaldiandEngel２００５;Willmann,２００５a;other １４ K.-D.KLASS

names describing groupings of such content are (orevenelytra)inmanyHemipteraandColeoptera.As “Paurometabola”and “Pliconeoptera”).However,this theabilitytoentercleftsorcrevicesisoneofthe assemblageofOrthoptera,Dictyoptera,Phasmatodea, putativeadvantagesofneoptery,boththepresenceof Notoptera,Dermaptera,Embioptera,andMantophasma- some tegminisation in the common ancestor of todeais,whetheradditionallyincludingPlecopteraand NeopteraorevenPterygota(withmanyinstancesof Zorapteraornot,hardlysupported.Manyoftheolder secondaryloss)andafrequentindependentevolutionof argumentswerealreadyfalsifiedbyKristensen(１９７５, tegminisationappearplausible. １９８１,１９９１,１９９５);like some strongly homoplastic Severalauthorsfavouraclade Phasmatodea+ apomorphies(e.g.,reductionoftarsomeres,lossofocelli Orthopterabasedonwingcharacters(e.g.,Haasand andwings)thesecharactersarenolongermentioned Kukalová-Peck,２００１;Willmann,２００３,２００５a),which here.Animportantpointtonoteisthatamongthe again cannotbeassessedin Mantophasmatodeaand “polyneopteran”taxas.l.thereareonlytwoforwhich Notoptera.Nonetheless,thecharactersareproblematic considerableevidenceexiststhattheymightbemore anywayduetoambiguousveinhomologies.Whether closelyrelatedtoAcercariaand/orEndopterygotathanto PhasmatodeaandOrthopterashare[１２９]anenlarged other“polyneopterans;”thesearetheDermapteraand praecostalfieldin theforewing(costaremotefrom theZorapteradiscussedbelow. anteriorwingmargin)isdifficulttoassess,because OnecharactermaysupportagroupPlecoptera+ extantPhasmatodealack the costa(Willmann,２００３ Orthoptera+ Dictyoptera+ Phasmatodea+ Derma- derivesthishypothesisfrom fossilPhasmatodeathat ptera+ Embioptera+ Notoptera(whileMantophasma- apparentlyhaveretainedthecosta;seealsoBéthouxand todeacannotbeassessedduetolackingexamination):In Nel,２００２andBéthoux,２００６). additiontotheusualincurrentostia,[１２５]thehearthas AcladePhasmatodea+ Orthoptera+ Dictyoptera alsoexcurrentostia.However,thesegmentaldistribu- issupportedby[１３０]aspecialapomorphicmusculature tionofthesevariesstrongly,andwhileinPlecopteraand ofthebasalampullaeoftheantennalvessels;thiswas Embiopteratheostiaareunpairedandmedioventral, foundinallinvestigatedDictyoptera(４species)and theyarepairedinDermaptera,Dictyoptera,Notoptera, Phasmatodea(onlyCarausius)butonlyinpartofthe Phasmatodea,andOrthoptera(Nutting,１９５１;Passetal., examinedOrthoptera(Passetal.,２００６:character８). ２００６;seeBarnhart,１９６１forabsenceinZygentoma). Thismusculaturewasalsoreportedtobeabsentfora AcladePlecoptera+ Orthoptera+ Dictyoptera+ mantophasmatodean(Baumetal.,２００７). Phasmatodea+Dermaptera+Notoptera+Mantophas- A group ofsimilar (but in detailuncertain) matodea(i.e.,underexclusionofEmbioptera)maybe composition is indicated by a rearrangement of indicated by two apomorphies,the firstofwhich, sclerotizationsinthecoxitesIX (valvifersIX)ofthe however,isnotapplicabletothewinglessNotopteraand female genitalia,which includes two apomorphies Mantophasmatodea.Thisis[１２６]theenlargedhindwing (Klass,２００３a:２０３ff).First,[１３１]amedianfusionofthe analfield,which in reposeisfoldedseveraltimes. anteriormostpartsofthetwocoxitesIX;itoccursin However,sincetheextenttowhichdifferentmainveins probablyallstudiedOrthoptera,Dictyoptera,Phasmato- contributetotheanalfieldvariesconsiderablyamongthe dea,andNotoptera(butalsoArchaeognatha,andnotin taxa(e.g.,HaasandKukalová-Peck,２００１;Béthoux, Mantophasmatodea).Second,[１３２]aspecifictransverse ２００５),itisdisputedwhetherthischaractercanbefully division ofcoxitesIX by which the medially fused homologizedamongtaxa.Inaddition,thiswingareahas partbecomesadiscrete,unpaired anteriorsclerite. often undergone strong secondary reduction (e.g., TransversedivisionsofcoxitesIXoccurindifferentways Isoptera, subgroups of Plecoptera), which further across Insecta;they can be distinguished by the reducestheconclusivenessofthischaracter.[１２７]Tarsal distributionofmuscleattachmentsoncoxiteIX(anterior euplantulaearefoundinalltaxalistedabove(e.g.,Beutel andposteriortergocoxalmuscles,coxogonapophyseal andGorb,２００１,２００６;Willmann,２００３,２００５a),butare muscles) and the articulation of coxite IX with (secondarily?)absentinseveralsubgroupsofthese. the gonangulum over the resulting sclerites.The Onlyasinglehighlydoubtfulwingcharactercan differentdivisions in Archaeognatha,in Dictyoptera be mentioned in favourofthe narrowergrouping and Orthoptera,and in Dermaptera,Acercaria,and Orthoptera+ Dictyoptera+ Phasmatodea+ Derma- Endopterygota(seebelow)canbedefinedbythese ptera(+ perhapsNotopteraandMantophasmatodea, criteria.Thespecificsubdivisionhereinquestionis which cannot be assessed):[１２８] the moderately unambiguouslypresentinmanyDictyoptera(butabsent increasedsclerotisationoftheforewings(tegmina).One inmanyothers)andOrthoptera-Ensifera(Klass,１９９８c); problemistheabsenceofforewingenforcementinbasal conditionsin Orthoptera-Caeliferaand Phasmatodea, Mantodea(Smart,１９５６)and itsweaknessin some however,are difficult to interpret.In Plecoptera, membersofDictyopteraandOrthoptera(Kristensen, Embioptera, and Zoraptera (and Ephemeroptera) １９７５:１２).Anotherproblem isthepresenceoftegmina characters[１３１]and[１３２]cannotbeassesseddueto HEXAPODPHYLOGENY:ACRITICALREVIEW １５

their lack of the ovipositor and related sclerite withrespectto,e.g.,thatofDictyoptera(Klass,１９９８a) differentiations. andthephasmidTimema(Tilgneretal.,１９９９).However, AcladeDictyoptera+ Notopteraissuggestedbya the presence ofa strongly simplified (Plecoptera, singlecharacter:[１３３]adiaphragm inthecercusthat Embioptera,andDermaptera)ormodified(Orthoptera) separatesthedistallyandproximallydirectedhemo- proventriculus(whichcouldbederivedfrom conditions lymphflows(Passetal.,２００６:character１１).Plecoptera asseeninNotopteraandMantophasmatodea)inother show the more plesiomorphic possession ofcercal neopteran lineages strongly limits the phylogenetic vessels,whileatleastMantophasmatodea,Embioptera, conclusiveness of this character. Notoptera and Phasmatodea,andOrthopteralack both vesselsand Mantophasmatodeasharesomeembryologicalfeatures, diaphragms.Ofcourse,theapplicationofthecharacterto i.e.,themannerofblastokinesisandthestructureofthe taxa with reduced cerciis somewhat problematic chorion(UchifuneandMachida,２００５:１１９f;Uchifuneet (comparecharacter[１０３]). al.,２００６). AcladePhasmatodea+Embiopteraissupportedby Ontheotherhand,thereisastrongsimilarity [１３４]thepresenceofanoperculum attheanteriorpole betweenMantophasmatodeaandDictyopterain[１４０] andasinglemicropyleontheventralsideoftheegg theconstructionoftherighthalfoftheasymmetrical (Jintsuetal.,２００７)(anoperculum isknownformany malegenitalia(Klassetal.,２００３:５７).Thispatternis Plecoptera,butprobablynotinthegroundpatternof absentinotherHexapoda(thoughare-examinationis thistaxon:Zwick,１９８０).An apomorphy unique to needed forNotopteraand Phasmatodea).A second PhasmatodeaandEmbiopterais[１３５]thepresenceofa charactersuggestingthisrelationshipconcerns[１４１] specialdorsaladductor muscle ofthe paraglossa; the walls ofthe antennalvessels,which only in probablyanadductorofthepraementum hasbecome MantophasmatodeaandDictyopterahaveatwo-layered subdividedbygaininganintermediateinsertion(Maki, basalpart,withapeculiarinnerlayeroftransporting １９３５:１９４;Rähle,１９７０:３０３);thedistalpartisthemuscle cells(Passetal.,２００６:Fig.１７). hereinquestion.However,onlyasinglespeciesper A more inclusive clade Mantophasmatodea + orderhasbeenexamined.Notopteracannotbeassessed Notoptera+ Dictyoptera+ Orthopteraissupportedby sinceneithertheundividednorthedividedmusclesare [１４２]thepresenceof“connectingbands”intheflagellum present(Rähle,１９７０:Table４).ForMantophasmatodea ofthespermatozoa(Dallaietal.,２００３,２００５). theplesiomorphicconditionhasbeenreported(Baumet A clade Mantophasmatodea + Phasmatodea is al.,２００７).ThecladePhasmatodea+ Embiopterais supported by the analysis of mitochondrialDNA congruentwith the molecularresultsofTerry and sequencesinCameronetal.(２００６b)andKjeretal. Whiting(２００５)andofKjeretal.(２００６). (２００６).Thetwotaxashare[１４３]aprojectingtransverse HaasandKukalová-Peck(２００１)proposeaclade scleritebehindthemalegenitalia(vomerresp.vomeroid Plecoptera+ Embiopterabasedonwingmorphology. inKlassetal.,２００２,２００３).However,differentpositional Thetwotaxaalsoshare[１３６]theunpairedexcurrent relationscontradictthehomologyofthesestructures ostiaoftheheart(Passetal.,２００６;comparecharacter (Klassetal.,２００２),anditremainstobetestedbya [１２５]),butitisnotclearwhethertheunpairedorthe comparativestudyincludingthemuscularconnections pairedcondition(foundinother“polyneopterans”)is whethersomepostabdominalscleriteinNotopteraisa plesiomorphicfortheseostia.Thelackofmalestyliand potentialhomologue.InbothMantophasmatodeaand oftheovipositor,andtarsomerereduction,thoughfound Phasmatodea[１４４]theeuplantulaearecoveredwith inmanyNeoptera,maybeviewedasadditionalsupport acanthae. In addition, Mantophasmatodea and the forthishypothesis. phasmatodeangenusTimema(sistertotheremaining Phasmatodea;e.g.,Bradler,２００５)share[１４５]characters Regarding Mantophasmatodea, two molecular ofthearolium,suchasitsenormouslylargesize(Klasset studies(TerryandWhiting,２００５;Kjeretal.,２００６)as al.,２００２)andaventralcoveragewithacanthae(Beutel wellasthemorphology-basedanalysisofBeuteland andGorb,２００８).(Thetwolattercharacterscannotbe Gorb (２００６)indicate a sistergroup relationship to assessedintaxalackingeuplantulaeandthearolium, Notoptera,whileforthiscladethereisvirtuallyno respectively.) supportfrom morphology.Theshared[１３７]absenceof Mantophasmatodea also share an apomorphic wingsand[１３８]absenceofocelli(thetwosynapomor- similarity with many Plecoptera:[１４６]a flattened phiesinBeutelandGorb,２００６)areweakarguments, processinthemiddleofthemalesubgenitalplate(Klass becausethesestructureshavebeenlostmanytimes etal.,２００２:Fig.２A),usedfordrummingonthesubstrate independently in Neopteraand may be functionally (EberhardandPicker,２００８).However,thiselementis correlated (Friedrich etal.,２００６).Notoptera and unlikelytobelongtothegroundpatternofPlecoptera(P. Mantophasmatodeaalsohave[１３９]asimilarproventricu- Zwick,pers.comm.). lus(Klassetal.,２００２),whichisprobablyapomorphic １６ K.-D.KLASS

ForDermapteraacloserelationshiptoAcercaria+ praementum could tentatively be added to thislist Endopterygota(ifthisisamonophylum)isindicatedby (BeutelandWeide,２００５).Charactersoftheovipositor [１４７]aspecialdivisionofcoxitesIXoftheovipositor cannotbeassessedinZorapteraduetobothitsreduction (Klass,２００３a:Figs.７７–７９;differentfromthedivisionin (Weidner,１９６９) and lack ofdetailed descriptions; character[１３２]).However,thiscannotbeassessedinthe characters[１２２]–[１２４]wouldthusallowforrelationships many dermapteran,acercarian,and endopterygotan (Acercaria + Zoraptera) + Endopterygota. (See subgroupsthathavetheovipositorreduced,andthe Yoshizawa,２００７forfurtherdiscussions.) sameistrueforZoraptera,Embioptera,andPlecoptera. Zoraptera+ Embiopterareceivessupportfrom [１４８] The occurrence ofmeroistic ovarioles with [１５８]the very heavy hind-tibialdepressormuscles branched cellclusters is consistentwith a group resultinginthickenedhindfemora(MinetandBourgoin, Dermaptera + Acercaria + Endopterygota,though １９８６),andfrom charactersofthehindwingarticulation conditionsinbasaldermapteransremainunknown,and (Yoshizawa,２００７;notapplicable to Notoptera and inbothAcercariaandEndopterygotaseveralreversalsto Mantophasmatodea,andnotexaminedinOrthoptera): panoisticovarioles(“neopanoistic”)mustbeassumed [１５９]theenlargedtegula,[１６０]thedetachedposterior (Kristensen,１９９９;Heming,２００３:５４f).Inthemeroistic notalwingprocess(seeYoshizawa,２００７fordifferences ovarioles of Collembola, Diplura-Campodeina, and tothesimilarconditioninsomeEndopterygota),[１６１] Ephemeroptera,cellclustersarelinear(e.g.,Heming, theconnectionofthelatterwiththe１staxillary,[１６２]a ２００３:４１f,Fig.２.９.). specialsubdivisionofthebasiradialsclerite,and[１６３]a Apomorphies indicating a clade Dictyoptera + farposteriorlylocatedattachmentofaventralwing Dermapteraare[１４９]thelargefemalesubgenitalplate ligament to the ２nd axillary. Yoshizawa (２００７) formedbythecoxosterniteofabdominalsegmentVII additionally mentions [１６４]an enlargementofthe (Klass,１９９８c,２００３a),and[１５０]thefusionofabdominal anteriorpartofthe１staxillary,butthisappearsdoubtful ganglion７totheterminalganglion(neuromeres８–１１; duetothehighlyvariableproportionsandpositional Klass,２００１a;the latterapomorphy also appliesto relationshipsofthispartofthe１staxillaryacrossthe ZorapteraandAcercariawiththeirextensivelyfused neopterantaxa.Furthersynapomorphiesproposedfor abdominalganglia).Charactersofthewingsandofthe ZorapteraandEmbioptera,suchassubsociality,reduced exoskeleton and musculature of the wing-bearing numberofantennalflagellomeres,andothers,aretoo segmentsmayconfirm thisrelationship(Boudreaux, unspecificorhomoplasticastoyieldmuch support １９７９;HaasandKukalová-Peck,２００１:４８４).Thisincludes (BeutelandWeide,２００５:１３３).Thereportofcharacter [１５１]thereductionofthedorsallongitudinalmuscles [１６０]foraphasmatodean(Yoshizawa,２００７)indicatesa andtheirmainattachmentsites(phragmata),andofthe clade Phasmatodea + (Embioptera + Zoraptera). tergosternalmuscles.WhileusuallyinPterygotathese GrimaldiandEngel(２００５)assumeacladePlecoptera+ musclesstronglycontributetothedown-andupstroke, (Embioptera+ Zoraptera),buttheirargumentsare respectively, the downstroke in Dictyoptera and simplereductions(tarsomeres,ovipositor,malestyli) Dermapteraiseffectuatedbymusclesofthebasalare foundinmanyneopterans. and subalare,and the upstroke isaccomplished by HaasandKukalová-Peck(２００１)placeZorapteraina tergopleuraland tergocoxalmuscles(see also Kris- group also including Dermaptera, Notoptera, and tensen,１９８１). Dictyoptera,but regard this as poorly supported. RelationshipsbetweenZorapteraandDictyopterahave The Zoraptera have been assigned to various variouslybeensuggestedbasedonzorapteran-isopteran positionsin the system ofNeoptera,butonly two similaritiessuch as[１６５]wing shedding and [１６６] hypothesesaresupportedconsiderably(seeEngeland presence ofdifferentmorphs.These apomorphies, Grimaldi,２０００,２００２;GrimaldiandEngel,２００５;Beutel however,areinconflictwithdictyopteranautapomor- andWeide,２００５;Yoshizawa,２００７):zorapteran-acer- phies(Klass,２００３b),asIsopteranow are strongly carianandzorapteran-embiopteranrelationships. supportedtobesubordinatewithin Blattaria(Klass, Zoraptera+Acercaria(seeHennig,１９６９,１９８１)has ２００１b;Lo,２００３;TerryandWhiting,２００５;Klassand beenobtainedintheanalysisbyBeutelandGorb(２００６) Meier,２００６;Kjeretal.,２００６;Pellensetal.,２００７;Loet basedon[１５２]anextensivefusionoftheabdominal al.,２００７;Inwardetal.,２００７;Wareetal.,２００８).Further ganglia,[１５３]thecibariumformingasuckingpump,and charactersthathadbeenproposedtosupportzorapteran- [１５４]theslender,elongatemaxillarylaciniaethatlack dictyopteranrelationshipsarerejectedinBeuteland mesallydirectedsetae.Willmann(２００５a)additionally Weide(２００５:１３３). mentions[１５５]theareolapostica,aspecialconfiguration MolecularevidenceontheplacementofZoraptera inthewingvenationformedbyaforkofthecubitus issparse,andthehighlyderivedrDNAsequencespose anterior.[１５６]The large and complex clypeobuccal analyticalproblems (branchlengtheffects:Yoshizawa, muscle and [１５７]a median internalridge on the ２００７).Zorapterahavebeenobtainedeitherassisterto HEXAPODPHYLOGENY:ACRITICALREVIEW １７

Dermaptera(highsupportinTerryandWhiting,２００５)or meansthatphylogeneticworkonbasalhexapodscan ofDictyoptera(YoshizawaandJohnson,２００５).Thereis onlybeconvincingifembeddedinphylogeneticworkon nomorphologicalevidenceforZoraptera+Dermaptera; mandibulatearthropods,i.e.,itmustcurrentlyconsider TerryandWhiting(２００５)mentiontheone-segmented muchofthemorphologicalandgeneticdiversityfound cerci,buttherearefossilrepresentativesofbothtaxa acrossmyriapodsandcrustaceans.Thisalsorequires thathavemorecercomeres(seeWillmann,２００３,２００５a extensiverenewedevaluationofmanymorphological andYoshizawa,２００７). charactersystemsaswellasaclosecollaborationamong researchersspecializedonthemajormandibulatetaxa. ７.Conclusions Inrecentyearsanumberofmorphologicalcharacter Acknowledgments:Ithank my friend Ryuichiro systems were intensely studied in many taxa.The Machida(SugadairaMontaneResearchCenter,Univer- evidencefromoldandnewlyfoundcharacterswasaptly sity of Tsukuba, Japan) and other members of discussed in specialized contributions,and analyses theArthropodan EmbryologicalSocietyofJapan for basedonlargecharactermatriceswereconducted.DNA invitation to contribute a presentation on hexapod sequencedatawereacquiredfornumeroushexapod phylogeny at the ４３rd Annual Meeting of the species(thoughwithastrongfocusonahandfulof ArthropodanEmbryologicalSocietyofJapan(July４–６, markers),andmethodsfortheanalysisofsuchdatawere ２００７)andtowritethisarticle.Theprojectandvisitto greatlyimproved.However,characterincongruencehas the meeting were supported by a grantfrom the sofargrowntothesameextentastheamountofdata, InternationalCooperativeResearchProjectUniversity andtherehasbeenhardlyanyimprovementwithregard ofTsukuba(Invitation)(２００７). totheunresolvedpartsofhexapodphylogeny.Yet,onlya smallfractionofthepotentiallyusabledatahasbeen References made available by now forpurposes ofphylogeny Abascal,F.,D.Posada,R.D.KnightandR.Zadoya(２００６)Parallelevolutionof reconstruction,andthisconcernsbothmolecularand thegeneticcodeinarthropodmitochondrialgenomes.PLosBiology,４ (５),e１２７doi:１０.１３７１/journal.pbio.００４０１２７. morphologicaldata. 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