Arthropod Structure & Development 50 (2019) 1e14

Contents lists available at ScienceDirect

Arthropod Structure & Development

journal homepage: www.elsevier.com/locate/asd

Small, but oh my! Head morphology of adult Aleuropteryx spp. and effects of miniaturization (Insecta: Neuroptera: Coniopterygidae)

* Susanne Randolf , Dominique Zimmermann

Natural History Museum Vienna, 2nd Zoological Department, Burgring 7, 1010, Vienna, Austria article info abstract

Article history: We present the first morphological study of the internal head structures of adults of the coniopterygid Received 15 October 2018 genus Aleuropteryx, which belong to the smallest known lacewings. The head is ventrally closed with a Accepted 1 February 2019 gula, which is unique in adult Neuroptera and otherwise developed in Megaloptera, the sister group of Neuroptera. The dorsal tentorial arms are directed posteriorly and fused, forming an arch that fulfills functions otherwise taken by the tentorial bridge. A newly found maxillary gland is present in both sexes. Keywords: Several structural modifications correlated with miniaturization are recognized: a relative increase in Miniaturization the size of the brain, a reduction in the number of ommatidia and diameter of the facets, a countersunken Brain fi Musculature cone-shaped ocular ridge, and a simpli cation of the tracheal system. The structure of the head differs Maxillary gland strikingly from that of the previously studied species Coniopteryx pygmaea, indicating a greater vari- Tentorium ability in the family Coniopterygidae, which might be another effect of miniaturization. Gula © 2019 Elsevier Ltd. All rights reserved.

1. Introduction With nearly 560 described species, Coniopterygidae are one of the four most speciose neuropteran families, inhabiting all Miniaturization is a common phenomenon in many groups of zoogeographical regions with the exception of extremely cold animals and has major effects not only on the morphology but also areas (Sziraki, 2011). Three subfamilies are recognized: Conio- on the physiology, ecology and life history of the miniaturized or- pteryginae, Aleuropteryginae, and the highly unusual neotropical ganism (Hanken and Wake, 1993). Very small organisms are not Brucheiserinae with only four known species (Sziraki, 2011). simply reduced in size; they must develop solutions to cope with Several authors even proposed to elevate the subfamilies to family size-related constraints (Schmidt-Nielsen, 1984). This leads to a rank (Tillyard, 1926; Carpentier and Lestage, 1928; Riek, 1975), range of considerable reorganizations of structures, affecting because the differences between them are substantial: They differ almost all organs and tissues that are forced to fit within tiny vol- in the venation of fore- and hindwings, in Coniopteryginae the umes (Polilov, 2015a, b; 2016c). last abdominal spiracles are reduced, and in Aleuropteryginae the Neuroptera are highly variable with respect to their body size, galea is divided and plicatures are present on the abdomen. having forewing lengths from 2 mm to over 70 mm (New, 1989). Coniopterygidae are free-living and have a lifespan of several Singular species with a small body size are present in different weeks (Muma, 1967; Henry, 1976). Niven and Farris (2012) sug- neuropteran families. The Coniopterygidae, or “dustywings”, gested that miniaturized species have severe behavioral deficits. however, are the only family with a small body size throughout all This does not seem to be the case for Coniopterygidae, which species, and can thus be regarded as the midgets of Neuroptera perform a variety of more or less complex behaviors, similar to their (New, 1989). Their body and wings are usually covered with the larger relatives: Being mainly carnivorous, they detect and over- eponymous whitish or brownish dust of waxy particles (Enderlein, power their prey, including soft-bodied arthropods in Conio- 1906) secreted by hypodermal wax glands (Withycombe, 1925). pteryginae and scale insects in Aleuropteryx (Gepp, 1967; Henry, 1976). Their mating is preceded by a rather intricate precopula- tory behavior of both sexes (Johnson and Morrison, 1979), and when disturbed, they can be observed to “play possum” or escape in a fluttery flight followed by landing on the underside of vege- * Corresponding author. tation (Johnson, 1980). E-mail addresses: [email protected] (S. Randolf), dominique. [email protected] (D. Zimmermann). https://doi.org/10.1016/j.asd.2019.02.001 1467-8039/© 2019 Elsevier Ltd. All rights reserved. 2 S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14

Data on the head morphology of Coniopterygidae are sparse: 2.4. Micro-computered tomography Only recently, the head anatomy of Coniopteryx pygmaea, a species representing the subfamily Coniopteryginae, was investigated and One specimen of Aleuropteryx was dehydrated and stained for described in detail (Randolf et al., 2017). Otherwise, only few data 24 h with a 1% (w/v) solution of elemental iodine (I2) in absolute are available on the general external morphology of the head ethanol. After staining, the sample was rinsed for several hours in (Shepard, 1967; Meinander, 1972), and one scanning electron absolute ethanol and mounted in a plastic pipette tip again in ab- microscopic study comparing the surface structures and sensilla of solute ethanol. It was scanned using an XRadia MicroXCT-400 (Carl Aleuropteryx and Semidalis as representatives of the two sub- Zeiss X-ray Microscopy, Pleasanton, CA, USA) at 40 kVp/50 mA using families Aleuropteryginae and Coniopteryginae (Zimmermann the 20X detector assembly. Projections were recorded with 120s et al., 2009). In the present study, we describe the head exposure time (camera binning 2) and an angular increment of 0.2 morphology of Aleuropteryx juniperi and Aleuropteryx loewii. With a between projections. Tomographic slices were reconstructed with a body length of only 2 mm in both sexes, Aleuropteryx Low,1885€ (Fig. voxel resolution of 0.95 mm using the software provided with the 1) is one of the smallest Coniopterygidae and the eponymous genus microCT system. The reconstructed volume image was exported as for the subfamily Aleuropteryginae. We aim to a) recognize effects DICOM sequence. of miniaturization by comparing it to the head morphology of larger neuropteran representatives, and b) assess the degree of 2.5. 3D-reconstruction intrafamiliar variability by comparing it with the similarly sized species C. pygmaea (Randolf et al., 2017). Reconstructions were made using the software Amira 6.3.0. We computed new volume datasets from the original data and the la- bels data object by using the arithmetic function in Amira 6.3.0 2. Material and methods (Kleinteich et al., 2008). Volumes were calculated from the labels with the Material statistics function in Amira 6.3.0. Isosurfaces of 2.1. Taxa examined the segmented volumes were created and extracted. Since the resolution of the microCT images was insufficient for reconstruc- Male specimens of A. juniperi Ohm (1968), were examined by tion of detailed anatomy, histological sections were photographed microCT scans and histological cross sections, one specimen of with a Nikon DS-Fi1 camera (2/3 inch sensor), mounted on a Nikon A. loewii Klapalek (1894), was examined by histological longitudinal Eclipse 80i microscope with a 0,7x C-Mount Adapter in the trin- sections. Additionally cross and longitudinal sections of female ocular tube. The resolution was 2560 1920 pixel. To be able to Aleuropteryx sp. were studied. Specimens were collected in front of open a larger amount of images in Amira, the images were con- the Museum of Natural History Vienna, Maria-Theresien-Platz in verted to greyscale. Every single section was imaged, imported and 2018 at Thuja sp., the specimen for the microCT was collected in aligned in Amira 6.3.0. Scheibbs, Lower Austria in 1995 at Juniperus communis. For Based on these reconstructions, the schematic drawing in Fig. 5 comparative purposes, microCT scans and histological sections of were made with Adobe Illustrator CC 2018. MicroCT image stacks the following specimens were studied: Chrysoperla carnea (Ste- are deposited in the Natural History Museum Vienna and the phens, 1836) (Chrysopidae), Chrysopa dorsalis Burmeister, 1839 University of Veterinary Medicine Vienna. Histological sections are (Chrysopidae), Podallea vasseana (Navas, 1910) (Berothidae), housed in the Natural History Museum Vienna, 2nd Zoological Mucroberotha vesicaria Tjeder, 1968 (Rhachiberothidae), Poly- Department. stoechotes punctata (Fabricius, 1793) (Ithonidae sensu Winterton and Makarkin, 2010), Micromus variegatus (Fabricius, 1793) (Hem- 2.6. Terminology erobiidae), Myrmeleon hyalinus distinguendus Rambur, 1842 (Myrmeleontidae). The classification of cephalic musculature follows Wipfler et al. (2011), of musculature of the circulatory system Wipfler and Pass (2014) and Friedrich and Beutel (2008) for thoracic musculature 2.2. Semithin-sections (Ivlm1, Fig. 6A; Ivlm3, Fig. 6A and B). In addition, the classification by von Keler (1963) is provided in brackets in the results section. Specimens were put to death with 96% alcohol and embedded in The terminology of the external head capsule follows Shepard Hard-Plus Resin. Semithin histological sections, 1 mm thick, were (1967) and the terminology of the mouthparts follows Meinander made with a diamond knife on a Leica EM UC7 (Ludwig Boltzmann (1972). Institute for Experimental and Clinical Traumatology) and stained with 0.1% toluidine blue; sections are deposited at the Natural 3. Results History Museum Vienna. 3.1. Head capsule

2.3. Scanning electron microscopy The orthognathous head of Aleuropteryx sp. (Fig. 1) is elongate and consistently dark brown in both sexes. Occipital, frontal and Specimens were dehydrated in an ethanol series and 100% subgenal sulci are not discernible so the head regions frons, vertex, acetone and chemically dried using HMDS (hexamethyldisila- genae and postgenae can only be defined by their position. The zane; after Brown, 1993). Subsequently, they were mounted on anterior part of frontogenal sulcus, delimiting the frons from the tabs and sputter coated with gold. Scanning electron micro- genae is externally not discernible but internally represented by graphs were taken with a JEOL JSM-6610 (Natural History frontogenal ridges. Museum Vienna) and a Philips XL20 scanning electron micro- The temporal sulcus runs between the dorsolateral angle of the scope (University of Vienna, Department of Core Facility Cell occipital foramen and the mesal rim of the compound eye. It is Imaging and Ultrastructure Research). SEM images were used to externally visible as almost black line and internally represented by determine the number of ommatidia per eye and the diameter of a prominent temporal ridge (Fig. 6F: tr), delimiting the roundish the facets. vertex of the genae. The postoccipital sulcus (Fig. 6A: poccps), to S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14 3

3.3. Labrum

The labrum (Figs. 2A,B; 6A-C: lbr) is of amber color and trans- versely oval. Its proximal margin is medially covered by the ante- clypeus. Labrum and anteclypeus are connected by a membrane. The tormae are well-developed and slightly converging. Musculature. 0lb1: M. frontolabralis (M8), absent; 0lb2:M. frontoepipharyngalis (M9), O: frons, I: on the tormae; 0lb3:M. epistoepipharyngalis (M10), absent; 0lb4: M. labralis transversalis, absent; 0lb5: M. labroepipharyngalis (M7), absent; 0lb6: M. lab- rolabralis, absent.

3.4. Antenna

fl Fig. 1. Aleuropteryx sp., habitus. Scale bar: 1 mm. Photo: K. S. Matz. Scapus, pedicellus and the agellomeres are of the same shade of brown in both sexes. The scapus is about twice as long as broad (Figs. 2A; 3A; 6B: sc). It articulates with the lateral antennifer of the which the cervical membrane attaches, is dorsomedially broad- antennal foramen. The pedicellus (Figs. 2A; 6B: ped) articulates ened. The postocciput itself is deeply inflected and covered by the with a mesal condyle of the scapus. The pedicellus is about two- cervical membrane. Postoccipital sulcus and temporal sulcus blend thirds the length of the scapus and there is a ventral spine in into each other. The occipital condyles are triangular (Fig. 2E: occc). males at its distal end (Fig. 6B: sp). Both flagella in females consist The occipital foramen (Fig. 2E: occf) is ventrally confined by a gula of 21 flagellomeres whereas in the two examined males one fla- sensu Snodgrass (1935) (Figs. 2E,F; 6AeC; 7A: gu). The gular sutures gellum consists of 16, the other of 17 flagellomeres; in both sexes are externally visible as dark lines and represented internally as the proximal flagellomeres are shorter than the distal ones and the two lateral gular ridges (Fig. 2E: gus) each ending in the posterior terminal flagellomere is enlarged. The flagellomeres of both sexes tentorial pits. The compound eyes are oval (Figs. 2A; 6E,F: cpe), only are distinctly longer than broad. slightly protruding and bear short inter-ommatidial setae (sensu Musculature (Figs. 3A; 6B,E). 0an1: M. tentorioscapalis anterior Kristensen and Nielsen, 1979), mainly on their dorsal side. The (M1), O: laminatentorium and anterior tentorial arm, I: ventral ocular sulcus is blackish and its internal projection, the ocular ridge margin of scapus; 0an2: M. tentorioscapalis posterior (M2), O: (sensu Snodgrass, 1935, Figs. 3B; 6F: or), is cone-shaped and dorsal tentorial arm, I: dorsal margin of scapus; 0an3: M. tentor- countersunk into the head capsule. The compound eyes are ioscapalis lateralis (M3), O: dorsal tentorial arm, I: lateral margin of composed of 182 ommatidia each (n ¼ 2) and the diameter of the scapus; 0an4: M. tentorioscapalis medialis (M4), O: dorsal tentorial facets is 11,6 ± 0,7 mm(n¼ 32). Ocelli are absent. arm, I: medially on the base of scapus; 0an5: M. frontopedicellaris, The antennal foramina are oval; the antennal sockets are absent; 0an6: M. scapopedicellaris lateralis (M5), O: lateral wall of shallow and reach the ocular sulcus laterally. A distinct antennifer is scapus, I: lateral base of pedicellus; 0an7: M. scapopedicellaris present at the anteriolateral margin of the antennal foramen. A medialis (M6), O: mesal base of scapus, I: mesal base of pedicellus, frontoclypeal sulcus, transversely connecting the anterior tentorial in front of condylus of scapus; 0an8: M. intraflagellaris, absent; pits (Fig. 2A: atp) is neither externally discernible nor forming an 0an9: M. scapopedicellaris posterior, O: posteromesal lower wall of internal ridge. The clypeus is divided into an anterior anteclypeus scapus, I: posterior base of pedicellus; 0an10: M. scapopedicellaris (Figs. 2A; 6B: acly) and a posterior postclypeus (Figs. 2A; 6B: pcly). anterior, O: anterior basal margin of scapus, I: anterior basal margin The anteclypeus is heavily sclerotized, medially crescent-shaped in of pedicellus. cross section, externally visible as depression and without muscle attachment. The postclypeal area is posteriorly fused with the 3.5. Mandible frons. The mandibles (Figs. 2AeC; 3B; 6A,B,E: md) are of the same 3.2. Tentorium amber color as the labrum. Both mandibles have an apical (Fig. 6E: ai) and a subapical incisivus (Fig. 6E: sai). The molar process of the The anterior tentorial pits (Figs. 2A; 7A: atp) are roundish, the right mandible is broader than the molar process of the left anterior tentorial arms (Figs. 3A,D; 6E; 7A: ata) are slender, curved mandible. The primary mandibular joint is built up by a globular inward and posteriorly broadened to laminatentoria. Just upon protrusion of the mandible that articulates with a shallow emar- those, the anterior tentorial arms give birth to the dorsal tentorial gination of the head capsule. The secondary mandibular joint arms (Figs. 3A,D; 4B; 6A,B; 7A: dta). The dorsal tentorial arms are (Fig. 6E: smj) is formed by a cavity in the mandible and a corre- directed posteriorly and fused, forming an arch. Anterior and dorsal sponding protrusion of the head capsule. tentorial arms are hollow throughout. Musculature (Figs. 3B; 6B,D,E,F). 0md1: M. craniomandibularis The tentorial bridge (Figs. 3D; 4A,B; 6A: tb) is massiv and curved internus (M11), numerous bundles with different origins, O: one outward, it bears a massiv median process projecting ante- bundle on the postoccipital sulcus, vertex and gena (a), one on the roventrally (Fig. 3D: mep). It is fused with the gula, forming a chasm vertex between the antennal foramina (b) and several bundles from between the posterior tentorial pits (Figs. 2F: arrow; 7A: ptp). The the frons and genae laterally to the tentorial pits and from the posterior tentorial arms are hardly discernible as separate struc- ocular ridge (c), I: with a strongly developed tendon at mesal basal tures; they are fused with the tentorial bridge (Figs. 3D; 4A,B; 6A: margin of mandible; 0md2: M. craniomandibularis externus tb) and only recognizable by their hollowness. The posterior ten- anterior, absent; 0md3: M. craniomandibularis externus posterior torial pits are located laterally in the gular-tentorial chasm (Fig. 2F, (M12), O: genae below the compound eyes and ocular ridge pos- arrow). terior to 0md1; 0md4: M. hypopharyngomandibularis (M13), ab- Musculature. The muscles of the tentorium 0te1e0te6 are sent; 0md5: M. tentoriomandibularis lateralis superior, absent; absent. 0md6: M. tentoriomandibularis lateralis inferior (M14), absent; 4 S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14

Fig. 2. Aleuropteryx, head, SEM images. AeD, Aleuropteryx sp., female, EeF Aleuropteryx juniperi, male. A frontal view, B detail of A, C galea, detail of B, D vertex: wax gland, E posterior view, F detail of E, arrow: position of posterior tentorial pit. Abbreviations: acly e anteclypeus, atp e anterior tentorial pit, ca e cardo, cpe e compound eye, dga e distigalea, fr e frons, ga e galea, gu e gula, gus e gular sulcus, lac e lacinia, lbp e labial palp, lbr e labrum, lig e ligula, md e mandible, mt e mentum, mtr e mental ridge, mxp e maxillary palp, occc e occipital condyle, occf e occipital foramen, pcly e postclypeus, ped e pedicellus, pg e palpiger, prga e process of the galea, sc e scapus, smt e submentum, st e stipes. Scale bars: A,E 100 mm, B,F 50 mm, C 10 mm, D 2 mm. S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14 5

Fig. 3. A. juniperi, male, schematic drawings. A antennal muscles, B mandibular muscles, C intrinsic maxillary muscles, D labial muscles. Abbreviations: ata e anterior tentorial arm, ca e cardo, dta e dorsal tentorial arm, ga e galea, lac e lacinia, lbpm1, 2, 3 e labial palpomere 1, 2, 3, lig e ligula, lt e laminatentorium, md e mandible, mep e median process, mt e mentum, mtr e internal mental ridge, mxpm1 e maxillary palpomere 1, or e ocular ridge, sc e scapus, scp e semicircular process, smt e submentum, st e stipes, tb e tentorial bridge, 0an1 e M. tentorioscapalis anterior, 0an2 e M. tentorioscapalis posterior, 0an3 e M. tentorioscapalis lateralis, 0an4 e M. tentorioscapalis medialis, 0la5 e M. tentoriopraementalis, 0la8 e M. submentopraementalis, 0la10 e M. submentomentalis, 0la14 e M. praementopalpalis externus, 0la16 e M. palpopalpalis labii primus, 0la17 e M. palpopalpalis labii secundus, 0md1a,b,c e M. craniomandibularis internus with origin on postoccipital sulcus, vertex and gena (a), on vertex between antennal foramina (b) on frons, gena and ocular ridge (c), 0md3 e M. craniomandibularis externus posterior with origin on gena (ge), ocular ridge (or), 0mx6 e M. stipitolacinialis, 0mx7 e M. stipitogalealis, 0mx8 e M. stipitopalpalis externus, 0mx9 e M. stipitopalpalis medialis, 0mx10 e M. stipitopalpalis internus; Arrows indicate the orientation of the head: A-P e anteroposterior axis, L-R e left-right axis. Scale bars: A, B, D: 50 mm, C: 100 mm.

0md7: M. tentoriomandibularis medialis superior, absent; 0md8: The lacinia (Figs. 2B; 3C: lac) is heavily sclerotized at its base at M. tentoriomandibularis medialis inferior, absent. the insertion sites of its adductor muscles. The maxillary palp (Fig. 2A: mxp) is five-segmented, the first (Fig. 3C: mxp1) and the fifth palpomere are longer than the palpomeres two, three and four. 3.6. Maxilla A palpifer is not developed. Musculature (Figs. 3C; 6AeF). 0mx1: M. craniocardinalis (M15), The maxillae and the labium are connected by membrane. The absent; 0mx2: M. craniolacinialis (M19), two bundles, O: gena next cardo is triangular (Figs. 2E,F; 3C; 6A,D: ca) and articulates with the to the origin of 0md3, I: basal edge of lacinia; 0mx3: tentorial bridge medially to the posterior tentorial pits by a semi- M. tentoriocardinalis (M17), O: along posterior half of anterior circular process (Fig. 3C: scp). It is reinforced by an internal cardinal tentorial arms until tentorial bridge, I: cardo; 0mx4a, b: M. ten- ridge (Fig. 6D: car). The stipes (Figs. 2E,F; 3C; 6A,D,F: st) is not toriostipitalis anterior (M18), bipartite, O: anterior tentorial arms divided into a basi- and mediostipes, narrows anteriorly and the just anterior to the origin of 0mx3 (a) and median process of ten- proximal half of its inner margin is reinforced by an internal stipital torial bridge (b), I: stipital ridge; 0mx5: M. tentoriostipitalis pos- ridge. The convex galea (Figs. 2B; 3C: ga) is composed of a basigalea terior, absent; 0mx6: M. stipitolacinialis (M20), O: basally and (subgalea sensu Snodgrass, 1935; Ferris, 1940, Beutel et al., 2010) laterally until mid-length of stipes, I: basal margin of lacinia with a (Fig. 6D: bga), a distigalea (Figs. 2C; 6D: dga) and a finger-like long tendon; 0mx7: M. stipitogalealis (M21), O: medially on the process of the galea (Fig. 2C: prga). stipes and on the stipital ridge, I: basal margin of distigalea; 0mx8: 6 S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14

Fig. 4. A. juniperi, male, schematic drawings. A hypopharynx and salivary system, lateral view, B prepharyngeal tube and pharynx, lateral view. Abbreviations: dta e dorsal tentorial arm, fg e frontal ganglion, hyph e hypopharynx, hyssc e hypopharyngeal suspensorial sclerite, lig e ligula, mt e mentum, mtr e internal mental ridge, oa e oral arm, pg e palpiger, ph e pharynx, ppht e prepharyngeal tube, sd e salivary duct, slv e salivarium, smt e submentum, tb e tentorial bridge, 0bu1 e M. clypeobuccalis, 0bu2 e M. frontobuccalis anterior, 0bu5 e M. tentoriobuccalis anterior, 0bu6 e M. tentoriobuccalis posterior, 0ci1 e M. clypeopalatalis. 0hy1 e M. frontooralis, 0hy3 e M. craniohypopharyngalis, 0hy7 e M. praementosalivaris anterior, 0hy8 e M. praementosalivaris posterior, 0hy12 e M. hypopharyngosalivaris. A-P e anteroposterior axis, L-R e left-right axis. Scale bars: 100 mm.

M. stipitopalpalis externus (M22), O: broad muscle, stipital ridge, I: O: lateral and mesal margin of palpomere 3, I: mesal margin of distal margin of basal palpomere; 0mx9: M. stipitopalpalis medi- palpomere 4; 0mx15: M. palpopalpalis maxillae quartus (M27), O: alis, O: stipes laterally to 0mx8, I: ventral edge of palpomere 1; lateral and mesal wall of palpomere 4, I: mesal margin of palpo- 0mx10: M. stipitopalpalis internus (M23), O: stipes and stipital mere 5. ridge anteriad 0mx8, I: median margin of palpomere 1; 0mx11:M. stipitalis transversalis, absent; 0mx12: M. palpopalpalis maxillae 3.7. Labium primus (M24), O: lateral and mesal margin of palpomere 1, I: mesal margin of palpomere 2; 0mx13: M. palpopalpalis maxillae secun- Submentum (Figs. 2F; 3D; 4A; 6B,C: smt) and mentum (Figs. 2F; dus (M25), absent; 0mx14: M. palpopalpalis maxillae tertius (M26), 3D; 4A; 6C: mt) are strongly curved and connected by a membrane. The posterior submental margin is fused with the tentorial bridge and its posterior boundary not exactly determinable. The mentum is narrow and lateral internal mental ridges (Figs. 2F; 3D; 4A: mtr) project anteriorly and are in close contact with the hypopharyngeal suspensorial sclerites. The prementum consists of two cylindrical palpigera (sensu Meinander, 1972), ventrally fused to the half of their length (Figs. 2F; 4A; 6C: pg) and a trapezoidal ligula (sensu Matsuda, 1965: fused glossae) (Figs. 2E; 3D; 4A; 6B,C,F: lig). Para- glossae sensu Matsuda (1965) are absent. The labial palps (Fig. 2A,E: lbp) consist of three palpomeres (Fig. 3D: lbpm1, 2, 3), with the second being the shortest. The third labial palpomere is bulbously widened. Musculature (Figs. 3D; 6B). 0la1: M. postoccipitoglossalis medialis, absent; 0la2: M. postoccipitoglossalis lateralis, absent; 0la3: M. postoccipitoparaglossalis, absent; 0la4:M.post- occipitopraementalis, absent; 0la5: M. tentoriopraementalis (M29), two bundles, O: on the median process of the tentorial bridge, I: posterior margin of prementum; 0la6: M. tentoriopar- aglossalis (M30): absent; 0la7: M. tentorioglandularis, absent; 0la8: M. submentopraementalis (M28), one bundle, O: medially on the posterior region of the submentum, I: median fusion of palpigera; 0la9: M. postmentomembranus, absent; 0la10:M. submentomentalis, two bundles, O: tentorial bridge I: posterior margin of mentum; 0la11: M. praementoparaglossalis (M31): absent; 0la12: M. praementoglossalis (M32), absent; 0la13:M. praementopalpalis internus (M33), absent; 0la14:M.prae- mentopalpalis externus (M34), O: on the base of the palpiger between 0la8 and 0la9, I: posterobasal margin of palpomere 1; Fig. 5. A. juniperi, male, schematic drawing, main tracheal system, frontal view. Ab- 0la15: M. praementomembranus, absent; 0la16: M. palpopalpalis breviations: dtr e dorsal trachea, trant e trachea to the antenna, trc e tracheal labii primus (M35), O: mesal wall of palpomere 1, I: mesobasal commissure, trcpe e trachea to the compound eye, trlab e trachea to the labium, trmd margin of palpomere 2; 0la17: M. palpopalpalis labii secundus e trachea to the maxilla, trmx e trachea to the maxilla, trst e tracheal stems, vtr e ventral trachea. Arrows indicate the orientation of the head: A-P e anteroposterior (M36), O: on lateral wall of palpomere 2, close to its base; I: axis, L-R e left-right axis. Scale bar: 100 mm. mesobasal margin of palpomere 3. S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14 7

Fig. 6. Aleuropteryx, histological semithin sections. A, D, F Aleuropteryx sp., female, B, C Aleuropteryx loewii, male, E Aleuropteryx juniperi, male. AeD longitudinal sections, EeF cross sections. Abbreviations: acly e anteclypeus, amp e ampulla, ai e apical incisivus, ao e aorta, ata e anterior tentorial arm, bga e basigalea, br e brain, ca e cardo, car e cardinal ridge, cpe e compound eye, dga e distigalea, dta e dorsal tentorial arm, fb e fat body, fg e frontal ganglion, gu e gula, hypcg e hypocerebralganglion, hyph e hypopharynx, lbgl e labial gland, lbr e labrum, lig e ligula, md e mandible, mdgl e mandibular gland, mt e mentum, mxgl e maxiallary gland, nmx e maxillary nerve, nproc e nervus procurrens, nrec e nervus recurrens, oa e oral arm, ol e optic lobe, or e occipital ridge, pcly e postclypeus, ped e pedicellus, pg e palpiger, ph e pharynx, poccps e postoccipital sulcus, ppht e prepharyngeal tube, sai e subapical incisivus, sc e scapus, sd e salivary duct, slv e salivarium, smj e secondary mandibular joint, smt e submentum, soeg e sub- oesophagealganglion, sp e spur, st e stipes, tb e tentorial bridge, to e tormae, tr e temporal ridge, Musculature: 0ah2 e M. ampulloaortica, 0ah8 e M. ampullotentorialis, 0an1 e M. tentorioscapalis anterior, 0an2 e M. tentorioscapalis posterior, 0an3 e M. tentorioscapalis lateralis, 0an4 e M. tentorioscapalis medialis, 0an9 e M. scapopedicellaris posterior, 0bu1 e M. clypeobuccalis, 0bu2 e M. frontobuccalis anterior, 0bu5 e M. tentoriobuccalis anterior, 0bu6 e M. tentoriobuccalis posterior, 0ci1 e M. clypeopalatalis, 0hy1 e M. frontooralis, 0hy3 e M. craniohypopharyngalis, 0hy12 e M. hypopharyngosalivaris, 0hyx e intrinsic hypopharyngeal muscle, 0la10 e M. submentomentalis, 0la14 e M. frontooralis, 0lb2 e M. frontoepipharyngalis, 0md1a,b,c e M. craniomandibularis internus a,b,c, 0mx2 e M. craniolacinialis, 0mx3 e M. tentoriocardinalis, 0mx4a,b e M. tentoriostipitalis anterior a,b, 0mx6 e M. stipitolacinialis, 0mx7 e M. stipitogalealis, 0mx8 e M. stipitopalpalis externus, 0mx10 e M. stipitopalpalis internus, Ivlm1 e M. profurca-cervicalis, Ivlm3 e M. profurca- tentorialis. Scale bars: 100 mm. 8 S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14

3.8. Hypopharynx and salivary system passes through the frontal connectives, I: lateral precerebral pharyngeal wall anterior the ganglion frontale; 0bu3:M.fronto- The hypopharynx and the labrum form together a structural and buccalis posterior (M46), absent; 0bu4: M. tentoriobuccalis lat- functional unit. The anterior hypopharynx (Figs. 4A; 6B,C: hyph) is eralis (M49), absent; 0bu5: M. tentoriobuccalis anterior (M48), tongue-shaped in a larger median and two smaller lateral longi- medially on the fused dorsal tentorial arms with long tendon, I: tudinal folds. The tip of the tongue reaches the tip of the ligula; the ventral pharyngeal wall; 0bu6: M. tentoriobuccalis posterior hypopharyngeal cuticula is thickened but unsclerotized. The ante- (M50), O: fused dorsal tentorial arms medially to 0bu5, I: ventral rior hypopharynx is reinforced laterally by broad hypopharyngeal pharyngeal wall posterior to the insertion of 0bu5; 0ph1:M. suspensorial sclerites (Fig. 4A: hyssc). Their posterior margins are in verticopharyngalis (M51), absent; 0ph2: M. tentoriopharyngalis close contact with the internal mental ridges. The posterior hypo- (M52), absent; 0ph3: M. postoccipitopharyngalis, absent; 0st1:M. pharynx and the posterior epipharynx form a prepharyngeal tube annularis stomodaei (M68), pharyngeal ring musculature; 0st2: (Figs. 4B and 6C: ppht), which is reinforced by oral arms (Figs. 4A,B; M. longitudinalis stomodaei (M69), longitudinal muscles beneath 6B: oa) on both sides. Two salivary ducts (Figs. 4A and 6C: sd) enter 0st1 (Fig. 5). the head capsule and merge posterior to the tentorial bridge. The wall of the salivarium (Figs. 4A and 6F: slv) is sclerotized dorsally at the insertion site of 0hy12. 3.11. Nervous system Musculature (Figs. 4A; 6A,B,C,F). 0hy1: M. frontooralis (M41), O: medially on frons, anterior to origin of 0lb2, I: oral arm; 0hy2:M. The brain (Fig. 6B,C,E,F: br) and the suboesophageal ganglion tentoriooralis (M47), absent; 0hy3: M. craniohypopharyngalis (Fig. 6C,F: soeg) occupy about 30.5% of the head volume. The (M42), O: posterior margin of submentum and tentorial bridge, I: protocerebrum has a compact shape. The nervus procurrens on both sides of the anterior hypopharynx. 0hy4: M. post- (Fig. 6C: nproc) originates ventrally at the triangular frontal occipitalohypopharyngalis, absent; 0hy5: M. tentoriosuspensor- ganglion (Fig. 4B; 6C: fg) and innervates the cibarial and pre- ialis, absent; 0hy6: M. postmentoloralis, absent; 0hy7:M. pharyngeal dilator muscles (0ci1, 0bu1). The nervus recurrens praementosalivaris anterior (M38), O: lateral wall of palpiger, I: (Fig. 6C,E: nrec) originates dorsally on the frontal ganglion and lateral wall of salivarium; 0hy8 M. praementosalivaris posterior passes backwards along the pharynx to the hypocerebral ganglion (M39), O: lateral wall of palpiger, posterior to 0hy7, I: lateral wall of (Fig. 6C: hypcg). The frontal ganglion and the tritocerebrum are salivarium, posterior to 0hy7; 0hy9: M. oralis transversalis dorsalis linked by a pair of frontal connectives. The tritocerebral lobes are (M67), well-developed, O: anterior edge of oral arm, I: anterior connected by the tritocerebral commissure. Ocellar nerves and a edge of oral arm on the other side; 0hy10: M. loroloralis, absent; nervus connectivus are absent. The average diameter of the cell 0hy11: M. lorosalivarialis, absent; 0hy12: M. hypopharyngosalivaris bodies in the cell body rind of the superior lateral protocerebrum m ¼ m (M37), two bundles, O: posterior (A. juniperi) or anterior (A. loewii) is 2.66 m(n 36), the maximum is 3.87 mandtheminimum m oral arms, I: anterodorsal wall of salivarium; 0hy13: M. annularis size is 2.5 m. salivarii (M40), absent; 0hy14: M. submentosuspensorialis, absent; 0hy15: M. ducti salivarii, absent; 0hy16: M. oralis transversalis 3.12. Circulatory system ventralis, well-developed, O: posterior edge of oral arm, I: posterior edge of oral arm on the other side. A paired muscle with unclear The cephalic aorta (Fig. 6E: ao) is wide, approximately triangular homology (0hyx) runs from the ventral side of the prepharyngeal in cross-section and encloses the nervus recurrens. The ventral wall tube, just anterior to the insertion of 0bu5, to the anterior is very thin and hardly discernible. The paired and completely hypopharynx. separated antennal ampullae (Fig. 6C: amp) are close together and are located between the antennal foramina. Antennal vessels 3.9. Epipharynx originate from the ampullae laterally and extend into the antennae. Below the ampullae lie subampullar tissue masses. e The anterior epipharynx (Fig. 6A C) is membranous, only its Musculature (Fig. 6C). 0ah1: M. interampullaris, absent; 0ah2: anteriormost area is sclerotized. The posterior epipharynx and the M. ampulloaortica, in males one, in females two bundles, O: posterior hypopharynx form a prepharyngeal tube (Figs. 4B and 6C: antennal ampulla, I: dorsal wall of cephalic aorta; 0ah3:M. ppht). ampullopharyngalis, absent; 0ah4: M. ampullofrontalis anterior, Musculature (Figs. 4B; 6C). 0ci1: M. clypeopalatalis (M43), O: absent; 0ah5: M. frontopharyngalis, absent; 0ah6: M. fronto- medially on postclypeus, I: hind margin of anterior epipharynx frontalis, absent; 0ah7: M. ampullofrontalis lateralis, absent; 0ah8: between the tormae; 0bu1: M. clypeobuccalis (M44), O: post- M. ampullotentorialis, in males, O: antennal ampulla on both sides clypeus medially and posterior to 0ci1, I: anterior wall of the pre- of 0ah2, I: anterior area of dorsal tentorial arms vis a vis the pharyngeal tube between the bundles of 0hy9, anterior to the insertion of M. profurcatentorialis (Ivlm3). frontal ganglion.

3.10. Pharynx 3.13. Tracheal system

The anatomical opening of the mouth, defined as the insertion One large pair of tracheal stems (Fig. 5: trst) leads from the site of M. frontobuccalis anterior by Beutel et al. (2014), lies anterior thorax into the head capsule. The stems are connected by a tracheal to the ganglion frontale. The precerebral pharynx has a roundish commissure (Fig. 5: trc), it sends branches to the mandibular lumen and its wall is hardly pleated, while the wall of the post- muscles (Fig. 5: trmd), the tentorial pharyngeal muscles and the cerebral pharynx has many foldings and so constricts the lumen of posterior part of the brain. The tracheal stems branch into a dorsal the postcerebral pharynx (Figs. 4B; 6A,C,E,F: ph). M. longitudinalis and ventral trachea (Fig. 5: dtr, vtr). The dorsal trachea runs stomodaei is embedded in the folds. The dilator muscles insert at abruptly dorsally in front of the brain and splits into a trachea to the these folds. compound eye (Fig. 5: trcpe) and one to the antenna (Fig. 5: trant). Musculature (Figs. 4B; 6B,F). 0bu2: M. frontobuccalis anterior The ventral trachea bifurcates into a trachea to the labium (Fig. 5: (M45), O: medially on the frons below the antennal foramina, trlab) and another to the maxilla (Fig. 5: trmx). S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14 9

3.14. Glands (2009) and the absence of innervation observed in the present study exclude a sensory function. Males of several coniopterygid There are three exocrine glands in both sexes: paired mandib- species use their antennae to hold the female during mating ular glands in several tubes (Fig. 6D,F: mdgl), paired compact (Meinander, 1972), but this is unlikely in A. juniperi, because they maxillary glands (Fig. 6D,F: mxgl) and several wax glands (Fig. 2D). mate in a tail-to-tail position (Henry, 1976). The mandibular glands extend from the mandible to the optical A full set of four antennal muscles as in Aleuropteryx was lobes and open posterior to the primary mandibular joint into the recently described for C. pygmaea (Randolf et al., 2017) and seems mouth cavity. The smaller maxillary glands lie along the ventral rim to be a characteristic feature of the family Coniopterygidae. In other of the subgenae beneath the compound eyes and open laterally to neuropteran families, the M. tentorioscapalis lateralis (0an3) is the articulation site of the cardo. Wax glands are situated on the reduced (Zimmermann et al., 2011). The presence of four scapo- scapus and several wax glands on the head capsule between the pedicellar muscles, however, is documented for all neuropteran antennal foramina. The opening of the wax gland is roundish in families in which it has been studied (Miller, 1933; Randolf et al., both sexes. It should be noted that the labial glands (Fig. 6A,F: lbgl) 2013, 2014, 2017). protrude, in females more than in males, from the thorax into the Prominent temporal sulci run between the dorsolateral angles head capsule. of the occipital foramen and the rims of the eyes, whereas in other insects they are convergent between the eyes (Snodgrass, 1960). 3.15. Fat body The postocciput is deeply inflected and covered by folds of the cervical membrane (Shepard, 1967; Randolf et al., 2013, 2014, A compact fat body (Fig. 6C: fb) is mainly located in the frontal 2017). region and above the brain. 4.1.2. Mouthparts 4. Discussion Although the mouthparts of Aleuropteryx are small and lie far anteriorly compared to other Neuroptera, their morphology cor- 4.1. General morphology responds to the ground pattern of Neuroptera outlined by Shepard (1967). The mandibles are asymmetrical, have a molar process and 4.1.1. Head and antennae lack a grinding surface. Unlike in C. pygmaea, subapical incisors are All hitherto described subforaminal bridges (sensu Burks and developed in addition to the apical incisors. Heraty, 2015) between the mouthparts and the occipital foramen Maxillae and labium are well-developed and connected by in Neuroptera are hypostomal bridges, formed by the hypostoma membrane. A semicircular process of the cardo that articulates with and situated anteriorly to the posterior tentorial pits (Morse, 1931; the hypostomal bridge was newly described for Neuroptera in Ferris, 1940; Shepard, 1967; Acker, 1958; Krenn et al., 2008: Fig. 7; C. pygmaea. Also in Aleuropteryx, the process of the cardo is semi- Randolf et al., 2017). In Aleuropteryx the subforaminal bridge was circular, albeit less pronounced, but it articulates with the tentorial also interpreted as a hypostomal bridge (Zimmermann et al., 2009; bridge. In other Neuroptera, the protrusions of the cardo are less Beutel et al., 2014), but the present investigation revealed that it is distinct and articulate with the head capsule (Sundermeier, 1940; in fact a formation of the neck, a gula (sensu Snodgrass, 1935). Beutel et al., 2010; Randolf et al., 2014). Likewise, an almost upright position of the tentorium with As in C. pygmaea, M. stipitopalpalis medialis (0mx9) is present in posterior tentorial pits that lie far anteriorly is not known in any Aleuropteryx. It has recently been described for Sisyra (Randolf et al., other Neuroptera. Dorsal tentorial arms, if present, are more or less 2013) but is otherwise not known from adult Neuroptera (Randolf well developed in several neuropteran families (Zimmermann et al., 2014, 2017). et al., 2011) but never fused to an arch as in Aleuropteryx. Con- Remarkably, the galea of Aleuropteryx is divided into a basigalea, cerning the musculature, the dorsal tentorial arms take the func- a distigalea and a finger-like process of the galea as in certain other tion of the tentorial bridge in Aleuropteryx: various tentorial neuropteran families (Tjeder, 1957,1959; 1960; Randolf et al., 2014). muscles, such as M. tentoriobuccalis anterior (0bu5) and M. ten- In contrast, the galea of C. pygmaea is composed of a distigalea and a toriobuccalis posterior (0bu6), usually originate on the tentorial finger-like process, while a basigalea is missing (Randolf et al., bridge in Neuroptera (Miller, 1933; Korn, 1943; Beutel et al., 2010; 2017). Randolf et al., 2013, 2014, 2017). In Aleuropteryx, however, they Internal mental ridges that are in close contact with the hypo- attach to the dorsal tentorial arms. Likewise, the insertion of the pharyngeal suspensorial sclerites have recently been described for thoracical muscle M. profurcatentorialis (Ivlm3), which usually lies C. pygmaea (Randolf et al., 2017) but are not known from other on the tentorial bridge in Neuroptera, is shifted to the dorsal ten- Neuroptera (Beutel et al., 2010; Randolf et al., 2013, 2014). As they torial arms in Aleuropteryx. The antennal heart muscle M. ampul- are also present in Aleuropteryx, they could be a family-specific lotentorialis (0ah8), known only from males of Coniopterygidae, feature. inserts on the tentorial bridge in the Coniopteryginae species In several neuropteran families, the ligula is covered only C. pygmaea and on the dorsal tentorial arms in the two investigated proximally by the hypopharynx and the salivary opening itself does Aleuropteryginae species. not reach the tip of the ligula (Sulc, 1914: Fig. 19; Randolf et al., A division of the clypeus into an anteclypeus without, and a 2013: Fig. 8; Randolf et al., 2014: Fig. 7). Furthermore, paraglossae postclypeus with muscle origin (Matsuda, 1965) is unique in are folded onto the ligula and form, together with the ligula, a Aleuropteryx; in all hitherto described Neuroptera, the clypeus is secondary prolongation of the salivary opening to the tip of the undivided (Morse, 1931; Korn, 1943: Fig. 16; Beutel et al., 2010; ligula. This formation was interpreted as an adaptation to feeding Randolf et al., 2013, 2014, 2017). not only on liquid, but also on desiccated honeydew by applying A varying number of flagellomeres within a species, or even saliva directly to the leaf surface to liquefy it (Randolf et al., 2013). between left and right antennae of the same specimen, is a com- Adults of Aleuropteryx also feed on secretions of scale insects: when mon feature for Coniopterygidae (Meinander, 1972). A ventral spine running along branches that are infested by scale insects, they often on the pedicel of the male is a characteristic trait for the genus stop and appear to feed on the crystal-like substance that coats Aleuropteryx (Low,€ 1885), though its function remains unclear: The many of the shrubs (Henry, 1976). Paraglossae are absent in Aleur- lack of microtrichia or sensilla pointed out by Zimmermann et al. opteryx, but the hypopharynx itself reaches to the tip of the ligula, 10 S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14

Fig. 7. Coniopterygidae, volume rendering of the head with 3D-reconstructions of the tentorium and the subforaminal bridges. A A. juniperi,BC. pygmaea. Abbreviations: ata e anterior tentorial arm, atp e anterior tentorial pit, dta e dorsal tentorial arm, gu e gula, hystb e hypostomal bridge, ptp e posterior tentorial pit. Scale bars: 100 mm.

thus forming a prolongation that enables optimal exploitation of the intrinsic muscle is uncertain; it is possibly an anteriorly shifted this food source. M. longitudinalis stomodaei. In all adult Neuroptera studied to date, the M. sub- mentomentalis (0la10) is documented (Das, 1937; Korn, 1943; 4.1.4. Circulatory system Beutel et al., 2010: described as M. submentopraementalis but As in C. pygmaea, the circulatory system of Aleuropteryx is also with insertion on the posteromedian mental margin; Randolf et al., sexually dimorphic: A M. ampulloaortica (0ah2) is present in both 2013, 2014). An additional muscle with an origin at the sub- sexes, and has also been documented as dilator muscle of the mentum, the M. submentopraementalis (0la8), was reported for antennal heart in other Neuroptera (Randolf et al., 2014, 2017). As in C. pygmaea and is also present in Aleuropteryx, whereas it is absent C. pygmaea, however, a second muscle originating on the tentorium in all other studied Neuroptera (Das, 1937; Korn, 1943; Beutel et al., (0ah8) is present in males. This muscle has not yet been described 2010, see above; Randolf et al., 2013, 2014). in other insects. Several muscles of the mouthparts are absent in Aleuropteryx: There are only two other studies describing the antennal heart the absence of M. frontolabralis (0lb1) is correlated with the muscles in both sexes. Both found no differences between females shape of the anteclypeus, which partly overlaps the labrum and and males (Pass, 1980; Randolf et al., 2014). Thus, there are insuf- thus hampers its upward movement. The absence of the ficient data to answer the question whether this sexual dimor- mandibular adductor M. tentoriomandibularis lateralis inferior phism is a widespread phenomenon in insects or unique for (0md6), which is present in most larger relatives, as well as in the Coniopterygidae. miniaturized C. pygmaea (Zimmermann et al., 2011; Randolf et al., 2017), is presumably compensated by the massive main adductor 4.1.5. Glands M. craniomandibularis internus (0md1). The absence of M. Mandibular glands are described for all hitherto investigated praementopalpalis internus (0la13) is also not unexpected, as it Neuroptera and can be divided into two structurally different types: can also be absent in larger relatives (Randolf et al., 2014). In all compact glands as in Sisyra and Nevrorthus (Randolf et al., 2013, hitherto investigated Neuroptera, M. craniocardinalis (0mx1) is 2014) and tube-like glandular lobes as in Osmylus (Beutel et al., present (Miller, 1933; Korn, 1943; Beutel et al., 2010, Randolf et al., 2010) and Coniopteryx (Randolf et al., 2017). The mandibular 2013, 2014, 2017). Its absence in Aleuropteryx is difficult to gland of Aleuropteryx is of the tube-like type. interpret. 4.2. Effects of miniaturization 4.1.3. Hypopharynx and salivary system A hypopharynx that is laterally reinforced by solid hypophar- The most striking feature in Coniopterygidae is their small yngeal suspensorial plates and has well-developed oral arms agrees body size. Previous works have shown that the main effects of with the findings in most other Neuroptera (Shepard, 1967; Randolf miniaturization are reductions, structural simplifications and et al., 2013, 2014). In addition, the muscular arrangement conforms morphological novelties (Hanken and Wake, 1993; Beutel and to what is found in most other Neuroptera: M. craniohypophar- Haas, 1998; Polilov, 2005; Polilov and Beutel, 2009, 2010; yngalis (0hy3) originates, in Aleuropteryx at least partly, on the Polilov, 2011; Schneeberg et al., 2013; Polilov, 2015a, b; Knauthe tentorium and inserts on the lateral hypopharyngeal suspensorial et al., 2016; Polilov and Shmakov, 2016; Yavorskaya and Polilov, plates or laterally at the base of the hypopharynx (Korn, 1943; 2016; Yavorskaya et al., 2018). Miniaturization effects in Randolf et al., 2013, 2014). Coniopterygidae have already been reported for various parts of The intrinsic muscle of the hypopharynx (0hyx) has been pre- their body, e.g., simplified wing venation (Enderlein, 1906), fewer viously described for C. pygmaea (Randolf et al., 2017) and is Malpighian tubules, ovaries dislocated into the metathorax, and a apparently absent in other investigated adult Neuroptera. Intrinsic reduced number of abdominal ganglia (Withycombe, 1925). Our muscles of the prepharynx are described only for the larvae of results also reveal profound modifications e reductions, structural Euroleon nostras (Korn, 1943: “Eigenmuskeln”). The homology of simplifications and morphological novelties e in the cephalic S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14 11 anatomy. Furthermore, we found another effect that has been The brain in Aleuropteryx is not dumbbell-shaped and lacks the pointed out by Hanken and Wake (1993) but not yet documented distinct optic lobes typical for Pterygota and larger Neuroptera for insects: the comparison of the present results with those on (Beutel et al., 2010; Randolf et al., 2013, 2014). A slight decrease in the Coniopteryginae C. pygmaea (Randolf et al., 2017) shows a the relative volume of the optic lobes areas that function in coor- higher morphological variability in Coniopterygidae than in dination and in processing sensory signals (optic and antennal Neuropteran families with a larger body size (Randolf et al., 2013, lobes) is a common trend in microinsects (Makarova and Polilov, 2014; Chrysopidae, Hemerobiidae, Dilaridae pers. obs.). 2013a, b) and has also been observed in C. pygmaea (Randolf et al., 2017), Coleoptera and Hymenoptera. These sensory centers 4.2.1. Reduction and simplification can be smaller because the number of facets is also reduced in small insects (Makarova and Polilov, 2013a, b). 4.2.1.1. Cephalic skeleton. Simplification of the cephalic skeleton up Furthermore, the minimum cell body size of 2.5 mminAleuro- to the complete absence of sulci is a general trend in microinsects pteryx is clearly smaller than in larger relatives (e.g. Nevrorthus (Polilov and Beutel, 2009, 2010; Polilov, 2016c; Randolf et al., 2017; apatelios: ca. 5 mm, see Randolf et al., 2014: Fig. 8) and similar to the Yavorskaya et al., 2018) and can also be observed in Aleuropteryx cell body size reported for C. pygmaea (Randolf et al., 2017). A where much fewer sulci are visible externally than in larger Neu- reduced cell body diameter is a well-known effect of miniaturiza- roptera (Morse, 1931; Ferris, 1940; Sundermeier, 1940; Shepard, tion (Beutel and Haas, 1998; Beutel et al., 2005; Makarova and 1967; Beutel et al., 2010; Randolf et al., 2013, 2014). Polilov, 2013a, b). The decrease in cell size may reflect the reduced volume of the cytoplasm or an increase in the chromatin 4.2.1.2. Compound eyes. Reductions in the number and the compaction level (Makarova and Polilov, 2013a, b). diameter of the facets, and a countersunk ocular ridge are described for several miniaturized insects (Partmann, 1948; Honkanen and 4.2.1.4. Musculature. The restricted space in the head capsule also Meyer-Rochow, 2009: Fig. 5; Polilov and Beutel, 2009: Fig. 13C, D; affects the total number of muscles in Aleuropteryx. It is clearly Fischer et al., 2012a: Fig. 6A,B; 2012b; 2014: Fig. 4; Makarova et al., lower than in the larger relatives Sisyra terminalis and N. apatelios 2015: Fig. 4A, Randolf et al., 2017). That makes the eyes of Aleuro- (A. juniperi:44,S. terminalis: 54, N. apatelios: 50; see Randolf et al., fl pteryx at and not protruding in contrast to those of larger 2017). As in C. pygmaea (Randolf et al., 2017), the pharyngeal Neuroptera (Beutel et al., 2010: Fig. 2a, c, d; Randolf et al., 2013: muscles are most strongly affected by reductions: five dilator Fig. 3a, b; Randolf et al., 2014: Fig. 3a, b). The ocular ridge is muscles of the prepharyngeal and pharyngeal tube, usually present countersunk into the head capsule as in C. pygmaea (Randolf et al., in larger Neuroptera (Miller, 1933; Korn, 1943; Beutel et al., 2010; 2017), whereas it is approximately planar in non-miniaturized Randolf et al., 2013, 2014), are absent in Aleuropteryx. Reductions Neuroptera (Beutel et al., 2010: Fig. 8c; Randolf et al., 2013: of the musculature of the alimentary tract are also reported in other Fig. 9b; Randolf et al., 2014: Fig. 8c). This shape of the ocular ridge miniaturized insects, e.g. in Coleoptera, Diptera and Thysanoptera gives the light-sensitive part of the photoreceptor enough space to (Grebennikov and Beutel, 2002; Polilov and Beutel, 2009; maintain the photoreceptive ability (Fischer et al., 2011). Schneeberg et al., 2013; Polilov and Shmakov, 2016). Since the size of the digestive system changes isometrically with total body 4.2.1.3. Nervous system. Conspicuously large parts of the head size (Polilov, 2008), the remaining dilators and contractors of the capsule of Aleuropteryx are filled with brain tissue, and the nerves pharyngeal ring muscles, in combination with the longitudinal have a larger diameter in relation to the head size than those of musculature of the pharynx, probably suffice to transport food other neuropteran families. This corresponds with findings in other through a particularly narrow tube. miniaturized insects: the volume of the nervous system relative to Generally, the degree of reduction of musculature is low and the head and body volume increases allometrically (Rensch, 1948; does not follow a common pattern in microinsects (Beutel and Goossen, 1949; Beutel and Haas, 1998; Beutel et al., 2005; Polilov, Haas, 1998; Grebennikov and Beutel, 2002; Polilov, 2005, 2016c, 2005, 2008; Polilov and Beutel, 2009; Schneeberg et al., 2013; 2008; Polilov and Beutel, 2009, 2010; Schneeberg et al., 2013; Polilov, 2015a, b; Polilov and Makarova, 2017; Randolf et al., Polilov and Shmakov, 2016; Yavorskaya and Polilov, 2016; Randolf 2017). Beutel and Haas (1998) pointed out that the control and et al., 2017). the signal processing functions of the brain require a certain number of neurons, so that the size-reduction of the brain cannot 4.2.1.5. Tracheal system. Simplified tracheal systems are a previ- go beyond a minimum. There are manifold ways to cope with this ously reported effect of miniaturization (Polilov and Beutel, 2009; problem. Polilov and Beutel, 2010; Knauthe et al., 2016; Polilov, 2016a, b, c; One strategy of miniaturized insects to cope with the resulting Polilov and Shmakov, 2016; Randolf et al., 2017). In Aleuropteryx, lack of space is to pack nervous tissues very tightly (Beutel and only one connected pair of tracheal stems enters the head capsule, Haas, 1998). This is also the case in Aleuropteryx. Another solution whereas there are two separate pairs in the larger neuropteran is to dislocate parts of the brain, e.g. into the thorax (larvae: families (Beutel et al., 2010; Sisyra, Nevrorthus pers. obs.). This is Grebennikov and Beutel, 2002; Beutel and Hornschemeyer,€ 2002; correlated with the different surface-to-volume ratios in structures Beutel et al., 2005; Polilov and Beutel, 2009; Knauthe et al., 2016; of different sizes: the smaller the structure, specifically the nerve or larvae and adults: Polilov and Beutel, 2010; Yavorskaya et al., 2018) muscle bundle, the larger the surface in relation to the volume, or even into the coxae (larvae: Polilov and Shmakov, 2016). This which in turn increases the area over which oxygen can diffuse into strategy can be observed in larvae of Coniopterygidae (Rousset, the tissue (Niven and Farris, 2012). Consequently, miniaturized 1966), but is not an option for adults, where the constricted neck species require less extensive oxygen supply networks than larger region, the narrowed occipital foramen, and the need for a high relatives, and the tracheal system can be simplified or even mobility of the head impede a dislocation of the brain into the reduced. thorax. A unique strategy to master the lack of space in the head capsule is followed by the tiny hymenopteran Megaphragma 4.2.2. Morphological novelties mymaripenne, where the volume of the brain in adults is consid- 4.2.2.1. Gula. The closure of the occipital foramen by a gula in erably decreased through lysis of more than 95% of the nuclei and Aleuropteryx is a morphological novelty and unique in Neuroptera. cell bodies of pupal neurons (Polilov, 2012). Modifications in the posterior ventral parts of the head are 12 S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14 generally associated with a prognathous condition (Snodgrass, 4.2.3. Increased morphological variability 1935). The formation of a gula in the orthognathous head of The high divergence that was described for the external Aleuropteryx may be related to the size of the suboesophageal morphology of the two subfamilies Coniopteryginae and ganglion and the need for muscular attachment sites on the pos- Aleuropteryginae (Meinander, 1972) is also reflected in the cephalic terior ventral region of the head capsule. In larger Neuroptera, the anatomy. The subforaminal bridges have different origins (Fig. 7) suboesophageal ganglion is relatively small in relation to the head and the tentoria have strikingly different forms: in Coniopteryx capsule and situated above the submentum. In Aleuropteryx, this without dorsal tentorial arms or a median process, and with pos- ganglion is distinctly more voluminous and fills almost the whole terior tentorial pits laterally of the occipiptal foramen (Randolf space beneath the pharynx. A gula and anteriorly shifted mouth- et al., 2017), and in Aleuropteryx with fused dorsal tentorial arms, parts could help protect against damage to the suboesophageal a well developed process and far anteriorly positioned posterior ganglion through mouthparts movements. tentorial pits. In correlation with these differences, several muscles of the pharynx, the antennal heart and thoracic musculature have different origins or insertions in the two subfamilies. 4.2.2.2. Structure of tentorium. The formation of a gula causes an A variation concerning the origins is evident even on a species upright position of the tentorium with a tentorial bridge that lies far level: in A. juniperi, the M. hypopharyngosalivaris (0hy12) origi- anteriorly and thus cannot fulfill the function of an attachment nates at the posterior region of the oral arms, whereas in A. loewii it structure for several muscles. In Aleuropteryx, the situation is originates at the anterior region of the oral arms. resolved by fusing the dorsal tentorial arms into an arch that takes The hypopharyngeal sclerites and the course of the hypophar- the function of the tentorial bridge. This is a new formation which yngeal muscles also differ considerably between the two sub- is, based on our review of the literature, not known in other insect families: in C. pygmaea the lateral hypopharyngeal suspensoria are orders (Yuasa, 1920; Snodgrass, 1935; Hudson, 1945, 1947; 1948, continuously slender bars and an additional rectangular transverse 1951; Matsuda, 1965; Beutel and Lawrence, 2005; Klass and bar lies posteriorly on the anterior hypopharynx, bearing the Eulitz, 2007; Beutel et al., 2014; Zimmermann and Vilhelmsen, insertion of M. tentoriosuspensorialis (0hy5), a muscle missing in 2016). Aleuropteryx. Furthermore, in C. pygmaea M. craniohypopharyngalis (0hy3) runs from the submentum to the roof of the anterior hy- popharynx (Randolf et al., 2017); in Aleuropteryx it inserts on both 4.2.2.3. Glands. Wax glands occur only in Coniopterygidae and are sides of the anterior hypopharynx. The mandibles vary as well: only thus a morphological novelty of this family. Within a short time, in Aleuropteryx are subapical incisors developed in addition to the newly emerged adults start to secrete the wax and continue to do apical incisors. so throughout most of their life (Withycombe, 1925). Wax glands Zimmermann et al. (2009) and Randolf et al. (2017) pointed out are primarily located on the abdomen, rarely on the scape and head that the shape of the opening of the wax glands is a subfamily- (Nelson et al., 2003). The fore- and hind legs are used to spread the specific character: the opening of the wax gland is four-leafed wax all over the body (Johnson, 1980; Nelson et al., 2003). Wax- clover-shaped in Coniopteryginae, and roundish with seaming producing glands are also known from small-bodied hemipteran rings in Aleuropteryginae. Variations in the morphology of the wax species. There, the wax layer is believed to provide protection gland openings among various species are also reported for wax- against UV radiation, rain and contamination with honeydew secreting Hemiptera, where different pore types occur even (Retnakaran et al., 1979; Kumar et al., 1997; Smith, 1999; Nelson within one specimen (Pope, 1983; Ammar et al., 2013), which might et al., 2000; Lucchi and Mazzoni, 2004; Ammar et al., 2013). Hon- be another case of increased variability due to miniaturization. eydew is dangerous for insects because it promotes microbial In larger Neuroptera in which more than one species or both growth that can ultimately lead to suffocation (Elton, 1958; Mittler sexes were investigated (Randolf et al., 2013, 2014; Chrysopidae, and Douglas, 2003). In addition, the wax layer protects against Hemerobiidae, Dilaridae pers. obs.), neither sex-, nor species- desiccation (Smith, 1999), a condition that miniaturized forms are specific differences in the head morphology were observed. especially vulnerable to, because the surface-to-volume ratio is higher in small bodies (Neville, 1998). 5. Concluding remarks Maxillary glands are not described in any other neuropteran. Voluminous paired maxillary glands also occur in Protura, where The cephalic morphology of Aleuropteryx is highly affected by they lead into the preoral cavity on the inner side of the lacinia miniaturization. Our results demonstrate manifold ways in which (François and Dallai, 1986); small glands opening into the space structural modifications e specifically reductions, structural sim- occupied by the mandibular and maxillary stylets are reported for plifications and morphological novelties e compensate effects of some Heteroptera (Linder, 1956) and are also known for Collembola size decrease in Coniopterygidae. The striking differences between (Snodgrass, 1935) and Coleoptera (Pradhan, 1939). Their function Aleuropteryx and the previously studied C. pygmaea illustrate the remains unclear. They have been hypothesized to have a digestive predicted increase of variability in miniaturized forms for the first function, to provide secretions for lubricating the mouthparts or to time in insects. This raises the question, whether the internal secrete pheromones (François and Dallai, 1986). In Aleuropteryx,a morphology of singular small representatives from larger function as an additional gland with lubricating function seems neuropteran families also diverges as strongly. This would reveal an more plausible than a pheromone gland; the fact that the gland unexpected intrafamiliar diversity in other families as well. occurs in both sexes is not in line with the observations on the reproductive biology of this genus, in which receptive females Acknowledgements apparently release a pheromone to attract males (Henry, 1976). Indeed they feed on scale insects, but only the soft-bodied younger We are grateful to Barbara Schadl€ (Ludwig Boltzmann Institute stages are grasped with the mandibles and consumed completely, for Experimental and Clinical Traumatology) for the excellent while in mature scale insects they chew off the hard shell and feed semithin-sections, Harald Bruckner (Natural History Museum only on the soft-bodied internal parts (Henry, 1976). Thus, an Vienna) for photographing the histological sections, Mika Wohl- additional digestive function for hard-to-digest pieces does not genannt (Sir Karl Popper Schule, Vienna) for reconstructions in seem necessary. Amira during his internship (FFG Nr. 17079463/867614), as well as S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14 13

Alice Laciny, Sabine Gaal-Haszler (Natural History Museum Vienna) position of Ptiliidae (Coleoptera: Staphylinoidea). Arthropod Struct. Dev. 31, e and Michael Stachowitsch (University of Vienna) for linguistic im- 157 172. € Hanken, J., Wake, D.B., 1993. Miniaturization of body size: organismal consequences provements of the manuscript. We sincerely thank Ulrike Aspock and evolutionary significance. Annu. Rev. Ecol. Systemat. 24, 501e519. (Natural History Museum Vienna) for determining the males of Henry, T.J., 1976. Aleuropteryx juniperi: a European scale predator established in Aleuropteryx to species level and Hubert Rausch (Scheibbs) for North America (Neuroptera: Coniopterygidae). Proc. Entomol. Soc. Wash. 78, 195e201. providing one A. juniperi male. We thank Kerry S. Matz (Salt Lake Honkanen, A., Meyer-Rochow, V.B., 2009. The eye of the parthenogenetic and City, Utah, USA) for enriching our publication with his image of a minute moth Ectoedemia argyropeza (Lepidoptera: Nepticulidae). Eur. J. Ento- living Aleuropteryx sp. This research was supported using resources mol. 106 (4), 619e629. Hudson, G.B., 1945. A study of the tentorium in some orthopteroid Hexapoda. of the VetCore Facility of the University of Veterinary Medicine J. Entomol. Soc. South Afr. 8, 71e90. Vienna (microCT facility, operated by Stephan Handschuh). Last but Hudson, G.B., 1947. Studies in the comparative anatomy and systematic importance not least, we appreciate the suggestions of the reviewers, which of the hexapod tentorium. II. Dermaptera, Embioptera and Isoptera. J. Entomol. Soc. South Afr. 9, 99e110. helped to further improve the manuscript. Hudson, G.B., 1948. Studies in the comparative anatomy and systematic importance of the hexapod tentorium III. Odonata and Plecoptera. J. Entomol. Soc. South Afr. 11, 38e49. Hudson, G.B., 1951. Studies in the comparative anatomy and systematic importance References of the hexapod tentorium. IV. Ephemeroptera. J. Entomol. Soc. South Afr. 14, 3e23. Acker, T.S., 1958. The comparative morphology of Stenorrhachus walkeri Johnson, V., 1980. Review of the Coniopterygidae (Neuroptera) of North America (MacLachlan) and of Nemopterella sp. (Neuroptera: Nemopteridae). Micro- with a revision of the genus Aleuropteryx. Psyche 87, 259e298. entomology 23, 106e130. Johnson, V., Morrison, W.P., 1979. Mating behavior of three species of Ammar, E.-D., Alessandro, R., Shatters Jr., R.G., Hall, D.G., 2013. Behavioral, ultra- Coniopterygidae (Neuroptera). Psyche 86, 395e398. € structural and chemical studies on the honeydew and waxy secretions by von Keler, S., 1963. Entomologisches Worterbuch. Akademie Verlag, Berlin. nymphs and adults of the Asian Citrus Psyllid Diaphorina citri (Hemiptera: Klass, K.D., Eulitz, U., 2007. The tentorium and anterior head sulci in Dictyoptera Psyllidae). PLoS One 8 (6), e64938. and Mantophasmatodae (Insecta). Zool. Anz. 246, 205e234. € Beutel, R.G., Friedrich, F., Ge, S.-Q., Yang, X.-K., 2014. Insect Morphology and Phy- Klapalek, F., 1894. Is Aleuropteryx lutea,Low, identical with Coniopteryx lutea Wallg. logeny: A Textbook for Students of Entomology. Walter de Gruyter, Berlin/ Entomol. Month Mag. 30, 121e122. Boston. Kleinteich, T., Beckmann, F., Herzen, J., Summers, A.P., Haas, A., 2008. Applying X- Beutel, R.G., Haas, A., 1998. Larval head morphology of Hydroscapha natans (Cole- ray tomography in the field of vertebrate biology: form, function, and evo- optera, Myxophaga) with reference to miniaturization and the systematic po- lution of the skull of caecilians (Lissamphibia: Gymnophiona). In: Stock, S.R. sition of Hydroscaphidae. Zoomorphology 118, 103e116. (Ed.), Developments in X-Ray Tomography VI. Proceedings of SPIE 7078D, Beutel, R.G., Hornschemeyer,€ T., 2002. Larval morphology and phylogenetic position pp. 1e11. € of Micromalthus debilis LeConte (Coleoptera: Micromalthidae). Syst. Entomol. 27 Knauthe, P., Beutel, R.G., Hornschemeyer, T., Pohl, H., 2016. Serial block-face scan- (2), 169e190. ning electron microscopy sheds new light on the head anatomy of an extremely Beutel, R.G., Lawrence, J.F., 2005. Coleoptera, morphology. In: Beutel, R.G., miniaturized insect larva (Strepsiptera). Arthropod Syst. Phylogeny 74 (2), Leschen, R.A.B. (Eds.), Handbook of Zoology, Arthropoda: Insecta; Coleoptera, 107e126. Beetles, Volume 1: Morphology and Systematics (Archostemata, Adephaga, Korn, W., 1943. Die Muskulatur des Kopfes und des Thorax von Myrmeleon euro- Myxophaga, Polyphaga Partim). Walter de Gruyter, Berlin/Boston, pp. 23e28. paeus und ihre Metamorphose. Zool. Jahrb. Abt. Anat. Ontog. Tiere 68, 273e330. Beutel, R.G., Pohl, H., Hünefeld, F., 2005. Strepsipteran brains and effects of mini- Krenn, H.W., Gereben-Krenn, B.A., Steinwender, B.M., Popov, A., 2008. Flower aturization (Insecta). Arthropod Struct. Dev. 34 (3), 301e313. visiting Neuroptera: mouthparts and feeding behaviour of Nemoptera sinuata Beutel, R.G., Zimmermann, D., Krauß, M., Randolf, S., Wipfler, B., 2010. Head (Nemopteridae). Eur. J. Entomol. 105, 267e277. morphology of Osmylus fulvicephalus (Osmylidae, Neuroptera) and its phylo- Kristensen, N.P., Nielsen, E.S., 1979. A new subfamily of micropterigid moths from genetic implications. Org. Divers. Evol. 10, 311e329. South America. A contribution to the morphology and phylogeny of the Brown, B.V., 1993. A further chemical alternative to critical-point-drying for pre- Micropterigidae, with a generic catalogue of the family (Lepidoptera: paring small (or large) flies. Fly Times 11, 10. Zeugloptera). Steenstrupia 5, 69e147. Burks, R.A., Heraty, J.M., 2015. Subforaminal bridges in Hymenoptera (Insecta), with Kumar, V., Tewari, S.K., Datta, R.K., 1997. Dermal pores and wax secretion in a focus on Chalcidoidea. Arthropod Struct. Dev. 44, 173e194. mealybug Maconellicoccus hirsutus (Hemiptera, Pseudococcidae), a pest of Carpentier, F., Lestage, J.A., 1928. Une sous-famille nouvelle (Fontenelleinae) du mulberry. Ital. J. Zool. 64, 307e311. groupe des Coniopterygoidea till. Recueil Inst Zool Torley Rousseau 1, 153e172. Linder, H.J., 1956. Structure and histochemistry of the maxillary glands in the Das, G.M., 1937. The musculature of the mouth-parts of insect larvae. Q. J. Microsc. milkweed bug, Oncopeltus fasciatus (Hem.). J. Morphol. 99, 575e611. € Sci. 80, 39e80. Low, F., 1885. Beitrag zur Kenntniss der Coniopterygiden. Sitzungsber Kaiserl Akad Elton, C.S., 1958. The Ecology of Invasions by Animals and Plants. Springer, US. Wiss Math Naturwiss Cl Abt 1 91, 73e89. Enderlein, G., 1906. Monographie der Coniopterygiden. Zool. Jahrb. Abt. Syst. Oekol. Lucchi, A., Mazzoni, E., 2004. Wax production in adults of planthoppers (Homo- Geogr. Tiere 23, 173e242. ptera: Fulgoroidea) with particular reference to Metcalfa pruinosa (Flatidae). Ferris, G.F., 1940. The morphology of Plega signata (Hagen) (Neuroptera: Man- Ann. Entomol. Soc. Am. 97, 1294e1298. tispidae). Microentomology 5, 33e56. Makarova, A.A., Polilov, A.A., 2013a. Peculiarities of the brain organization and fine Fischer, S., Meyer-Rochow, V.B., Müller, C.H.G., 2012a. Challenging limits: ultra- structure in small insects related to miniaturization. 1. The smallest Coleoptera structure and size-related functional constraints of the compound eye of Stig- (Ptiliidae). Zool. Zh. 92 (5), 523e533 [Entomol Rev 93(6), 703e713]. mella microtheriella (Lepidoptera: Nepticulidae). J. Morphol. 273, 1064e1078. Makarova, A.A., Polilov, A.A., 2013b. Peculiarities of the brain organization and fine Fischer, S., Meyer-Rochow, V.B., Müller, C.H.G., 2014. Compound Eye Miniaturization structure in small insects related to miniaturization. 2. The smallest Hyme- in Lepidoptera: a comparative morphological analysis. Acta Zool. 95 (4), noptera (Mymaridae, Trichogrammatidae). Zool. Zh. 92 (6), 695e706 [Entomol 438e464. Rev 93(6), 714e724]. Fischer, S., Müller, C.H.G., Meyer-Rochow, V.B., 2011. How small can small be: the Makarova, A., Polilov, A., Fischer, S., 2015. Comparative morphological analysis of compound eye of the parasitoid wasp Trichogramma evanescens (Westwood, compound eye miniaturization in minute Hymenoptera. Arthropod Struct. Dev. 1833) (Hymenoptera, Hexapoda), an insect of 0.3- to 0.4-mm total body size. 44 (1), 21e32. Vis. Neurosci. 28 (4), 295e308. Matsuda, R., 1965. Morphology and evolution of the insect head. Mem. Am. Ento- Fischer, S., Müller, C.H.G., Meyer-Rochow, V.B., 2012b. Neither apposition nor su- mol. Inst. (Gainesv.) 4, 1e334. perposition: the compound eyes of the chestnut leafminer Cameraria ohridella. Meinander, M., 1972. A revision of the family Coniopterygidae (Planipennia). Acta Zoomorphology 131, 37e55. Zool. Fenn. 136, 1e357. François, J., Dallai, R., 1986. Ultrastructure des glandes maxillaires d'Acerentomon Miller, F.W., 1933. Musculature of the lacewing (Chrysopa plorabunda) Neuroptera. affine Badn. et d'Eosentomon transitorium Berl. (Apterygota: Protura). Int. J. In- J. Morphol. 55, 29e51. sect Morphol. Embryol. 15, 201e212. Mittler,T.E., Douglas, A.E., 2003. Honeydew. In: Resh, V.H.,Carde, R.T. (Eds.), Encyclopedia Friedrich, F., Beutel, R.G., 2008. The thorax of Zorotypus (Hexapoda, Zoraptera) and a of Insects. Academic Press, Elsevier Science, New York, Amsterdam, pp. 523e526. new nomenclature for the musculature of Neoptera. Arthropod Struct. Dev. 37, Morse, M., 1931. The external morphology of Chrysopa perla L. (Neuroptera: 29e54. Chrysopidae). J. N. Y. Entomol. Soc. 39, 1e43. Gepp, J., 1967. Die Coniopterygidae des Grazer Feldes und seiner Randgebiete. Mitt Muma, M.H., 1967. Biological notes on Coniopteryx vicina (Neuroptera: naturwiss Ver Stmk 97, 76e80. Coniopterygidae). Fla. Entomol. 50, 285e293. Goossen, H., 1949. Untersuchungen an Gehirnen verschieden grosser, jeweils ver- Nelson, D.R., Freeman, T.P., Buckner, J.S., 2000. Waxes and lipids associated with the wandter Coleopteren und Hymenopteren. Zool. Jahrb. Abt. Allgem. Zool. Phys- external waxy structures of nymphs and pupae of the giant whitefly, Aleur- iol. Tiere. 62, 1e64. odicus dugesii. Comp. Biochem. Physiol. B 125, 265e278. Grebennikov, V.V., Beutel, R.G., 2002. Morphology of the minute larva of Ptinella Nelson, D.R., Freeman, T.P., Buckner, J.S., Hoelmer, K.A., Jackson, C.G., Hagler, J.R., tenella, with special reference to effects on miniaturisation and the systematic 2003. Characterization of the cuticular surface wax pores and the waxy 14 S. Randolf, D. Zimmermann / Arthropod Structure & Development 50 (2019) 1e14

particles of the dustywing, Semidalis flinti (Neuroptera: Coniopterygidae). Rensch, B., 1948. Histological changes correlated with evolutionary changes of body Comp. Biochem. Physiol. B 136, 343e356. size. Evolution 2 (3), 218e230. Neville, C., 1998. The significance of insect cuticle. In: Harrison, F.W., Locke, M. (Eds.), Retnakaran, A., Ennis, T., Jobin, L., Granett, J., 1979. Scanning electronmicroscopic Microscopic Anatomy of Invertebrates, 11A. Wiley-Liss, New York, pp. 151e176. study of wax distribution on the balsam woolly aphid, Adelges piceae (Homo- New, T.R., 1989. Planipennia, Lacewings. Handbuch der Zoologie, vol. 4 (Arthropoda: ptera, Adelgidae). Can. Entomol. 111, 67e72. Insecta), Part 30. Walter de Gruyter, Berlin. Riek, E.F., 1975. On the phylogenetic position of Brucheiser argentinus Navas 1927 Niven, J.E., Farris, S.M., 2012. Miniaturization of nervous systems and neurons. Curr. and description of a second species from Chile (Insecta: Neuroptera). Stud. Biol. 22 (9), R323eR329. Neotrop. Fauna 10, 117e126. Ohm, P., 1968. Vorlau€ fige Beschreibung einer neuen europaischen€ Aleuropteryx-Art Rousset, A., 1966. Morphologie cephalique des larves de Planipennes (Insectes (Neuroptera, Coniopterygidae). Ent. Nachrbl. Wien 15, 12e15. Nevropt eroïdes). Mem. Mus. Hist. Nat. Ser. A Zool. 42, 1e199. Partmann, W., 1948. Untersuchungen über die komplexe Auswirkung phylogene- Schmidt-Nielsen, K., 1984. Scaling: Why is animal size so important? Cambridge tischer Korpergr€ oßen€ anderungen€ bei Dipteren. Zool. Jahrb. Abt. Anat. Ontog. University Press, Cambridge. Tiere 69, 507e558. Schneeberg, K., Polilov, A.A., Harris, M.O., Beutel, R.G., 2013. The adult head Pass, G., 1980. The anatomy and ultrastructure of the antennal circulatory organs in morphology of the hessian fly Mayetiola destructor (Diptera, Cecidomyiidae). the cockhafer beetle Melolontha melolontha L. (Coleoptera, Scarabaeidae). J. Morphol. 274 (10), 1299e1311. Zoomorphology 96, 77e89. Shepard, F.D., 1967. The Head Capsule and Cervix of Adult Neuroptera (Insecta). A Polilov, A.A., 2005. Anatomy of the feather-winged beetles Acrotrichis montandoni Comparative Morphological Study. PhD Thesis. Harvard University. and Ptilium myrmecophilum (Coleoptera, Ptiliidae). Zool. Zh. 84 (2), 181e189 Smith, R.G., 1999. Wax glands, wax production and the functional significance of wax [Entomol Rev 85(5), 467e475]. use in three aphid species (Homoptera: Aphididae). J. Nat. Hist. 33, 513e530. Polilov, A.A., 2008. Anatomy of the smallest Coleoptera, featherwing beetles of the Snodgrass, R.E., 1935. Principles of Insect Morphology. MaGraw-Hill, New York. tribe Nanosellini (Coleoptera, Ptiliidae), and limits of insect miniaturization. Snodgrass, R.E., 1960. Facts and Theories Concerning the Insect Head. Smithsonian Zool. Zh. 87 (2), 181e188 [Entomol Rev 88(1), 26e33]. Institution, Wahington, DC. Polilov, A.A., 2011. Thoracic musculature of Sericoderus lateralis (Coleoptera, Cor- Sulc, K., 1914. Über die Stinkdrüsen und Speicheldrüsen der Chrysopen. Sitzungsber ylophidae): miniaturization effects and flight muscle degeneration related to bohm€ Ges Wiss Prag 11, 1e50. development of reproductive system. Zool. Zh. 90 (6), 698e705 [Entomol Rev Sundermeier, W., 1940. Der Hautpanzer des Kopfes und des Thorax von Myrmeleon 91(6), 735e742]. europaeus und seine Metamorphose. Zool. Jahrb. Abt. Anat. Ontog. Tiere 66, 291e348. Polilov, A.A., 2012. The smallest insects evolve anucleate neurons. Arthropod Struct. Sziraki, G., 2011. Coniopterygidae of the World: Annotated Check-List and Identi- Dev. 41, 27e32. fication Keys for Living Species, Species Groups and Supraspecific Taxa of the Polilov, A.A., 2015a. Small is beautiful: features of the smallest insects and limits to Family. Lap Lambert Academic Publishing, Saarbrücken, Germany. miniaturization. Annu. Rev. Entomol. 60, 103e121. https://doi.org/10.1146/ Tillyard, R.J., 1926. The Insects of Australia and New Zealand. Angus and Robertson, annurev-ento-010814-020924. Sydney. Polilov, A.A., 2015b. Consequences of miniaturization in insect morphology. Mos- Tjeder, B., 1957. Neuroptera e Planipennia. The lace-wings of Southern Africa. 1. cow Univ. Biol. Sci. Bull. 70 (3), 136e142. Introduction and families Coniopterygidae, Sisyridae, and osmylidae. In: Polilov, A.A., 2016a. Features of the structure of Hymenoptera associated with Hanstrom,€ B., Brinck, P., Rudebec, G. (Eds.), South African Animal Life, vol. 4. miniaturization: 1. Anatomy of the fairyfly Anaphes flavipes (Hymenoptera, Swedish Natural Science Research Council, Stockholm, pp. 95e188. Mymaridae). Zool. Zh. 95 (5), 567e578 [Entomol Rev 96(4), 407e418]. Tjeder, B.,1959. Neuroptera e Planipennia. The lace-wings of Southern Africa. 2. Family Polilov, A.A., 2016b. Features of the structure of Hymenoptera associated with Berothidae. In: Hanstrom,€ B., Brinck, P., Rudebec, G. (Eds.), South African Animal miniaturization: 2. Anatomy of the Trichogramma evanescens (Hymenoptera, Life, vol. 6. Swedish Natural Science Research Council, Stockholm, pp. 256e314. Trichogrammatidae). Zool. Zh. 95 (6), 699e711 [Entomol Rev 96(4), 419e31]. Tjeder, B.,1960. Neuroptera e Planipennia. The lace-wings of Southern Africa. 3. Family Polilov, A.A., 2016c. At the Size Limit - Effects of Miniaturization in Insects. Springer Psychopsidae. In: Hanstrom,€ B., Brinck, P., Rudebec, G. (Eds.), South African Animal Int Publ, Cham. Life, vol. 7. Swedish Natural Science Research Council, Stockholm, pp. 164e209. Polilov, A.A., Beutel, R.G., 2009. Miniaturization effects in larvae and adults of Mi- Wipfler, B., Machida, R., Müller, B., Beutel, R.G., 2011. On the head morphology of kado sp. (Coleoptera: Ptiliidae), one of the smallest free-living insects. Grylloblattodea (Insecta) and the systematic position of the order, with a new Arthropod Struct. Dev. 38, 247e270. nomenclature for the head muscles of Dicondylia. Syst. Entomol. 36, 241e266. Polilov, A.A., Beutel, R.G., 2010. Developmental stages of the hooded beetle Ser- Wipfler, B., Pass, G., 2014. Antennal heart morphology supports relationship of icoderus lateralis (Coleoptera: Corylophidae) with comments on the phyloge- Zoraptera with polyneopteran insects. Syst. Entomol. 39, 800e805. netic position and effects of miniaturization. Arthropod Struct. Dev. 39, Withycombe, C.L., 1925. Some aspects of the biology and morphology of the Neu- 52e69. roptera. With special reference to the immature stages and their possible Polilov, A.A., Makarova, A.A., 2017. The scaling and allometry of organ size associ- phylogenetic significance. Trans. Ethnol. Soc. Lond. 72, 303e411. ated with miniaturization in insects: a case study for Coleoptera and Hyme- Yavorskaya, M.I., Anton, E., Jałoszynski, P., Polilov, A., Beutel, R.G., 2018. Cephalic noptera. Sci. Rep. 7, 43095. anatomy of Sphaeriusidae and a morphology-based phylogeny of the suborder Polilov, A.A., Shmakov, A.S., 2016. The anatomy of the thrips Heliothrips haemor- Myxophaga (Coleoptera). Syst. Entomol. 43, 777e797. rhoidalis (Thysanoptera, Thripidae) and its specific features caused by minia- Yavorskaya, M.I., Polilov, A.A., 2016. Morphology of the head of Sericoderus lateralis turization. Arthropod Struct. Dev. 45, 496e507. (Coleoptera, Corylophidae) with comments on the effects of Miniaturization. Pope, R.D., 1983. Some aphid waxes, their form and function (Homoptera: Aphi- Zool. Zh. 95 (5), 545e556 [Entomol Rev 96(4), 395e406]. didae). J. Nat. Hist. 17 (4), 489e506. Yuasa, H., 1920. The anatomy of the head and mouth-parts of Orthoptera and Pradhan, S., 1939. Glands in the head capsule of coccinellid beetles with a discus- Euplexoptera. J. Morphol. 33, 251e307. sion on some aspects of gnathal glands. J. Morphol. 64, 47e66. Zimmermann, D., Klepal, W., Aspock,€ U., 2009. The first SEM study on Randolf, S., Zimmermann, D., Aspock,€ U., 2013. Head anatomy of adult Sisyra ter- Coniopterygidae (Neuroptera) e structural evidence and phylogenetic impli- minalis (Insecta: Neuroptera: Sisyridae) e functional adaptations and phylo- cations. Eur. J. Entomol. 106, 651e662. genetic implications. Arthropod Struct. Dev. 42, 565e582. Zimmermann, D., Randolf, S., Metscher, B.D., Aspock,€ U., 2011. The function and Randolf, S., Zimmermann, D., Aspock,€ U., 2014. Head anatomy of adult Nevrorthus phylogenetic implications of the tentorium in adult Neuroptera (Insecta). apatelios and basal splitting events in Neuroptera (Neuroptera: Nevrorthidae). Arthropod Struct. Dev. 40, 571e582. Arthropod Syst. Phylogeny 72 (2), 111e136. Zimmermann, D., Vilhelmsen, V., 2016. The sister group of Aculeata (Hymenoptera) Randolf, S., Zimmermann, D., Aspock,€ U., 2017. Head anatomy of adult Coniopteryx e evidence from internal head anatomy, with emphasis on the tentorium. pygmaea Enderlein, 1906: effects of miniaturization and the systematic position Arthropod Syst. Phylo. 74, 195e218. of Coniopterygidae (Insecta: Neuroptera). Arthropod Struct. Dev. 46, 304e322.