The maxillo-labial complex of Sparasion ( Hymenoptera , Platygastroidea )

Hymenopterans have evolved a rich array of morphological diversity within the maxillo-labial complex. Although the character system has been extensively studied and its phylogenetic implications revealed in large hymenopterans, e.g. in Aculeata, it remains comparatively understudied in parasitoid wasps. Reductions of character systems due to the small body size in microhymenoptera make it difficult to establish homology and limits the interoperability of morphological data. We describe here the maxillo-labial complex of an ancestral platygastroid lineage, Sparasion, and provide an ontology-based model of the anatomical concepts related to the maxillo-labial complex (MLC) of Hymenoptera. The possible functions and putative evolutionary relevance of some anatomical structures of the MLC in Sparasion are discussed. Anatomical structures are visualized with Confocal Laser Scanning Microscopy.


Introduction
Despite relatively recent efforts (e.g., Austin andField 1997, Murphy et al. 2007), the phylogeny of Platygastroidea remains largely unresolved, as such insights from previously unexplored character systems have the potential to make important contributions to our understanding of the groups evolution.As Platygastroidea are usually reduced in body size, the number of informative characters is limited to those anatomical complexes that cannot be simplified without negatively affecting the wasps' survival.In the case of Platygastroidea two character systems seem to match this requirement: the ovipositor apparatus (Austin 1983, Field and Austin 1994, Austin and Field 1997) and the mouthparts including the maxillo-labial complex.While the former is crucial for the piercing the chorion of host egg and laying the wasp's own eggs, the second structure is vital to the process of feeding.Very little is known about the feeding behavior and diet of adult platygastroids.Some species, e.g., the phoretic mantid egg parasitoid Mantibaria, feed also on their hosts' body fluids (Clausen 1976).
Due to the extreme diversity of Hymenoptera foraging strategies homologizing mouthpart structures within the order is a challenging task.Other than palpal formulae (Kieffer 1926, Masner 1976, Kononova and Kozlov 2001) and a relatively superficial survey of the maxillo-labial complex (MLC) in some genera of platygastroids (Popovici and Fusu 2006) data on MLC morphology in platygastroids have never been published.
Sparasion is a fairly speciose genus, with 141 valid species (Johnson 1992, Johnson et al. 2008).These wasps are widespread in Eurasia, Africa, and temperate North America (Johnson et al. 2008), and, as far as is known, these species are egg-parasitoids of Tettigoniinae (Orthoptera: Tettigoniidae) (Johnson et al. 2008).Based on the latest phylogenetic analyses, Sparasion is part of a small lineage that is sister to either the vast majority of Scelionidae sensu Haliday 1839 (Murphy et al. 2007) or Platygastridae sensu stricto (Austin and Field 1997).Species in this lineage typically exhibit ancestral morphological states (Murphy et al. 2007, Austin andField 1997), which should facilitate homologization of mouthparts with other hymenopterans.Sparasion are also relatively large species, with less anatomical simplification, which makes them more suitable for dissection and observation.

Material and methods
We examined 34 specimens of 10 Sparasion species (Appendix 1).All specimens were stored in 70% ethanol prior to dissection.Card-mounted voucher specimens are deposited in the Insect Collection of University "Al.I.Cuza" Faculty of Biology, Iasi, Romania (OPPC), in the C. A. Triplehorn Insect Collection, Ohio State University, Columbus, OH, USA (OSUC) and in the Frost Entomological Museum, Pennsylvania State University, State College, PA, USA (PSUC).
We followed the protocols of Prinsloo (1980) for specimen preparation.The head was boiled in 10% phenol in lactic acid for 30 minutes and rinsed in distilled water.The MLC were separated from the cranium using forceps (Dumont #5) and insect pins (size 2), then were transferred into 10% NaOH and macerated for 30 minutes, than transferred and rinsed in glacial acetic acid for 10 minutes.Clear and neutralized MLC specimens were dehydrated using ethanol series (70%, 96%, and 100% alcohol; 30 min each) and transferred to a clove oil droplet on concave microscope slide.The labium was separated from the right and left maxillae and mounted separately in Canada balsam medium.MLC specimens were examined under Euromex GE 3045 microscope (400×-1000×).Line drawings were made using Reichart drawing tube attached to the same microscope.Photos were taken using a Leica DFC-500 camera mounted on a Leica M 205A stereomicroscope.
CLSM images were taken on glycerin-stored specimens with Zeiss LSM 710 Confocal Microscope.For visualizing anatomical structures we used excitation wavelength of 488 and emission wavelength of 510-680 nm, detected using two channels visualized separately using two pseudocolors (510-580 nm=green; 580-680 nm=red).For visualizing resilin we used excitation wavelength of 405 nm and emission wavelength of 510-680 nm detected using one channel visualized with blue pseudocolor.
For Scanning Electron Microscopy (SEM) specimens were dried using hexamethyldisilazane (HMDS, Brown 1993), mounted on double adhesive tape and coated with gold.SEM images were taken using VEGA T SCAN SEM.

Maxilla (integument)
The cardo (cd: Fig. 1A-B) is triangular.The submedial maxillary process of the hypostoma (hys: Fig 1A) inserts submedially on the proximal part of the cardo (caf: Fig. 1B).The mediodistal cardinal ridge, laterodistal cardinal ridge and basal cardinal ridge are present (lcr, mcr, bcr: Fig. 1D) and the inner and outer cardinal processes are absent.The cardo lays almost parallel to the external surface of the hypostoma and is largely obscured by it even if the maxillo-labial complex is fully protracted (Figs 1A, cd: 4A).The conjunctiva connecting the cardo to the rest of the maxillo-labial complex is resilin rich along the stipitocardinal hinge (sch: Fig. 1C).
The stipes is triangular in cross section distally.The posterior stipital wall of the stipes bears the posterior stipital sclerite (pss: Figs 1A, C, 2B, C), while the partly sclerotised medial wall and the convex and membranous anterolateral wall (conj: Fig. 1B) bears the galeo-lacinial complex (Fig. 2A, B, D; gal-lac: Fig. 1B, C).The posterior stipital sclerite is triangular in posterior view, and is margined by the principal carina of stipes (pcs: Figs 1A-C, 3A), which is less rigid and melanized than other regions of the sclerite and is the most developed medially and distolaterally.The principal carina of stipes is equipped distolaterally with the marginal fringe of the stipes (mfs: Figs 1A-C, 2B, C) composed of occasionally branched spines.The extent of the principal carina of the stipes on the distolateral margin is variable in different Sparasion species (compare pcs of Fig. 1A with that of Fig. 1B) but it always overlaps the proximomedial surface of the mandible (md: Fig. 1A).The median part of principal carina of the stipes is divided into the proximomedian stipital flange (pmf: Figs 1B, C, 2A) and the distomedial stipital flange (dmf: Figs 1C, 2A, B, C).The proximal part of the distomedial stipital flange posteriorly overlaps the distal part of the proximomedial stipital flange (pmf, dmf: Fig. 1C).The stipes articulates with the postmentum (psm: Figs 1C, 2C) and the distal prementum (pmn: Fig. 1A, C) along the proximomedial stipital flange and with the proximal prementum via the distomedial stipital flange.The medial stipital groove (msg: Figs 1A, 2B) extends medially along the proximomedial stipital flange and distomedial stipital flange and accommodates the first sclerite of the maxillary palp (mpalp: Fig. 1A, C, 3D, E) when it is adpressed against the stipes.The posterior stipital sclerite is glabrous, except a for few, elongate, mechanosensory hairs (msh: Figs 1C, 2B) just proximal of the base of maxillary palp and along the distolateral margin of the stipes abutting the hypostoma.The distal part of the posterior stipital sclerite is equipped with numerous campaniform sensilla (cps: Fig. 2C), which are visible only with transmitted light.
The galeo-lacinial complex has four sclerites and two marginal lobes.The proximal, inverted T-shaped lacinial lever (bls: Fig. 2A, B) and the distal, narrow basal galeal sclerite (bgs: Fig. 2B, D) are situated on the median wall of the stipes and articulate with the posterior stipital sclerite along the distomedial stipital flange.The lacinial bar and lacinial comb are absent.The proximolateral galeal sclerite (pgs: Fig. 2A) is situated in the middle on the lateral wall of stipes and is connected proximally with the lacinial lever and distally with the basal galeal sclerite.The number of mechanosensory hairs in the proximolateral galeal setiferous patch (prs: Fig. 2A) is variable in different Sparasion species (Table 1) and overlaps the distolateral galeal sclerite (dgs: Fig. 2A, B,  D), which traverses the galeo-lacinial complex and is represented on both its medial and lateral walls (the complex is unilayered at the sclerite).The proximolateral and distolateral galeal sclerites are connected to each other by the lateral galeal crease.The apicomedial galeal plate is absent.The number of setae in the distolateral galeal setiferous patch (dgp: Fig. 2A) is variable in different Sparasion species (Table 1).The proximal galeal brush is absent.The single coeloconic sensillum of galea (cfs: Fig. 2B, D) is located distally on the median surface of the distolateral galeal sclerite.The single lacinial lobe (llb: Fig. 2A, B, D) extends anteroproximal whereas the galeal lobe (glb: Fig. 2A,  B, D) distal to the proximal galeal sclerites.The lacinial lobe and the proximal part of the galeal lobe are covered with short acanthae (ach: Fig. 2D), which comprise the spiculate patch of the lacinia and the spiculate patch of galea respectively.The galeal comb, galeal lamina and galeal fringe are absent.The velum (vlm: Fig. 2D) is fringed distally in some species (vlm: Fig. 2D).The stipital sclerite is absent from Sparasion.
The maxillary palp (1mp: Fig. 2B, D) is connected at the distal apex of the posterior stipital sclerite trough the ventral dististipital process (vdp: Fig. 2B) adjacent to the basal galeal sclerite.The maxillary palp is composed of five maxillary sclerites among  The number of setae in the proximal galeal brush 5-7 5-7 5-7 5-7 5-7 5-7 7-10 5-7 6 The number of setae in the distal galeal setiferous patch 18-19 18-20 18-20 11-14 18-20 17 27-34 18-20 22 The number of styloconic sensilla on the glossa 14-15 15-16 10-12 10-12 17 23 18-19 15-16 10 which the second sclerite of the maxillary palp is the shortest, and the fifth sclerite of the maxillary palp is always the longest (5mp: Figs 1A,C, 3D, E).The relative width of the maxillary palpal sclerites varies between Sparasion species and in some cases even between different sexes (Table 1).Two different setal types can be differentiated on the maxillary palp, based on their gross morphology.The type 1 seta (ss1: Fig. 3B) is a uniporous sensillum whereas the type 2 seta (ss2: Fig. 3B) is a longer mechanosensory hair.A type 1 seta is present on all but the first sclerite of the maxillary palp, which is glabrous in Sparasion sp. 4 and sp. 9 and bears only 1-2 type 2 setae in the rest of the species.Type 1 setae are evenly distributed on the third sclerite of the maxillary palp, on the fourth sclerite of the maxillary palp and on the fifth sclerite of the maxillary palp.Type 1 setae are located in 1-4 whorls of setae on the second sclerite of the maxillary palp.Type 2 setae occur only on the third, fourth sclerite of the maxillary palp and on the fifth sclerite of the maxillary palp.The number of type 2 setae is positively correlated with the width of the third sclerite of the maxillary palp and the fourth sclerite of the maxillary palp: type 2 setae are absent from the third sclerite of the maxillary palp if it is not increased in width relative to the second maxillary palpal sclerite.

Maxilla (skeletal muscles)
The cranio-cardinal muscle (cr-cd: Figs 1B, 4A, B) arises medially of the posterior site of origins of the tentorium and inserts on the cardo just laterally of the cranial fossa of the cardo (caf: Fig. 1B).The tentorio-cardinal muscle (tnt-cd: Fig. 1B) arises ventrally on the tentorium just laterally of the site of origin of the tentorio-stipital muscle (tnt-sti: Fig. 4A) and inserts laterally on the stipitocardinal hinge.The tentorio-stipital muscle arises ventrally from the tentorium, medially of the site of origin of the tentorio-cardinal muscle and inserts on the median margin of the posterior stipital sclerite just posterior of the lacinial lever.The cranio-lacinial muscle is absent.The stipito-lacinial muscle (stilac: Fig. 2A) arises from along the lateral margin of the posterior stipital sclerite and inserts apically on the lacinial lever.The single stipito-palpal muscle (sti-mp1: Figs 2A, 3A) and the stipito-galeal muscle (sti-gal: Fig. 3A) arise medially from the stipito-lacinial muscle, subsequently.The stipito-galeal muscle inserts on the basal galeal sclerite.The first intrinsic muscle of the maxillary palp, third intrinsic muscle of the maxillary palp and fourth intrinsic muscle of the maxillary palp are present, the second intrinsic muscle of the maxillary palp was not observed.No muscle was attached to the fifth maxillary sclerite.

Labium, distal hypopharynx (integument)
The postmentum is composed of a single interstipital sclerite that is elongate, rectangular, and is articulated with the posterior stipital sclerites proximolaterally at the proximomedial stipital flange (psm, pmf:  The prementum is connected to the stipes via a conjunctiva (stipito-premental conjunctiva) extending along the proximal margin of the premental arms (prm: Figs 1B, 3C, 4A, B, 5C, 6A-D) and the lateral margin of the prementum proximally of the arm.The  5C, D, 6A, D).The ventral premental face is flat, diamond-shaped and is equipped with campaniform sensillae of the prementum (cps: Fig. 2C) and distally-oriented mechanosensory hairs (msh: Fig. 2C).The number and pattern of both the campaniform sensilla and mechanosensory hairs and the length of the mechanosensory hairs are variable between different species and sexes (Table 1).The lateral face of the prementum is mostly overlapped ventrally by the distomedial stipital flange (Fig. 1A).The labial palpal excision (pin: Figs 2C, 3C) accommodating the base of the labial palp is distinct on the distolateral corner of the prementum.The labial palp is composed of three sclerites that are equipped with both the uniporous sensilla (type 1) and mechanosensory hairs (type 2).
The bilobed paraglossae arise proximolaterally of the basal glossal invagination and encircle the proximal part of the glossa.The elongate, triangular basiparaglossal sclerite (pls: Figs 3C, 5C, 6A-D, F) corresponds to a posterior lobe of the paraglossa whereas the larger anterior lobe of the paraglossa bears the distal, less sclerotised paraglossal acroglossal button (pgb: Fig. 6B).Proximally the paraglossa is continuous with the wall of the distal hypopharynx (dhy: Fig. 5A, C) and the paraglossal sclerite is connected to the distal hypopharyngeal sclerite via an elongate ligament.The basiparaglossal brush (bgb: Figs 4B, 6A, B, F) is distinct but the paraglossal sclerite and paraglossal annuli are absent.

Labium, distal hypopharynx (skeletal muscles)
The postmento-premental muscle is absent.The posterior tentorio-premental muscle (tntppmn: Fig. 4A, B) arises from the tentorium anterolaterally from the site of origin of the anterior tentorio-premental muscle (tnta-pmn: Fig. 4A, B) and inserts on the proximal part of the hypopharyngeal button.The anterior tentorio-premental muscle arises from the tentorium medially of the site of origin of the posterior tentorio-premental muscle and inserts proximomedially on the postmental-premental hinge.The premento-paraglossal muscle (pmn-pgs: Fig. 4A, B) arises medially from the internal edge corresponding to the premental ditch and from the intima of the median premental face anterior to the edge and inserts on the posterior glossal plate.The dorsal premento-salivarial muscle (pmnd-slv: Fig. 4A, B) arises distomedially from the premental arm and inserts dorsally on the salivarium.The ventral premento-salivary sclerite muscle (pmnv-slv: Figs 4A, B) arises from the proximal premental area and inserts proximomedially on the distal hypopharyngeal sclerite.The premento-palpal muscle arises anterolaterally from the site of origin of the premento-paraglossal muscle.The first intrinsic muscle of the labial palp and the second intrinsic muscle of the labial palp are present.The premento-glossal muscle is apparently absent.

The maxillo-labial complex of Sparasion
The term maxillo-labial complex (MLC) is used by Snodgrass (1935).However, many entomologists prefer to use the term labio-maxillary complex, e.g.Duncan (1939), Labandeira (1997), Jervis (1998), Vilhelmsen (1996), Krenn (2007).The reason for using the latter seems to be that it is more easily pronounced (Duncan 1939).In this paper the term maxillo-labial complex is preferred because it corresponds with the anatomical position of the component pieces.
The hymenopteran labium, unlike that of other holometabolan insects, is so tightly connected to the maxillae by the labiomaxillary hinge that they protract and retract together as a single unit (Duncan 1939, Snodgrass 1942, Vilhelmsen 1996, Krenn 2007).While the labiomaxillar hinge connects their proximal parts, the distal, more sclerotised regions of the maxillae and the labium still are able to move with some freedom in basal Hymenoptera (Vilhelmsen 1996, Beutel andVilhelmsen 2007) and in a few apocritan taxa (e.g. in Gasteruption, Evania (Evanioidea) (Fig. 8) and Gryon (Platygastroidea) Mikó, pers.obs.).However, in Sparasion and some other apocritan taxa (Ibalia (Cynipoidea) Ronquist & Nordlander, 1989, Vespula (Vespoidea) Duncan, 1939) where the posterior wall of the labium and maxilla are almost exclusively sclerotised, the freedom of the independent movement between the appendages is restricted: they can not be separated from each other and sometimes -e.g. in Sparasion -not even from the hypostoma.The development of rigid connections between sclerites that are flexibly connected in basal Hymenoptera seems to be an apocritan evolutionary trend, which is arguably related to their more sclerotised body (Vilhelmsen 2000a, 2000b, Vilhelmsen et al. 2010).
Although the MLC of Sparasion is reduced in size and highly sclerotized, we were able to homologize most of its anatomical structures to those of other Hymenoptera (Appendix 2, Figs 7 -9).We hypothesize that the platygastroid MLC is an anatomical system with enough phenotypic diversity to serve as a source of morphological characters for phylogenetic analyses and species diagnosis.

Maxilla
One consequence of the more heavily sclerotised and less moveable MLC is that the cardo remains relatively simple in Sparasion, retaining its main function: providing rigid attachment of the MLC to the cranium.The inner and outer processes of the cardo (Winston 1979) that articulate with the stipes are missing from Sparasion, similarly to other Proctotrupomorpha (e.g., Ibalia and Pelecinus pers.obs.).Because the stipito-cardinal articulation is absent, the cardo seemingly interacts with the posterior stipital sclerite only by the resilin rich stipito-cardinal hinge.Similarly to Sparasion, the cardo is not visible externally in these taxa and even if the MLC is in a protracted position, the cardo is obscured by the proximal portion of the principal carina of the stipes.
Different levels of sclerotization can be observed on the intercardinal and interstipital areas in different hymenopteran taxa.Only the intercardinal area contains a sclerite in basal Hymenoptera (Ross 1937), while both intercardinal or interstipital sclerites may be present in Apocrita.The intercardinal and interstipital areas are separated from each other by the labial suture (Snodgrass 1935, Prentice 1998).The median area of the MLC posterior to the suture contains an anterior and a posterior sclerite in some holometabolan insects (i.e.Coleoptera), the submentum and the mentum.This condition never occurs in Hymenoptera (see references listed in materials and methods section).Even in those Aculeata where two medial sclerites are in the postmental area, one is always anterior to the labial suture.Based on the their position relative to the stipites and cardines, the intercardinal postmentum of basal Hymenoptera might be homologous with the postmentum in other insects and the interstipital postmentum of Apocrita is most likely not homologous to these structures.The postmental area is fully membranous in many Apocrita (Evania, psm: Fig. 8; Vespula, Duncan 1939;Stenobracon, Alam 1951).Only the intercardinal sclerite is present in Ibalia (Ronquist and Nordlander 1989) leading Ritchie and Peters (1981) to homologize this structure with the mentum of other holometabolans.
Only the interstipital postmentum (Prentice 1998) is present in Sparasion.This sclerite is not connected with muscles, nor is it articulated with any other sclerites.It's only function might be to separate the posterior stipital sclerites from each other.The development of the principal carina arguably correlates with the presence of rigid connection between the stipes and neighboring sclerites.In those taxa, where the stipes articulates with the hypostoma, but not with the labium, the principal carina is present only laterally (Evania, pcs: Fig. 8).Both the medial and lateral portions of the carina are well developed in Sparasion, having two unique characteristics that were not found in other Hymenoptera (see references listed in the materials and methods section): 1.The median portion of the carina is divided into two sections that overlap each other and accommodate the proximal and distal part of the lateral premental margin.2. The presence of an "apical fringe", a branched flattened evagination along the distolateral margin of the carina.While the first specialization might be the consequence of the articulation between the posterior stipital sclerite and the prementum, the second is most probably related to the unique movement of the mandible in Sparasion.While pivotal axis of the mandible is anteroposterior in most Hymenoptera taxa (dorsoventral in a prognathous head) it is directed medi-olaterally in Sparasion and the mandibles are moved parallel to the body axis (Mikó et al. 2007).Due to this unique, oblique position of the mandible, the distolateral, fringed margin of the principal carina is positioned inside the internal concavity of the mandible and seemingly acts as a cleaning "brush".Similar movement of the mandible has been reported from many other Hymenoptera taxa, including two platygastrid genera, Tyrannoscelio and Encyrtocelio.It would be worthwhile to study the MLC of these taxa and to clarify whether the fringed lateral portion of the principal carina is unique for Sparasion or whether it can be found in other genera with modified mandible movement.
The presence of the campaniform sensillum of the stipes was considered as one of the synapomorphies of the clade composed of Platygastroidea and Cynipoidea (Sharkey et al. 2012).Although the sensillum is present in Sparasion and some other platygastrid taxa (Sharkey et al. 2012), it is absent from Triteleia, Calliscelio, Macroteleia, Apegus, Duta, Psilanteris, Anteris (Popovici and Fusu 2006), which implies that this character might be useful for generic classification in Platygastroidea.Prentice (1998) reported the presence of two apical sclerites on the galea, the apicolateral and apicomedial stipital plates.We were able to locate only one apical sclerite, the distolateral galeal sclerite on the galeo-lacinial complex of Sparasion.This sclerite traverses the complex and bears both the distolateral galeal setiferous patch and the medial coeloconic sensillum that define the apicolateral and apicomedial stipital plates respectively.
Appendage segments and annuli are ring-like and repetitive sclerites of the legs, antenna, labial palps and maxillary palps.While appendage segments have muscles attaching to them, annuli do not.Annuli are traditionally differentiated from appendage segments by names with the suffix "-mere" e.g.flagellomere and tarsomere.Among the five maxillary palpal sclerites of Sparasion the fifth one does not have muscle attachments.We observed a similar condition in Orthogonalys (Trigonalidae), where the fifth and sixth sclerites lack any muscle attachment (Fig. 9).If we apply the annuli vs. segment terminology system to these taxa, we should call the first four sclerites "palpal segments" and fifth sclerite in Sparasion and the fifth and sixth sclerites in Orthogonalys "palpomeres".To avoid misinterpretations of the segment identity of the palpi, and keeping a simple and easily applicable terminology we prefer to use palpal sclerites for the ring-like sclerites of the palpi.
Sparasion has five maxillary palpal sclerites that is the highest in Platygastroidea (Masner 1976).Since the presence of five maxillary palpal sclerites is a possible synapomorphy for Proctotrupomorpha (Sharkey et al. 2012), and is also shared by other, putatively basal lineages of Platygastroidea (i.e.Archaeoteleia, Nixonia and Plaumannion, Johnson et al. 2008) it is most probable that this condition is plesiomorphic for Platygastroidea.
The maxillary palp is located medially on the lateral margin of the posterior stipital sclerite in basal Hymenoptera distantly from the apical end of the sclerite bearing the base of the galea (Fig. 7B., Vilhelmsen 1996, Beutel andVilhelmsen 2007).In Sparasion the palp is connected to the apical vertex of the posterior stipital sclerite, adjacent to the base of the galeo-lacinial complex.This distal position makes it difficult to interpret the presence of minute anatomical structures such as the palpifer ("flexible and transparent, very difficult to detect structure" at the base of the maxillary palp, Prentice 1989).
The 2 nd , 3 rd and 4 th maxillary palpal sclerites are distinctly wider than the more proximal or distal maxillary palpal sclerites in some Sparasion species (Figures 3D, E).
The number and position of these modified sclerites are sexually dimorphic in some Sparasion species and are seemingly useful for species groups definitions.A widened 4th palpal sclerite was found in most species of the plesiomorphic platygastrid genus Nixonia, and representatives of Plaumannion, Archaeoteleia, Sceliomorpha and Neuroscelio (Johnson andMasner 2006, Johnson et al. 2008); the presence of enlarged 3 rd maxillary palpal sclerites have been reported from Sparasion (Johnson et al. 2008) and enlarged 2 nd and 3 rd sclerites from the putatively most primitive extant platygastroid genus, Huddlestonium (Masner et al. 2007).
Although the position of enlarged palpal sclerites in the maxillary palp has often been used for the classification of different Hymenoptera taxa (i.e.Evaniidae, Deans and Huben 2003;Aculeata, Bohart and Menke 1976), our knowledge about their possible function is rather incomplete.Albeit our study confirms Prentice's (1998) observation that enlarged sclerite size corresponds to larger muscle mass, the role of this modification in the mechanics of palpal movement is still unrevealed.
Although the presence of only two stipito-palpal muscles is considered as the Hymenoptera groundplan (stia-mp1, stip-mp1: Fig. 9; Beutel and Vilhelmsen 2007), similarly to Sparasion, only one maxillary plapal muscle has been reported from many Hymenoptera taxa (Snodgrass 1942, Matsuda 1957, Prentice 1998).The presence of resilin-rich conjunctiva at the base of the maxillary palpus in Sparasion supports Prentice's hypothesis that the expansion of the maxillary palpus is facilitated by a resilin rich region between the posterior stipital sclerite and the palpus in taxa with a single stipito-palpal muscle.
The terms, galea and lacinia refer usually to the evaginated distal, sclerotised regions of the maxillar cuticle that are adjacent to the sites of insertions for the stipito-lacinial, cranio-lacinal and the stipito-galeal muscles in insects.Although these muscles are present in most hymenopterans (sti-gal, sti-lac: Fig. 7A, and more proximal and more distal lobes can almost always be differentiated, the proximal limits of the galea and lacinia are difficult to define and thus these structures are difficult to homologize to that of other insects where the galea and lacinia are well sclerotised.Therefore we preferred to use galeal lobe and lacinial lobe instead of galea and lacinia in the present paper. Two distinct setiferous areas can be defined on the lateral area of the galeal lobe in Athalia: a proximal row of setae traversing the galea (prs: Fig. 7B) and a more distal setiferous patch (dsp: Fig. 7B).The presence of these two setiferous areas seems to be consistent within Hymenoptera (Prentice 1998) and can be used for the delimitation of areas of the galeo-lacinial complex.
In Sparasion, similarly to some other, more derived Hymenoptera taxa these setiferous areas correspond to two sclerites, the proximolateral and distolateral sclerites of the galea (Prentice 1998, Ronquist andNordlander 1989).Two distal sclerites are located on the medial wall of the galeo-lacinial complex in Athalia (pgs, dgs: Fig. 7A), with some campaniform sensillae (cfs: Fig. 7A).Based on the presence of the sensilla on the medial wall of the distal galeal sclerite of Sparasion it is possible that the distal galeal sclerite, or at least its medial part (the sclerite traverses the galeo-lacinial complex) is homologous with one of the apical galeal sclerites of Athalia.
Although the velum is well developed in numerous other Hymenoptera (Prentice 1998), we are not aware of any case in the order where the lobe is fringed apically as it was found in some Sparasion species (vlm: Fig. 2D).
The galeal comb and the galeal lamina are important characters that have been used in aculeate systematics (Prentice 1998, "comb of galea" in Michener 1944, "Borstenkamm" in Ulrich 1924).Although neither of these structures are present in Sparasion, they are present in some other scelionines (Encyrtoscelio, Teleas, Trimorus Popovici pers.obs.).

Labium
The prementum is articulated with the stipes via the premento-stipital articulation that is composed of the premental ditch, premental carinae, and the principal carina of the stipes.Duncan (1939) reported a similar connection between the stipes and the prementum and considered its importance in the simultaneous movement of these two structures.Although we are unaware of other hymenopterans with a complete premento-stipital articulation, the premental carinae are present in some Evaniidae (pmc: Fig. 8) and in some platygastroid genera (illustrations in Popovici and Fusu 2006).Vilhelmsen (1996) proposed the presence of acanthae on the hypopharyngeal rod as a possible synapomorphy for Apocrita.In Sparasion and in some other apocritans (e.g.Vespula, Duncan 1939; in Apoidea, =spiculate patch of the hypopharynx in Prentice 1989, Evania pers.obs.) two regions of the hypopharyngeal rod, the hypopharyngeal pecten (hpc: Fig. 10) and the basiparaglossal brush (bgb: Fig. 10) are extensively covered with acanthae.Contraction of the posterior tentorio-premental muscle might protract, whereas contraction of the ventral premento-salivarial muscle retract the hypopharyngeal buttons.The distal hypopharyngeal invagination, which is apparently unique for Platygastroidea, is defined by the hypopharyngeal button.Protraction and retraction of the button, therefore, might actually control the orientation of the invagination.We were not able to locate an infrabuccal pouch (Fig. 10) in Sparasion between the transverse line connecting the tips of the lateral arms of the prementum and the sitophore in basal Hymenoptera (Vilhelmsen 1996).
The maximum number of labial palpal sclerites in Apocrita is four (some Formicidae (Gotwald, 1969), Braconidae (Belokobylskij, 2006), Vespinae (Duncan, 1939)).In Sparasion, the labial palp is composed of three sclerites that are moved directly by muscles.In those Hymenoptera where the labial palp is composed of four sclerites (Vilhelmsen and Beutel 2007, Gotwald 1969, Belokobylskij and Chen 2006, Duncan 1939) the apical sclerite has no muscles and is considered to be a secondary subdivision of the apical segment.The presence of four labial palp sclerites is considered a hymenopteran synapomorphy (Vilhelmsen and Beutel 2007) and the ground plan of almost all other apocritan superfamilies (Sharkey et al. 2012).The ground plan of a three-segmented labial palp of Platygastroidea is probably the result of the secondary loss of the apical palpal sclerite.Duncan (1939) hypothesized that the glossal annuli have rasping function or are involved in retaining liquids in Vespinae.Glossal annuli with elongated and well developed spatulate annular hairs are present in most Apocrita (Duncan 1939, Prentice 1998, Ronquist and Nordlander 1989, Dangerfield et al. 2001, Popovici and Fusu 2006) while are present only in a few basal Hymenoptera taxa (Cephoidea, Megalodontoidea and Orussioidea, Vilhelmsen 1996).
Along the proximal margin of distal edge of glossa in Sparasion, a row of 9-23 apical glossal setae can be observed.These setae are styloconic sensilla, which are considered to be bimodal contact chemo-mechanosensillae (Shields 2010).Although they have never been mentioned elsewhere, these styloconic setae are present in other Hymenoptera (Evania, sts: Figs 8, 10, Gasteruption, Ibalia, Mikó pers.obs.) and might play crucial role in the chemo-and mechanosensation in Apocrita.The ventral glossal lines have been reported only from a few Hymenoptera (Salman 1929, Prentice 1998, Evania, Fig. 8).The lines radiate from the posterior glossal plate and extend toward the apical glossal hairs and therefore might be related to the presence of these styloconic sensilla.We have found the lines present in taxa whith apical styloconic sensilla.

Appendix 1
Specimens examined.The sclerite that is ringlike and is connected distally to the third sclerite of the maxillary palp via conjunctiva.
http://purl.obolibrary.org/obo/HAO_0002113 galeal comb The row of setae that is located on the medial wall of the galeo-lacinial complex proximal to the coeloconic sensilla of galea.
http://purl.obolibrary.org/obo/HAO_0002133 galeal lamina The lobe that is located medially on the internal wall of the galeo-lacinial complex and margined by the galeal comb.The ligament that connects the proximolateral margin of the prementum with the proximal part of the ligula.
http://purl.obolibrary.org/obo/HAO_0000408 hys hypostoma The area that extends on the posterior (ventral) margin of the oral foramen along the site of attachments of the conjunctiva connecting the cranium with the maxillae and is delimited laterally by the pleurostomal fossa.The articular process that bears the cardinal condyle of the cranium.http://purl.obolibrary.org/obo/HAO_0002073 maxillo-labial complex The anatomical cluster that is composed of the maxillae and the labium and is connected by conjunctivae laterally to the cranium along the hypostoma, to the mandible along the proximomedial margin of the mandible and proximally to the hypopharynx.The tentorio-labial muscle that arises from the cranium and inserts distally on the labium adjacent to the level of the salivary orifice.
http://purl.obolibrary.org/obo/HAO_0000264 postmental area The area that is limited distally by the posterior margin of the prementum and laterally by the median margins of the cardines and the stipites.
http://purl.obolibrary.org/obo/HAO_0002226 postmentopremental muscle The labial muscle that is unpaired, arises from the postmentum and inserts on the proximal margin of the prementum.http://purl.obolibrary.org/obo/HAO_0000803 psm postmentum The anatomical cluster that is composed of the sclerites that are on the postmental area.
http://purl.obolibrary.org/obo/HAO_0000785 prm premental arms The area of the lateral premental face that receives the site of origin of the dorsal premento-salivarial muscle.
http://purl.obolibrary.org/obo/HAO_0002155 pmc premental carina The flange that is adjacent with the border between the ventral and lateral premental faces and that overlaps externally the median part of the posterior stipital sclerite.

premento-glossal muscle
The labial muscle that arises on the ventral part of the prementum, laterally to the ventral premento-salivarial muscle and inserts on the anterior glossal plate. http://purl.obolibrary.org/obo/HAO_0000377

premento-palpal muscle
The labial muscle that arises from the prementum and inserts on the first sclerite of the labial palp.
http://purl.obolibrary.org/obo/HAO_0000314 pmn-pgs prementoparaglossal muscle The labial muscle that arises from the ventral part of the prementum, anterior to the origin of the premento-glossal muscle and ventral premento-salivarial muscle and inserts just distally of the distal margin of the prementum.
http://purl.obolibrary.org/obo/HAO_0000687 pmn prementum The sclerite that is median, is connected via conjunctiva along its proximolateral margins to the stipites, is articulated with the labial palps, is continuous along its distal margin with the ligula and distolateral margins with the distal hypopharynx and receives the site of attachments of the extrinsic labial palp muscles.
http://purl.obolibrary.org/obo/HAO_0000804 pcs principal carina of the stipes The flange that extends along the margin of the posterior stipital wall.
http://purl.obolibrary.org/obo/HAO_0002129 pmf proximomedial stipital flange The medial part of the principal carina of the stipes that is overlapped distally by the distomedial stipital carina and overlaps the lateral premental face and the proximal part of the prementum.
http://purl.obolibrary.org/obo/HAO_0002218 svr salivarium The area that is at the proximal end of the salivary duct and corresponds to the site of insertion of the dorsal and ventral prementosalivarial muscles.

Figure 1 .
Figure 1.Mouthparts of Sparasion sp.A SEM micrograph showing the mouthparts, posterior (external) view, distal to the bottom B CLSM volume rendered image showing the maxillo-labial complex, anterior (internal) view, distal to the bottom (doi: 10.6084/m9.figshare.861065,doi: 10.6084/m9.figshare.861058)C Line drawing showing the maxillo-labial complex, posterior (external), distal to the bottom D Bright field image showing the cardo of Sparasion, lateral to the left.

Figure 3 .
Figure 3. Maxilla and labium of Sparasion.A SEM micrograph showing the skeletomuscular system of the maxilla, posterior (internal) view, distal to the top B SEM micrograph showing the maxillary palp, distal to the top C Bright field image showing the labium, lateral view, distal to the left D, E Bright field image showing the maxillary palps, distal to the left.

Figure 4 .
Figure 4. CLSM volume rendered images showing the skeletomuscular system of the labium of Sparasion, medial view, distal to the left.

Figure 5 .
Figure 5. Labium and distal hypopharynx of Sparasion.A SEM micrograph showing the labium and distal hypopharynx, anterolateral view, distal to the left B SEM micrograph showing the glossal annuli, anterior view, distal to the left C, D CLSM volume rendered images showing the labium with retracted glossa and paraglossae, distal to the left C lateral view (doi: 10.6084/m9.figshare.861064)D medial view (doi: 10.6084/m9.figshare.861061).