Description of the larva ofTrineuragrion percostaleRis (Odonata: Megapodagrionidae) with a key to the larvae of New Caledonian genera of Megapodagrionidae

2012·0.24 MB·

by  Milen G. Marinov

InternationalJournalofOdonatology
Vol.15,No.3,September2012,241–248
Description of the larva of Trineuragrion percostale Ris
(Odonata: Megapodagrionidae) with a key to the larvae
of New Caledonian genera of Megapodagrionidae
MilenG.Marinov*
SchoolofBiologicalSciences,UniversityofCanterbury,PrivateBag4800,Christchurch8140,
NewZealand
(Received15February2012;finalversionreceived23July2012)
ThelarvaofTrineuragrionpercostaleisdescribedandillustratedbasedonanexuviacollectedwiththe
teneralfemale.Fourmoreexuviaesampledwithoutimaginesareaddedforcomparisonanddiscussion
ofmorphologicalvariations.Thisisthefirsttimethelarvahasbeenassociatedwiththecorrectspecies,
althoughthelarvaldescriptionwasgivenearlier.LieftinckincludeditinhisanalysisofNewCaledo-
nianOdonatalarvalfaunaunderthenameCaledargiolestesuniseries(bysupposition).Variationsinthe
morphologicalfeaturesbetweenLieftinck’sspecimensandthosereportedherearediscussed.Thekeymor-
phologicalfeaturesthatdifferentiatelarvaofT.percostalefromotherMegapodagrionidaeinthecountry
areindicated.
Keywords: Odonata;dragonfly;larva;Megapodagrionidae;Trineuragrion;NewCaledonia
Introduction
TheOdonataofNewCaledoniaarefairlywellknownbasedonfaunisticandtaxonomicinvestiga-
tionsofimagines.Larvaehavebeenunderstudied,however(Lieftinck,1971,1976;LippittWilley,
1955;Starmühlner,1968;Winstanley,1983,1984).Lieftinck(1976)providedtheonlyidentifi-
cation keys for larvae. They feature two of the endemic New Caledonian groups by including
representativesofIsostictaandSynthemisgenera.Inthesamepaper,detailedlarvaldescriptions
arealsoprovidedforotherendemicspecies,including,bysupposition,Caledagriolestesuniseries
(Ris,1915)andothermegapodagionids.Inalaterstudy,Winstanley(1983)collectedandreared
larvae from New Caledonia which enabled him to correctly associate the larvae to adults for
C.uniseriesandSynthemismirandaSelys,1871.Caledagriolestesuniserieswasfoundtobethe
uniqueunidentifiedterrestriallarvaoriginallydescribedbyLippittWilley(1955)andcommented
uponbyLieftinck(1976).ThereforethedescriptionbysuppositionofC.uniseriesinLieftinck
(1976)wasnotofthatspecies.Winstanley(1983)leftthecorrectspeciesaffiliationofthelatteran
openissue.However,whiledescribingthelarvaebysupposition,Lieftinck(1976)madeavaluable
remark.ThefinaldecisiontorelatetheunknownlarvaetoC.uniserieswasinfluencedbywing
characters: “... length–breadth ratio of the wings and the shape of the pterostigma.” However,
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242 M.G.Marinov
healsoemphasisedthatwingvenationwasclosetothatofTrineuragrionpercostaleRis,1915.
De Marmels (2001) suggested that: “the larva of Trineuragrion is probably, and by exclusion,
the one identified by Lieftinck (1976) as ‘Caledargiolestes uniseries”’. Finally, Kalkman et al.
(2010b)includedthelarvaofT.percostaleintheiranalysisofthelarvalgillsofmegapodagrionids
basedoncollectedbutundescribedmaterial,depositedattheCambridgeUniversityMuseumof
Zoology,UK.Currently,however,nocleardescriptionintheliteratureexiststounambiguously
associatelarvaeofT.percostaletotheimago.
Recently a teneral T. percostale was discovered with its exuvia from a stream in NE New
Caledonia,andthelarvaisdescribedandillustratedherein.Acomparisonismadewithfourother
exuviaecollectedduringthecourseofthisstudy,andwiththedescriptionofthelarvaattributed
toC.uniseriesbyLieftinck(1976).Importantdiagnosticfeaturesarehighlighted.
Materialandmethods
Thematerialwascollectedduringthe2010RapidAssessmentProgram(RAP),MtPanié,New
Caledonia.OnefemaleimagowithitsexuviawasdiscoveredinPwéKédivinCreekon21October.
Bothimagoandexuviawerestoredin90%ethanol.FourotherexuviaeweresampledattheWewec
Riveron15OctoberandidentifiedasT.percostalebasedonthediagnosticfeaturesestablished
intheoriginalfemaleexuvia.Variationsinthebodysizeandstructureswerealsorecorded.
Pictures of the female exuvia were taken with aid of Leica M125 stereomicroscope using
Leica Application Suite V3.8. The drawings used in the current description were made with
AdobePhotoshopCS4Extendedsoftwarefromtheoriginalphotos.Allmorphologicalfeatures
were traced with Wacom Bamboo MTE-450A tablet. Measurements (in mm) were made with
calibrated ocular micrometer as follows: total length, dorsally from the anteriormost margin of
labrumtothetipofthegills;headwidth,acrossthecompoundeyes;pronotum,dorsallyacrossthe
cornersoftheshield(cf.Diagnosisbelow);femora,alongthemidlineoftheexternalsurface;gills,
dorsally from where attached to the abdomen to the tip (termination of central tracheal trunk);
wingsheaths,longitudinallyofthehindrightwing.S1–S10=abdominalsegments1to10.
Description
Specimensexamined
An exuvia with its associated female imago, Pwé Kédivin creek crossing the road Hiénghène-
Pouéboabout10.4kmNWofHiénghène(20◦37(cid:3)57(cid:3)(cid:3)S,164◦51(cid:3)52(cid:3)(cid:3)E;40masl,21October2010);
fourexuviae,WewecRiverabout880mdownstreamfromtheRAP-NewCaledoniaRefuge2site
(20◦35(cid:3)30(cid:3)(cid:3)S,164◦44(cid:3)17(cid:3)(cid:3)E;265masl,15October2010).
Diagnosis
GeneralappearanceandcolourpatternasinFigure1a,b.Bodyuniformlylight-brownandcovered
withshorthairs.Gillsflat,arrangedhorizontally,thustypicalofwhatareconsideredtobeFan
megapodagrionids(Kalkmanetal.,2010b).
Head
Roughly pentagonal, eyes smoothly aligned with postocular lobes and forehead. Dorsal area
mostlyflat,raisedatthelevelofpostocularlobesandcurvedslightlydownwardstowardslabrum.
Thelarvaof Trineuragrionpercostale 243
Figure 1. Trineuragrionpercostaleexuvia–(a)dorsalview;(b)ventralview;(c)prementum;(d)labialpalp;(e)gills
dorsalview;(f)gillsventralview.Figuresnottoscale.
Group of three light spots on vertex in occipital area between eyes. Postocular lobes evenly
rounded.Antennasixsegmented;scapestout(width:length=1:1.36);pedicellarge,butthinner
thanscape(width:length=1:2.17);segmentsofflagellumequalinshape,moreslenderthanfirst
twosegmentsandalmostthesamelengthasscape+pedicel;shorthairsdenselycoverfirsttwo
segments. Prementum (Figure 1c) of moderate length, flat, reaching midway between first and
secondcoxae(differencesamongindividualsislikely);laterallywithveryslightlybulgeatthe
middle, constricted proximally and ending with two well-expressed angular projections; distal
enddeeplyincisedwithtwoserratedlobesinmid-sectionbearingshortlightseta-liketubercules
ineachindentation.Labialpalps(Figure1d)wideandstout,elongateddistallytosharptooth-like
projection.Movablehooklargeandsharppointed.Prementalandlabialsetaeabsent.
Thorax
Allthreesegmentsofsimilarlengthbutdifferentshape(dorsalview).Prothoraxlarge,flat,shield-
shaped; largely rounded posteriorly and nearly straight anteriorly; width anterior :posterior =
1:1.36.Mesothoraxwithroundandsmoothlateraledges.Metathoraxtaperingposteriorly.Legs
relativelylong.Femorairregularlycylindricaltodome-shapedwithlongitudinalmid-carinador-
sallyandtworibs(mostpronouncedonhindfemora)ventrally.Tibiaeslightlynarrowerandlonger
than femora with up to 4 longitudinal ribs each and short hairs developed alongside them.All
244 M.G.Marinov
tarsibutone(middlerightleg)three-segmented;twoclawsonalltarsi,simplewithnoextrateeth
exceptonmiddlerightleg.Hindlegssurpasstipofabdomenwhenfullyextended.Windsheaths
slightlybeyondanteriorendofS4(differencesamongindividualsislikely).
Abdomen
Relativelyshort,equalinlengthtohead+thorax.S1–S4appearlaterallyexpanded,nearly1.36
timeswiderthanS5–S10(differencesamongindividualsislikely).S9withoneventrolateralspine
in each side (one smaller supplementary spine anteriorly on left side). S10 with 5 ventroapical
spinesateachside.Gills(Figure1e,f)largeandwidelyoval;proximalendsthickerandelevated,
almost completely aligned transversely for all three gills; rest of gill surface membranous with
fine spiny tubercules. Median lamella covers about 4/5 of each lateral lamella. Median lamella
leaf-likeandovalinshapewithlength:widthratio=1:1.40;shortspinesdevelopedalong3/4of
eachlateraledge,becominglongerandlessdensetowardstipofgill;shorthairs,aslongasthe
spines,developedabouthalfwayfromtipofgillandbecomingtwiceaslongasspinesatdistalend;
centraltrachealtrunkverylargeandstoutwithweakbranchesextendingperpendicularlytowards
lateraledges.Laterallamellaewithsimilararrangementsofspines,hairsandtrachealtrunkwith
branches; they differ in having: (a) proximal elevation with immediate concavity continuing in
themembranousarea;(b)terminalhairsalmostaslongasspines,stifferandformingbrush-like
tipsofongills;(c)lateraltrachealbranchesmorenumerousandleavingcentraltrunkatanangle.
Measurements(mm)
Total length 15.3 (including gills); head width 3.3; pronotum dorsal width 2.2; femora length:
fore 2, middle 2.2, hind 3.1; gills length: median lamella 4.2, lateral lamellae 2; wing sheaths
length4.
Variations
Thefourotherexuviae(2(cid:2)(cid:2)and2(cid:3)(cid:3))identifiedasT.percostaledifferslightlyfromthedescrip-
tiongivenabove.Masksreachingbasesofmiddlecoxae.Wingsheathsextendingtoposteriorend
of S4 in three exuviae and to middle of S4 in one male exuvia. First four abdominal segments
not expanded laterally. S5–10 covered dorsally with short hairs forming dense fringes weakly
developedinS5andS10,butgoingwellbeyondthedistalendsofS6–9.Onemaleexuviawith
supplementaryventrolateralspineononesideofS8.Gillswereexaminedingreaterdetailonone
maleexuviaonlyasgillswereabsentintheotherspecimens(1(cid:2)and1(cid:3))orhaddriedoutina
way that made the precise measurements impossible (1(cid:3)). Gills covered with dense, very long
hairs on the elevated proximal area.Terminal hairs nearly three times as long as the spines on
thetipofthegills.Althoughtheshapeofthegillsoftheadditionalfemaleexuviacouldnotbe
examined, some other features could be compared with the larva description given above.The
gillsurfaceareaappearedtobecoveredwithadenserarrayofmuchlongerhairs,predominantly
ontheelevatedproximalpartofthemedianlamella.Longhairsalsocoveredthecentraltracheal
trunkstartingapproximately2/3fromthetip.Fringehairsresembledthoseonthemaleexuvia.
Measurements: body length (without gills) 11.6–12.7; head width 3.3–3.7; pronotum dorsal
width2.1–2.7;femoralength:fore2.1–2.2,middle2.6–2.9,hind3.4–3.8;wingsheaths4.2–4.6.
Gillsmoreelongatedwithlength:widthratio=1:1.53(measuredinmedianlamellaonly).
Thelarvaof Trineuragrionpercostale 245
Habitatpreferences
T. percostale is common along forest-edge streams (Davies, 2002). Marinov et al. (in press)
describeitasatypicalinhabitantofmoderatesizeriversofabout5–6mwide,althoughitalso
occursinwiderrivers.Riverbanksweredenselyvegetatedwiththetreecanopyover70%.Fallen
treetrunksandbranchesinthemiddlecourseoftheriverwerefoundtobeofgreatimportancefor
matingandovipositing,andonewasthelocationinwhichthefemalewiththeexuviadescribed
herewasfound.Theotherfourexuviaewerecollectedonprotrudingbouldersabout1mfromthe
bankina20mwide,shallowrockyriver.
PreliminarykeytothelarvaeoftheNewCaledoniangeneraofMegapodagrionidae
The correct association of larva to imago of T. percostale completes the descriptions of the
larvae of the four Megapodagrionidae genera known to inhabit New Caledonia. Larvae of two
species remain undiscovered (Table 1) and make it impossible to compile a complete species
identification key for the larvae. However, the available diagnostic characteristics for the four
genera(summarisedinLieftinck,1976),incombinationwiththedistributionrecordsandcertain
suppositions,mayfacilitateanear-preciseidentification.Thefirstpreliminarylarvaeidentification
keytotheNewCaledonianMegapodagrionidaegeneraissuggestedbelow.Thekeyislargelybased
onthepublisheddescriptionsandfiguresinLieftinck(1976)andthusrequiresfurtherverification
because no other larval material was checked during this study apart from what is reported
above.Thekeyisaccompaniedbytheassumptionsthatoneshouldconsiderwhenidentifyingthe
specimensatthisstageofknowledgeuponlocalOdonatafauna.
1. Prementum with medial incision of distal margin a rounded V-shape, not slit-like basally
(Figure2a)........................................................................2
1(cid:3). Prementumwithmedialincisionofdistalmarginanarrowslitformuchofitslength,nearly
closedbasally(Figure2b)...........................................................3
2. Labialpalpwithteethatthetip(Figure 3a);scapeandpedicelelongatedwithscapenearly
threetimesaslongaswide;maskreachesthebasesofthefirstcoxae..........Argiolestes
Table 1. NewCaledonianspeciesofMegapodagrionidaeforwhichthelarvaisdescribed(basedonKalkmanetal.,
2010bandthispaper).
Species Reference Comment
Argiolestesochraceus(Montrousier,1864) Lieftinck(1976)
CaledargiolestesjaniceaeLieftinck,1975 Nolarvadescribed
Caledargiolestesuniseries(Ris,1915) Willey(1955),Lieftinck(1976) FormoredetailsseeTable1in
Kalkmanetal.(2010b)
CaledopteryxmaculataWinstanley& Lieftinck(1976) FormoredetailsseeTable1in
Davies,1982 Kalkmanetal.(2010b)
Caledopteryxsarasini(Ris,1915) Nolarvadescribed
TrineuragrionpercostaleRis,1915 Lieftinck(1976);thispaper
Figure 2. Comparisonbetweentheincisionsofthedistalpartoftheprementumin:(a)Agriolestes;and(b)Caledargi-
olestes.DrawingsafterLieftinck(1976);nottoscale.
246 M.G.Marinov
Figure 3. Comparisonbetweenthelabialpalpsof:(a)Argiolestes;and(b)Trineuragrion.DrawingsofArgiolestesafter
Lieftinck(1976),thoseofTrineuragrionoriginal;nottoscale.
Figure 4. Comparisonincrosssectionbetweenthegillsof:(a)Caledopteryx;and(b)Caledargiolestes.Drawingsafter
Lieftinck(1976);nottoscale.
2(cid:3). Labialpalpwithoutteethatthetip(Figure3b);scapeandpedicelstoutwithscapelessthan
1.5timesaslongaswide;maskreachesthebasesofmiddlecoxae..........Trineuragrion
3. Gillsflatincrosssection,onlycentraltrachealtrunkconspicuous(Figure4a);larvaegenerally
hairless................................................................Caledopteryx
3(cid:3). Gills swollen in cross section mostly at the central tracheal trunk, but also in the lateral
expansions(Figure4b);almosttheentirelarvacoveredindensehairs.....Caledargiolestes
Notesonthekey
Argiolestes currently includes 48 species found on New Caledonia, through much of western
Melanesia,andSulawesiandLuzon(Kalkmanetal.,2010a).A.ochraceus(Montrousier,1864)
isthesolerepresentativeofthegenusandisendemictoNewCaledonia.Davies(2002)foundit
quitecommonthroughoutthecountry.
Trineuragrion is a monotypic genus, with T. percostale Ris, 1915 being widespread in New
Caledonia(Davies,2002)andalsoknownfromtheRepublicofVanuatu(Kimmins,1936).
Caledopteryxincludestwospecies,bothendemictoNewCaledonia.C.maculataWinstanley
&Davies,1982isconfinedtothesouthwithitscurrentlypublisheddistributionrangeasfarnorth
as the road from Boulouparis toThio or perhaps theWest to East road from Bourail to Canala
(Davies, 2002). C. sarasini (Ris, 1915) is only reported north of that border. Lieftinck (1976)
Thelarvaof Trineuragrionpercostale 247
describedthesupposedlarvaofC.sarasinibeforethedescriptionofC.maculata,but,according
toWinstanley&Davies(1982),Lieftinck’sdescriptionwasbasedonlarvadiscoveredinalocality
whereatpresentonlyC.maculataisknown.ThusLieftinck(1976)probablydescribedthelarva
ofC.maculata(Kalkmanetal.,2010b),leadingtotheassumptionthatlarvaofC.sarasiniisstill
unknown(Table1).
Caledargiolestes also includes only two New Caledonia endemics. The key to the genera is
basedonthedescriptionofthelarvaoriginallypublishedinLippittWilley(1955)asanunidentified
larvaandredescribedinLieftinck(1976)as“Genusetspeciesincert”.Itscorrectaffiliationwas
clarified by Winstanley (1983), who claimed it as belonging to C. uniseries (Ris, 1915) (all
commented upon in Kalkman et al., 2010b). The other species from the genus, C. janiceae
Lieftinck,1975,appearstobeanearallytoC.uniseriesandprobablytheirlarvaearesimilar.The
larvaofC.janiceaeisnotdescribedyet(Table1),butprobablyitwillkeyoutinCaledargiolestes
andcouldbeidentifiedbysupposition.C.janiceaeisknownfromonelocalityonly,MtPouédihi
(Davies,2002;Lieftinck,1975),whileC.uniseriesiscommonandwidespread(Davies,2002).
Discussion
Althoughreportedhereasforthefirsttime,theactualdescriptionofthelarvaofT.percostalewas
made earlier. Lieftinck (1976) included a description in his detailed study on New Caledonian
larvae under the name Caledargiolestes uniseries (by supposition). His judgement was made
uponthreefullygrownlarvaewhichhehaddissectedinordertoexaminethewingvenation(see
above). However, the description of the larva agrees in most of the characters with the female
T. percostale presented here. The identification features in full congruence (which were also
foundtobediagnosticforT.percostale)are:(a)shapeofthelabiumandallitsparts(tipsoflabial
palps, shape of movable hook, incision of the median lobe with fine dentition and short hairs,
and posterolateral corners); (b) shape of the antenna; and (c) the total body size.Although not
illustratedherethemandiblespresentedinLieftinck(1976,p.176,fig.28)arealsoidenticalwith
theexuviaexaminedduringthecurrentstudy.Theonlydifferenceobservedwasintheshapeand
hairinessofthegills.
Lieftinck(1976)’sdrawingsdepictamalespecimen.Thegillsappeartobelongerandtohave
longerhairsthanthefemaledescribedhere.Similarcharacterswereestablishedinthemaleexuvia
examinedhere(seeVariations).Giventheresemblanceinotherfeatures,thedisparityinthegills’
characters could be attributed to sex-related differences, although at present such statement is
highly speculative given the low number of exuviae examined during the study. Moreover, sex
discriminationinlarvalgillsisnottypicalofZygoptera(R.Seidenbusch,personalcommunication,
August,2011).Othervariationsamongthefiveexuviaewerelikelytobeeithernaturaloraresult
ofthepreservationmethodoftheoriginalfemaleexuvia.Theswellingofthefirstfourabdominal
segmentsandtheextentofthemaskareconsistentwiththeeffectofethanol.Theoverallhairiness
ofthefemaleexuviafromtheoriginaldescriptionwasfoundtobelessthanthemaleexuvia,but
thisisunlikelytobeattributabletointersexualdifferencesbecausethesecondfemaleexuviahad
gillscoveredinasimilarpatternasthemales.Whiletheethanolcouldberesponsiblefortheloss
ofhairsonsomebodyparts,theshapeofthegillsseemwelloutlinedanddoesnotappeartobe
influencedbythepreservationmethod.However,furthermaterialisneededtotestthevariations
intheshapeofthegillsinT.percostale.
Acknowledgements
Ithankourlocalguidesforprovidinguswiththebestpossibleassistanceinthefield,andforkindlyhostingusontheirland.
Myspecialgratitudegoestotheorganisersofthe2010NewCaledoniaRAP,particularlytoFrancoisTronandRomain
248 M.G.Marinov
FranquetbutalsotothewholeConservationInternational-NewCaledoniastaff,theirpartnerorganisationDayuBiik,and
J.J.CassanofProvinceNord.IamgratefulalsotoHamishGreigforlinguistichelpaswellasGüntherTeischinger,Jürg
DeMarmels,MikeMay,RichardSeidenbuschandVincentKalkmanwhoassistedwiththeliteraturereviewandcritique
duringthepreparationofthemanuscript.
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