Opamyrma hungvuong YAMANE, BUI & EGUCHI, 2 008, 2008

Yamada, Aiki, Nguyen, Dai D. & Eguchi, Katsuyuki, 2020, Unveiling the morphology of the Oriental rare monotypic ant genus Opamyrma YAMANE, BUI & EGUCHI, 2008 (Hymenoptera: Formicidae: Leptanillinae) and its evolutionary implications, with first descriptions of the male, larva, tentorium, and sting apparatus, Myrmecological News 30, pp. 27-52 : 30-47

Opamyrma hungvuong YAMANE, BUI & EGUCHI, 2 008

( Figs. 1 - 1 5 )

Non-type material examined: China: 25 workers, 6 larvae (colony ID: AKY 05vii17-06), Guangxi, Guilin, Huaping National Nature Reserve , 25.57° N, 109.94° E, ca. 1000 - 1500 m above sea level (a.s.l.), collected from soil under stone on forest floor, coll. A. Yamada, 5 July 2017 ( AKYC, ACEG, GXNU, MCZC, MHNG) . Vietnam: 3 workers, 2 alate queens, 5 dealate queens, 2 males (colony ID: Dai19iii2019-029 ), Son La, Ta Xua Nature Reserve, Bac Yen, Hang Dong , 21.3158° N, 104.5213° E, 1533 m a.s.l., collected from soil on forest floor, coll. D. D. Nguyen, 14 March 2019 ( AKYC, ACEG, IEBR, MCZC, MHNG) .

Diagnosis: The female (worker and queen) of the unique species is easily recognizable by the following

combination of characteristics: 1) occipital carina virtually uninterrupted and anteriorly located before the posterior margin of cranium; 2) outer face of labrum bears numerous peg-like setae; 3) waist 1-segmented; 4) petiole without distinct anterior peduncle; 5) tergosternal fusion of petiole present only anteriorly; 6) gaster elongated and flattened laterally, with distinct presclerites in abdominal segment IV. The male may be recognizable by the following combination of characteristics: 1) mandible reduced and nub-like; 2) wing venation reduced (Ogata’s venation type IVb) with only three closed cells, that is, basal, subbasal, and discal cells; 3) propodeal lobes inconspicuous; 4) waist 1-segmented; 5) petiole not tergosternally fused; 6) pygostyli absent; 7) abdominal sternite IX without prongs or teeth, and with posteromedian lobe; 8) genitalia conspicuous with extremely elongate telomere directed ventrad in repose.

Measurements and indices: Worker: CI 76 - 82; HL 0.62 - 0.71 mm; HW 0.48 - 0.54 mm; MFI 91 - 96; MFL 0.44 - 0.50 mm; PTH 0.28 - 0.38 mm; PTI 46 - 50; PTL 0.42 - 0.55 mm; PTW 0.21 - 0.27 mm; PW 0.35 - 0.43 mm; SI 64 - 71; SL 0.33 - 0.38 mm; WL 1.01 - 1.18mm (n = 7).

Queen: CI 78 - 79; EI 24 - 25; EL 0.17 mm; HL 0.86 - 0.87 mm; HW 0.68 mm; MFI 89 - 92; MFL 0.61 - 0.63 mm; OI 8 - 9; OL 0.05 - 0.06 mm; PTH 0.48 - 0.49 mm; PTI 50 - 56; PTL 0.69 - 0.70 mm; PTW 0.35 - 0.38 mm; PW 0.58 - 0.60 mm; SI 67 - 69; SL 0.45 - 0.47 mm; WL 1.58 - 1.63 mm (n = 3).

Male: CI 99 - 106; EI 53 - 56; EL 0.33 mm; HL 0.59 mm; HW 0.58 - 0.62 mm; MFI 104 - 109; MFL 0.64 - 0.65 mm; OI 15; OL 0.09 - 0.10mm; PTH 0.36 - 0.37 mm; PTI 92 - 99; PTL 0.34 - 0.36 mm; PTW 0.31 - 0.35 mm; PW 0.53 mm; SI 19; SL 0.11 - 0.12 mm; WL 1.48 - 1.49 mm (n = 2).

Redescription: Worker ( Figs. 1 - 9 ): C r a n i u m. In full-face view subrectangular, longer than wide, with slightly convex lateral margin and slightly concave posterior margin, in lateral view, flattened dorsoventrally. Median longitudinal cephalic carina absent. Frontal carina and lobes absent. Occiput extended anteriorly to have distinct dorsal, lateral, and ventral face, delimited anteriorly by distinct occipital carina (“Occ” in Figs. 1A - B , 2B , 4C ; = “preoccipital carina” in the original description); the carina virtually uninterrupted, forming a V-shaped angle at the middle of the venter (arrow in Fig.2B ). Postgenal ridge (“Pgr” in Figs. 1B , 4C ) externally visible as a dark line running on the ventral midline, ending a little before the level of occipital carina (the dark line was mentioned as “median furrow” in the original description, but the ventral midline is not furrowed as seen in Fig. 2B ). Hypostomal process (“Hysp” in Fig. 2B, D ) conspicuous, in lateral view broad with rounded apex. Eye and ocelli completely absent. Antennal socket completely exposed in full-face view, directing almost dorsad, located in a large, roundly excavated area of which anterior wall is steep a little behind the anterior margin of clypeus; the area not clearly defined posteriorly. Antennal torulus distinct, simple annular, located distant from anterior clypeal margin, posterolaterally surrounded by deep tear- drop-shaped peritorular groove (“Ptg” in Figs. 2A , 4A - B ; the term “peritorular groove” is borrowed from RICHTER & al. 2019). Anterior tentorial pit not externally visible (see tentorium description below). Posterior tentorial pit (“Ptp” in Figs.2B , 4C ) located laterally to postocciput. Median portion of clypeus rather clearly divided into anterior steep slope and posterior horizontal area that is raised dorsad and posteriorly roundly delimited by a continuous steep declivity; posterior area broadly inserted between antennal sockets, nearly reaching the level of posterior margin of antennal torulus; supraclypeal area (“Sca” in Fig.2A ) small, subtriangular; median longitudinal clypeal carina absent; lateral portion of clypeus in front of antennal socket very narrow anteroposteriorly: posterior limit of lateral portion of clypeus externally not obvious, but internal line that might be paroculoclypeal sulcus (dashed line in Fig.4A ) tracing the anterior outline of excavated area around antennal socket is recognized under transmitted light microscope; anterior clypeal margin broadly concave without any peg-like setae or cuticular denticles.

M o u t h p a r t s. Mandible short and sublinear, strongly curved near the distal end of mandalus, with long but somewhat bluntly tapering apical tooth followed by a broad trapezoidal preapical tooth (“Pat” in Fig. 2C, E ; in the original description, the preapical tooth was mentioned as “trapezoidal lobe” that was interpreted as fusion of two preapical teeth, but it could well be a single preapical tooth corresponding in location to, for example, Apomyrma , † Gerontoformica NEL & PERRAULT, 2004, and Prionopelta MAYR, 1866) and three or four inconspicuous teeth; ventral face with a single peg-like seta (“Mps” in Fig. 2A, C, E ; the seta morphology is similar to that of labrum) which is located near the base of the second and third inconspicuous teeth of the masticatory margin, and two long apically spatulate setae (arrows in Fig. 2C, E ); trulleum apparently absent; canthellus (“Ctl” in Fig.2C, E ) less-defined, not differentiated from the basal margin of mandible; mandalus (“Mdl” marked by red color in Fig.2C ) elongate and narrow club-shaped (it is visible as whitish membranous area in dry specimen under an optical microscope, and it was misinterpreted as trulleum in the original description). Labrum ( Fig. 2F , “Lbr” in Fig. 1B ) large, entirely concealing prementum (“Prm” in Fig. 3A, C ) and maxillary stipes (“Mxst” in Fig. 3A - B ) when mouthparts retracted, almost as long as wide, with rounded distal margin (median cleft absent); labral tuberculi absent; basal third of the outer face bearing numerous peg-like setae that are arranged regularly but not in strict transverse rows (“Lps” in Fig. 2A, F ); distal area of the outer face with at least five pairs of long apically spatulate setae (halves of the pairs are indicated by arrows in Fig. 2F ) that are regularly arranged. Maxilla with conspicuous maxillary comb (“Mxco” in Fig.3B ); transverse stipital groove absent; galeal comb absent; galeal crown flattened with a series of thick apically rounded (not spatulate) setae, one of which is particularly stout (“Gcss” in Fig.3A - B ), without ventral comb; lacinia (“Lcn” in Fig.3B ) small subtriangular, with relatively acute apex; lacinial comb present, composed of short thin setae; maxillary palp (“Mxp” in Fig.3A - B ) 4-segmented, becoming shorter and narrower apically; apical segment with bluntly tapering apex. Premental shield (ventral surface of prementum, marked by red color in Fig. 3A ) convex oblong in ventral view, without transverse premental groove. Labium in dorsal view with conspicuous anteromedian sclerite (“Ams” in Fig. 3D ) that is apparently dorsal extension of prementum; base of subglossal brush (“Sglb” in Fig.3C - D ) forming strong anterolateral projection in dorsal view (arrow in Fig. 3D ); paraglossa unrecognizable in our observation; labial palp (“Lbp” in Fig. 3A, C - D ) 2-segmented; second segment about as long as first segment, with rounded apex.

T e n t o r i u m. Anterior tentorial arm (“Ata” in Fig.4B - D ) originated from endoskeletal structure of antennal socket; anterior tentorial pit apparently located on medioventral wall of antennal socket (“Atp” in Fig. 4A - B ). Buttress-like extension absent. Internal plate (“Ip” in Fig.4B, D ) relatively narrow but much broader than external plate (“Ep” in Fig.4D ), with rounded anterodistal corner. Dorsal tentorial arm (“Dta” in Fig.4D ) distinct, with long branchlike apical part. Tentorial bridge (“Tb” in Fig.4C - D ) thin tubular. Corpotendon (“Ct” in Fig.4C - D ) long. Posterior tentorial arm (“Pta” in Fig.4C ) thin tubular.

A n t e n n a. Antenna 12-merous, gradually incrassate from antennomeres II to XII ( Fig. 5A ). Antennal scape, when laid backward, extending past midlength of cranium, flattened dorsoventrally, narrowed toward base, without distinct basal flange distal to bulbus; antennomere II subconical bead-like, in dorsal view strongly narrowed at base, slightly longer than wide; antennomore III slightly longer than wide and narrowed basally; antennomeres IV and V almost as long as wide; antennomeres VI - XI wider than long; apical antennomere longer than wide and bluntly pointed at apex. Apical antennomere, with at least two types of sensilla recognizable: basiconic (black arrows in Fig.5B ), and trichodic ones; trichodic sensilla become small on basal marginal area; pit-like structures that might be coeloconic / ampullaceous sensilla or socket of broken basiconic / trichodic sensilla also recognizable (white arrows in Fig.5B ). Scape bulbus hemispherical with short tubular neck; anterior basal margin of the bulbus apparently without a distinct notch.

M e s o s o m a. Mesosoma slender and consisting of two distinct portions, prothorax and meso-metathoracico-propodeal complex, which is oblong and slightly longer and narrower than pronotum and almost parallel-sided in dorsal view: articulation between prothorax and mesothorax unfused and fully flexible in fresh condition. Pronotum longer than wide in dorsal view, with slightly convex dorsal face that roundly continues to lateral face; anterior slope short and steep. Propleurae unfused relative to one another, but are strongly attached along the ventral midline. Procoxal cavity (“Pcc” in Fig. 6D, F ) as small as meso- and metacoxal cavities, in ventral view bounded anteriorly by propleuron and laterally and posteriorly by prosternum (virtually not bounded by pronotum). Dorsum of anterior articulatory area of mesonotum (inserted under the pronotum, marked by blue color in Fig.6B - C ) posteriorly delimited by deep narrow transverse groove (“Msg”, marked by red color in Fig.6B - C ) which continues along the ventral margin of mesopleuron. Mesonotal spiracle unrecognizable in our observation. Notopleural suture of mesothorax absent. Longitudinal mesopleural sulcus absent. Metanotal groove absent. Mesometapleural suture present as weak groove. Metanotal spiracle (“Mtsp” in Fig.6A ) small and apparently closed, located high on lateral face. Propodeum with rather flat dorsum and steep posterior face; posterior face roundly continues to dorsal and lateral faces without any delimiting carina. Propodeal spiracle located relatively low on the lateral face of propodeum. Outline of metapleural gland bulla conspicuously recognized through cuticle under natural lighting, subcircular, occupying posterior two-fifths of ventrolateral part of the pleuron; metapleural gland orifice (“Mgo” in Fig. 6E ) narrow slit-like, located in the lower posterior corner of the metapleuron; metapleural longitudinal flange (“Mlf”, marked by green color in Fig.6E ) anter- oposteriorly long, projecting laterad and overhanging (but not concealing) metapleural gland orifice. Ventral part of metapleuron below the orifice also laterally produced to form longitudinal flange. Propodeal lobes (“Pdl” in Fig. 6C - E ) weakly present, low and round. Anteroventral face of mesopectus with distinct median carina and submedial deep subrectangular depressions that accommodate the forecoxae; posterior remaining face just medially weakly raised without forming distinct median carina. Mesosternal pit present (“Mstp” in Fig. 6D ). Metasternal pit apparently absent. Meso- and metacoxal cavities small, fully closed with a complete cuticular annuli surrounding the cavities; metacoxal cavity separated from propodeal foramen by a cuticular band.

L e g s. Relatively broad gap present between pro- and mesocoxae. Metacoxal dorsum unarmed. Profemur broader than meso- and metafemur. Protibia broader than meso- and metatibia. Anterior face of protibia without “protibial anterior sulcus” sensu KELLER (2011). The calcar of the strigil (“Ca” in Fig. 7A - C ) fully pectinated; basal one third of the calcar bearing narrow unnotched lamina (arrow in Fig.7B ); anterior surface with brush that is composed of dense seta-like cuticular projections; posterior surface with sparse seta-like cuticular projections. Pos- terodistal apex of protibia with a single stout seta (“Ptss” in Fig.7C ), located close to the insertion of the calcar of the strigil. Meso- and meta- tibiae each with a reduced barbu- late anterior spur (“Ats” in Fig.7E, H ) and a well-developed pectinate posterior spur (“Pts” in Fig. E - F, H); posterior spurs with dense seta-like cuticular projections except for basiposterior surface of the metatibial spur. Apically truncated and somewhat flattened setae present on poste- rior face of metatibia near insertion of the posterior spur; similar setae also present posterior face of metabasitarsus along its inner margin (arrows in Fig.7F ). Anterior surface of probasitarsal notch with numerous acute scale-like cuticular projections ( Fig. 7A - B ); posterior surface of the probasitarsal notch without any stout spiniform seta ( Fig.7C ). Anterior surfaces of distal portion of protibia and probasitarsus bearing numerous spatulate setae ( Fig. 7A - B ). Basiventral margin of probasitarsus just rounded, not strongly produced. Posteroventral corner of protarsomeres I - III respectively with some conspicuous stout spiniform setae (arrows in Fig. 7D ). Stout spiniform setae absent on mesotibia, mesobasitarsus, and metabasitarsus (except for stout setae near distal margin of mesobasitarsus). Pretarsal manubrium (“Mnb” in Fig.7G ) relatively large, flat and longitudinal elliptical, with a pair of stout long setae (no significant differences between those of pro-, meso- and meta legs). Pretarsal claws simple, without teeth ( Fig.7G ).

M e t a s o m a. Waist 1-segmented, that is, consisting of only petiole (abdominal segment II). Petiole subrectangular to oblong in lateral view, virtually sessile without distinct anterior peduncle, longer than wide in dorsal view, with slightly convex dorsal face that roundly continues to lateral face; petiolar sternite in ventral view (“Ptsn”, marked by blue color in Fig.8B ) disproportionate dumbbell-shaped, with narrow elongated anterior part, only anteriorly fused with the tergite; posterior part of the sternite delimited from the tergite by distinct tergosternal suture (“Tss” in Fig.8B ); petiolar laterotergite (“Ptlt”, marked by green color in Fig.8B ) present as narrow area along the tergosternal suture; petiolar spiracle located anteriorly on the lateral face of the tergite at its midheight; anteroventral corner of petiole with flange-like structure (arrow in Fig.8A - B ); petiolar levator process complete, without lacuna; very short tubular posterior peduncle present inside which the helcium articulates. Gaster very elongate and laterally compressed especially in posterior segments, in lateral view highest at the posterior end of abdominal segment V. Helcium axial (sensu KELLER 2011), tergosternally fused; helcium sternite laterally enclosed in the tergite. Postsclerites of abdominal segment III tergosternally unfused, having a free anterior face above the helcium, longer than high, narrowed basally in dorsal view, longer than segments IV, V and VI. Prora of abdominal sternite III present as a strong corner that is produced anteriad to reaching the level of the anteriormost point of tergite III. Abdominal spiracle III located on lower lateral face of the tergite. Abdominal segment IV with externally visible presclerites; pretergite (“Prtg-IV” in Fig. 8E - F ) short and inconspicuous, just weakly constricted; presternite (“Prsn-IV” in Fig.8F - G ) long and conspicuous, posteriorly delimited by strong constriction. Abdominal spiracles IV - V visible, but VI - VII concealed by preceding tergites (the original description stated that spiracles V is concealed, but it is clearly visible as indicated by arrow in Fig.8F ). Abdominal segment VII longest among the segments III - VII. Pygidium (abdominal tergite VII) very large and simple, unarmed, convex and downcurved posteriorly in lateral view. Hypopygium (abdominal sternite VII) unarmed, in ventral view long subtriangular.

S t i n g a p p a r a t u s. Lateral hemitergites of spiracular plate (abdominal tergite VIII) narrowly attached each other by large medial connection (“Mc” in Fig. 9A ); the attachment present as a suture-like, strongly sclerotized midline; median connection distinctly delimited from the main disc (= “body” sensu KUGLER, 1978) by a weak carina (indicated by dashed line in Fig. 9A ); main disc subrectangular with broadly concave posterodorsal margin, without distinct dorsal notch; spiracle (arrow in Fig. 9A ) relatively large, located lower (ventrad) center of the disc; posteroventral corner without posterodorsal lobe and tubercle; anterior apodeme (“Ap” in Fig.9A ) narrow. Anterior apodeme (“Ap” in Fig. 9B ) of quadrate plate (abdominal tergite IX) much smaller than its main disc, delimited by distinct midplate line (partially indicated by dashed line in Fig. 9B ), with large lateral lobe (“Ll” in Fig. 9B ); anterodorsal corner (arrow in Fig.9B ) long and sharp. Anal arcs and plate present (“Ana” and “Anp” in Fig. 9C ), weakly sclerotized apparently without anal sensilla. Anterior apodeme (“Ap” in Fig. 9D ) of oblong plate (gonocoxa IX; = second valvifer) forming small subtriangular sclerite in lateral view, that is posteriorly margined by diverging thickened ridge that is connected with dorsal ridge of the posterior arm (“Pa” in Fig. 9D ); posterior arm relatively large, more than twice as long as high in lateral view: dorsal subterminal part of the arm (arrow in Fig.9D ) forming weakly sclerotized flange protruding from the dorsal ridge; most of ventral arm inconspicuous and apparently membranous; fulcral arm (“Fa” in Fig.9L ) large and linear. Basal part of triangular plate (gonangulum; = first valvifer; “Tp” in Fig. 9D ) long and thin, weakly curved; lateral tubercle apparently absent; dorsoapical and ventroapical processes short and stout. Gonostylus (gonoplac; = third valvula; “Gs” in Fig.9D, E ) long and slender, composed of 2 distinct segments; first segment long and feebly sclerotized except for well-sclerotized dorsal margin, with sparse short erect setae along dorsal margin and on posterior part of its outer face; second segment short, relatively well-sclerotized, with denser and longer erect setae on its outer face. Furcula ( Fig.9F - G ) thick, Y-shaped in posterior view, with short dorsal arm, unfused with sting base. Sting (gonapophysis IX; = stylet, second valvula; Fig. 9H - K ) very narrow elongate and blade-like; sting bulb conspicuously wider and higher than base of the shaft; valve chamber (“Vc” in Fig.9J ) present but narrow; sting shaft more than twice as long as valve chamber, upcurved, with two pairs of small barbs on the apex (arrows at “St” in Fig.9K ); distiventral edge of the shaft produced to form broad lamina (arrow in Fig. 9H ). Lancet (gonapophysis VIII; = first valvula; “Lc” in Fig.9L ) completely lacks valves, with 5 apical barbs of which basal three are conspicuously large and directed ventrad, and apical two are small and inconspicuous.

C o l o r, s c u l p t u r e, a n d p i l o s i t y. Body entirely light orangish brown, with slightly yellowish antennae and legs. Body largely smooth and shining. Body largely covered with sparse to dense decumbent / standing hairs as shown in figures: hairs most dense in dorsum of cranium, and most sparse in posterolateral face of mesonotum and lateral face of petiole; a series of particularly thicker and longer hairs present along anterior margin of cranium in full-face view.

QUeeN ( FIG.1 0): Fully winged, largely similar to the worker except for optic- and flight-related characters de- scribed below. Eyes and ocelli large and conspicuous; eyes circular with about 15 ommatidia at maximum diameter in lateral view, located a little lower of mid-length of cranium in full-face view; ocelli located high close to occipital carina. Occipital carina (“Occ” in Fig. 1 0C) nearly complete, but interrupted at midline of the venter. Postgenal ridge (“Pgr” in Fig.1 0C) extending more posteriorly, beyond the ventral interruption of occipital carina. Mesosoma having full complement of flight sclerites but still slender, with almost linear dorsal outline in lateral view; mesonotum not raised dorsally. Pronotum having large dorsal face as that of the worker. Dorsum of anterior articulatory area of mesonotum that inserted under the pronotum (marked by blue color in Fig. 1 0E - F) posteriorly delimited by a faint line and submedial weak narrow transverse grooves (“Msg”, marked by red color in Fig. 1 0E - F) that is possibly homologous with that of the worker. Mesoscutum in dorsal view oval, much wider than long (excluding the anterior articulatory area); notauli absent; parapsidal lines (“Pl” in Fig. 1 0F) faintly present. Parascutal carinae weak. Preaxilla (“Prx”, marked by yellow color in Fig. 1 0E - F) distinctly visible as narrow area in dorsal view. Axillae (“Axa”, marked by purple color in Fig. 1 0E - F) in dorsal view large, strongly extending medially between mesoscutum and mesoscutellum but not meeting at midline. Axillulae (“Axu”, marked by green color in Fig. 1 0E - F) large and conspicuous in dorsal view, virtually meeting each other behind mesoscutellum. Scutoscutellar sulcus (“Scs” in Fig.1 0F) weak, very narrow and only faintly scrobiculate. Mesoscutellum in dorsal view circular, a little wider than long. Metascutellum large and conspicuous in dorsal view, not strongly produced in lateral view. Wing venation largely same as that of male ( Fig.1 0G - H, see also male description below), but Rsf2 faintly recognized as a vestigial spectral line in the queen forewing. Sting apparatus largely same as that of the worker.

Male ( Figs. 1 1 - 13): C r a n i u m. In full-face view circular, almost as long as wide excluding eyes, with strongly convex posterior margin. Frontal carinae and lobes absent. Occipital carina absent. Eye and ocelli large and conspicuous; ocelli distantly located from eyes: median ocellus located just posterior to two-thirds of posterior part of cranium above eyes in full-face view. Antennal socket located in a large, roundly excavated area of which anterior wall is steep just behind the posterior margin of clypeus; the area not clearly defined posteriorly. Antennal torulus distinct, simple annular, distantly located from posterior clypeal margin (the distance slightly less than one torulus diameter). Anterior tentorial pit (“Atp” in Fig. 1 1A ) situated anterior to antennal torulus. Median portion of the clypeus roundly raised dorsad; posterior area not inserted between antennal toruli, not quite reaching the level of anterior margin of the torulus; supraclypeal area distinct but indistinctly margined; lateral portion of clypeus in front of antennal socket narrow anteroposteriorly; median anterior clypeal margin weakly broadly concave, without any peg-like dentiform setae. Antenna 13-merous, filiform without becoming incrassate apically. Antennal scape short cylindrical, when laid backward, not reaching the level of posterior margin of eye in full-face view; antennomere II bead-like and shortest among antennomeres; antennomeres III–XII longer than wide, almost same length; antennomere XIII longest, with bluntly tapering apex. Mandibles strongly reduced, subtriangular nub-like, forming a broad gap when fully closed ( Fig. 1 1A, C ); masticatory margin edentate; mandalus (“Mdl” in Fig.1 1A, C ) large but still ringed by sclerite in dorsal view. Labrum (“Lbr” in Fig. 1 1C ) subrectangular, more than twice as wide as long, with almost straight distal margin (median cleft absent); labral tuberculi absent; peg-like dentiform setae absent. Maxillary palp (“Mxp” in Fig.1 1C ) 4-segmented. Labial palp (“Lbp” in Fig.1 1C ) 2-segmented.

M e s o s o m a. Pronotum with conspicuously narrowed cervical shield; median pronotal area behind cervical shield convex and short in lateral view; maximum height of pronotum almost as long as mesoscutum height in lateral view. Mesoscutum large in dorsal view, much longer than wide; lateral margin concave around the anterior terminus of notauli. Notauli (“Nt” in Fig. 1 1D ) distinct and weakly scrobiculate, meeting each other at the midline, but not extending to transscutal line (the posterior terminus located far from the transscutal line). Parapsidal line (“Pl”, indicated by dashed line in Fig. 1 1D ) present, weakly undulate. Parascutal carinae weak. Preaxilla distinctly visible as small area in dorsal view (“Prx” in Fig.1 1D ). Axillae small and conspicuous in dorsal view, moderately inserted between mesoscutum and mesoscutellum, not meeting each other at midline. Axillulae large and conspicuous in dorsal view, virtually meeting each other behind mesoscutellum. Scutoscutellar sulcus present as narrow and faintly scrobiculate groove, without crossribbing. Mesoscutellum in lateral view as high as mesoscutum, with convex dorsal margin, in dorsal view rounded subtrapezoidal, almost as long as wide. Metascutellum broad and conspicuously visible in dorsal view, in lateral view strongly produced. Mesopectus with oblique and weakly sinuate sulcus; anterior terminus of the sulcus located well ventral to pronotal corner. Metapleural spiracular plate absent. Anterior metapleural area weakly separated from posterior metapleural area by an inconspicuous transverse sulcus, and from propodeum by a deep conspicuous groove. Metapleural gland orifice occluded; internal structure of metapleural gland unrecognizable through metapleural sclerite. Propodeum in lateral view with roundly convex dorsal margin; posterior face roundly meeting dorsal and lateral faces without any delimiting carina; propodeal spiracle circular, large, low on lateral propodeal surface; propodeal lobe inconspicuous, just faintly developed. Metacoxal cavities fully closed with complete cuticular annuli surrounding the cavities, separated from propodeal foramen by a cuticular band.

M e t a s o m a. Waist 1-segmented, that is, consisting of only petiole (abdominal segment II). Petiole roundly swollen, virtually without distinct anterior peduncle, almost as long as wide and high, in lateral view with strongly convex dorsal margin; petiolar sternite unfused with the tergite, delimited by distinct tergosternal line (“Tsl” in Fig. 1 1E, G ) even in anterior articulatory area; the sternite broad in ventral view, in lateral view with weakly convex ventral margin; subpetiolar process absent; petiolar laterotergite absent. Helcium axial (sensu KELLER 2 011), with sternite visible in lateral view, not enclosed by pretergite. Abdominal postsclerites III tergosternally unfused. Prora of abdominal sternum III present just as weak carina delimiting poststernite from helcium; anteromedian area of helcium sternite concave. Abdominal tergites IV - VIII and abdominal sternites IV - IX well developed, not reduced or obscured. Abdominal segment IV without distinct presclerites. Abdominal spiracles III - V visible but VI - VIII concealed by preceding tergites. Abdominal segment IV longest among the segments III - VIII, a little longer than segments III and V. Abdominal tergite VIII unarmed.

W i n g s (F i g. 1 2). Wings hyaline, completely covered by fine setose layer. Forewing venation reduced with only three closed cells (basal, subbasal, and discal), categorized as Ogata’s venation type IVb, although discal cell enclosed by nebulous Rs + M and 1 m-cu; pterostigma large and conspicuous; free R distal to pterostigma absent; costal vein (C) tubular only in short basal part and soon disappearing distally (costal cell open); Rsf1 tubular, very short and nearly lost; Mf1 tubular, completely closing basal cell; Rs + M nebulous; Rsf2 absent; Rsf3 only partially weakly present as a short diverging branch from Rsf4 (submarginal cell 1 unclosed); Rsf4 + tubular, continuous with 2r-rs which is directed posteroapically, ending before wing apex (marginal cell 1 open); Mf3 + absent and 2rs-m absent (submarginal cell 2 absent); 1m-cu nebulous (discal cell 1 closed); M + Cu tubular (basal cell closed); Cuf2 - 3 nebulous; 1A tubular, disappearing distally after the connection with cu-a (subdiscal cell 1 open; subbasal cell closed). Hindwing venation reduced, only with tubular R + Rs and 1A, with six hamuli; R not reaching anterior wing margin; 1A short; claval region relatively developed, with rounded margin; jugal lobe absent.

G e n i t a l i a (F i g. 1 3). Genitalia large and extremely specialized; most part of telomere and apical part of penisvalvae visible in external lateral view, without distension or dissection (see Fig. 1 1F ). Pygostyles absent. Basal disc of abdominal sternite IX ( Fig.1 3C ) distinctly more than twice wider than long when excluding spiculum, with anterolateral corner just weakly produced; posterior lobe very narrow, about one sixth as wide as basal disc, distinctly longer than basal disc when excluding spiculum, with strongly convex posterior apex; spiculum (“Spc” in Fig. 1 3C ) long and acute, nearly as long as basal disc. Cupula ( Fig.1 3D , “Cu” in Fig.1 3B, E ) reduced, non-annular, only present as short half arc-shaped ventral sclerite. Parameres highly fused with each other both dorsally and ventrally (therefore a complete annulus formed), and also with penisvalvae dorsally, that is, parameres and pe- nisvalvae inseparable without destruction ( Fig. 1 3A - B ); basivolsellae also strongly fused with each other ventrally and with basimeres; basimere (“Bm” in Fig.1 3A - B, E, G ) well-developed, without oblique carina on lower face (“BmC” sensu YAMADA & EGUCHI 2016); telomere (“Tm” in Fig.1 3A, B, E ) extremely elongate, distinctly longer than basimere, weakly recurved anteroventrad, clearly visible in external lateral view (see Fig.1 1F ), gently tapering apicad; articulation of basimere to telomere apparently fused, but differentiated by ventral membranous notch. Cuspis (“Cs” in Fig.1 3A - B, E - F ) distinct, elongate digitiform, with several short-modified setae on apical face and normal standing hairs on basal face. Digitus (“Dg” in Fig. 1 3A - B, E - F ) club-shaped, with strongly swollen apical part directed laterad with numerous short modified setae on ventrolateral face. Penisvalvae ( Fig. 1 3G , “Pv” in Fig.1 3B ) not fused with each other directly, but connected to each other via apical extension of basimere (dorsal sclerite apparently seem not be part of penisvalvae, but apical extension of basimere that extends lateroventrad and is fused partly with lateral face of valviceps; see Fig. 1 3G ). Valvura (“Va” in Fig.1 3G ) elongate liner, directed anteroventrad. Valviceps with a modified lateral apodeme (“Lp” in Fig.1 3G ) that is visible as small semielliptic sclerite on mid-height of basal valviceps in lateral view. Valviceps also have a uniquely specialized structure termed here as “spinescent lobe” (“Spl” in Fig. 1 3A, G ); spinescent lobe originated from dorsoapical corner of the valviceps and extended ventrolaterally to form arc-shaped sclerite bearing numerous spines (therefore, it seems to be derived by extreme modification and sclerotization of penisvalvar membrane that commonly has numerous spines). Anteroventral corner of valviceps strongly produced with acute angle. Anterior part of ventral margin of valviceps with about 25 small teeth. Apical margin of valviceps rounded.

C o l o r, s c u l p t u r e, a n d p i l o s i t y. Body entirely black, with faintly paler antennae and legs; maxilla and labium whitish; telomere black; penisvalvae yellowish. Body largely smooth and shining. Body largely covered with sparse to dense decumbent / standing hairs as shown in figures; hairs most dense in dorsum of cranium, and sparser in mesosoma and metasoma.

Larva ( Figs. 1 4 - 15): Following description is based on relatively developed larvae whose instar is unknown (with head width around 0.11 mm). Body elongate and slender with proportionally small head. Cranium longitudinally oval in full-face view, with smooth and hairless surface; posteromedian part just behind the level of antennae strongly depressed. Antenna (“Atn” in Fig.1 4B - C ) consisting of three sensilla located at the anterior end of a sulcus which extends from posterior end of cranium (the “sulcus” well-recognized as internal ridge in Fig. 1 4B ). Mandible (“Mdb” in Fig.1 4B - E ) well-sclerotized, in dorsal view mostly concealed under labrum in the closed position, in dorsal view subtriangular with acute apex curved medially; masticatory margin linear and edentate. Maxilla with some cuticular spinules (black arrows in Fig.1 5A ); maxillary palp (“Mxp” in Fig.1 4C - E , Fig.1 5A ) stout with two basiconic sensilla (white arrows on “Mxp” in Fig.1 5A ); galea (“Gl” in Fig.1 4C - E ) slender and digitiform with two basiconic sensilla (white arrows on “Gl” in Fig.1 5A ) on the apex. Labrum (“Lbr” in Fig. 1 4B - E ) broad with anterior margin strongly and narrowly concave medially; surface near the anteroventral border with several basiconic sensilla (arrows in Fig. 1 5B ). Labium with dense cuticular spinules on anteroventral surface; anterior margin in ventral view weakly broadly concave medially; labial palp stout, with two basiconic sensilla (arrows in Fig. 1 5C ). Anteroventral surface of prothorax with dense transverse series of tiny cuticular spinules ( Figs. 1 4E , 15D). Body hairs unbranched, with two types: 1) short thin standing hairs that very densely cover abdominal segments and sparsely present in thoracic segments; 2) stout standing hairs that very sparsely present in thoracic and abdominal segments, and especially numerous in around abdominal terminus (see Fig.1 4F ). Specialized structures such as “prothoracic projection” and “hemolymph tap” known in the Leptanilla larva absent. Spiracles unrecognizable in our observation (probably tiny and inconspicuous, as in the genus Leptanilla ).

Distribution: This species has been recorded from southern area of China (Hainan, Guangxi) and northern central to northern Vietnam (Ha Tinh and Son La). Re- corded elevations ranges from ca. 640 m a.s.l (in Hainan) to ca. 1500 m a.s.l (in Son La); the elevation of the type locality was not recorded. The confirmed distributional records are mapped in Fig.1 6 .

BIoNoMICs: There are little data on the biology. Both of the two colonies examined in the present study were collected from soil on forest floor. The workers run agilely but didn’t climb up smooth plastic walls. All 12 of the larvae from colony AKY 05vii17-06 were approximately the same size, suggestive of brood cycles.

Figures

Fig.1: General habitus of Opamyrma hungvuong worker, nontype (AKY05vii17-06, China, Guangxi). (A) head in full-face view; (B) head in anteroventral view; (C) body in lateral view; (D) body in dorsal view. Abbreviations: Occ = occipital carina; Lbr = labrum; Pgr = postgenal ridge.

Fig.2: Scanning electron microscope images of cephalic parts of Opamyrma hungvuong worker, nontype (AKY05vii17-06, China, Guangxi). (A) anterior part of head in frontal view; (B) cranium in ventral view; (C) right mandible in dorsal view; (D) right hypostomal process in lateral view; (E) left mandible in ventral view; (F) labrum in outer view. Abbreviations: Ctl = canthellus; Hysp = hypostomal process; Occ = occipital carina; Lbr = labrum; Lps = labral peg-like seta; Mdl = mandalus; Mps = mandibular peg-like seta; Pat = preapical tooth; Ptg = peritorular groove; Ptp = posterior tentorial pit; Sca = supraclypeal area.

Fig.3: Maxillolabial complex of Opamyrma hungvuong worker, nontype (AKY05vii17-06, China, Guangxi). (A) Scanning electron microscope image of maxillolabial complex in ventral view, labrum removed; (B) right maxilla in outer view; (C) labium in lateral view; (D) labium in dorsal view. Abbreviations: Ams = anteromedian sclerite; Gcss = galeal crown’s stout seta; Hyp = hypopharynx; Lbp = labial palp; Lcn = lacinia; Mxco = maxillary comb; Mxp = maxillary palp; Mxst = maxillary stipes; Prm = prementum; Sglb = subglossal brush.

Fig.4: Tentorium of Opamyrma hungvuong worker,nontype (AKY05vii17-06, China, Guangxi). (A) anterior part of dorsal sclerite of cranium in dorsal view; (B) part of dorsal sclerite of cranium around right antennal socket with anterior part of tentorium, in inner ventral view; (C) part of ventral sclerite of cranium with posterior part of tentorium in inner dorsal view; (D) right half of tentorium in dorsal view (lacking posterior tentorial arm). Abbreviations: Ata = anterior tentorial arm; Atp = anterior tentorial pit; Ct = corpotendon; Dta = dorsal tentorial arm; Ep = external plate; Ip = internal plate; Lclp = lateral portion of clypeus; Mdb = mandible; Occ = occipital carina; Pgr = postgenal ridge; Pta = posterior tentorial arm; Ptg = peritorular groove; Ptp =posterior tentorial pit; Tb = tentorial bridge.

Fig.5: Scanning electron microscope images of antenna of Opamyrma hungvuong worker, nontype (AKY05vii17-06, China, Guangxi). (A) entire right antenna in dorsal view; (B) apical antennomere in dorsal view.

Fig.6: Scanning electron microscope images of mesosoma of Opamyrma hungvuong worker, nontype (AKY05vii17-06, China, Guangxi). (A) whole mesosoma in lateral view; (B) anterior articulation of mesonotum in lateral view, prothorax removed; (C) whole mesosoma in dorsal view; (D) whole mesosoma in ventral view, all legs removed; (E) metapleuron and propodeum in lateral view; (F) prosternite in ventral view, propleurae and prolegs removed. Abbreviations: Mgo = metapleural gland orifice; Mlf = metapleural longitudinal flange; Msg = mesonotal groove; Mstp = mesosternal pit; Mtsp = metanotal spiracle; Pcc = procoxal cavity; Pdl = propodeal lobe.

Fig.7: Scanning electron microscope images of legs of Opamyrma hungvuong worker,nontype (AKY05vii17-06,China, Guangxi). (A) strigil of right proleg in anterior view; (B) calcar of strigil of right proleg in anterior view; (C) strigil of right proleg in posterior view; (D) distitarsus of right proleg in posterior view;(E) tibial spurs and basitarsus of right mesoleg in anterior view;(F) tibialspurs and basitarsus of right metaleg in posterior view; (G) pretarsal claws of right metaleg in posteroventral view; (H) tibial spurs of left metaleg in anterior view.Abbreviations:Ats = anterior spur; Ca = calcar; Pts = posterior spur; Ptb = protibia;Pbts = probasitarsus; Ptss = protibial stout seta; Mnb = manubrium; Mstb = mesotibia;Msbts = mesobasitarsus;Mttb = metatibia;Mtbts = metabasitarsus.

Fig.8: Scanning electron microscope images of metasoma of Opamyrma hungvuong worker, nontype (AKY05vii17-06, China, Guangxi).(A) petiole inlateral view;(B) petiole inventral view;(C) helcium in anteriorview;(D) helcium in ventral view; (E) pretergite of abdominal segment IV in dorsal view; (F) gaster in lateral view; (G) gaster in ventral view. Abbreviations: Absg = abdominal segment; Prsn = presternite; Prtg = pretergite; Ptlt = petiolar laterotergite; Ptsn = petiolar sternite; Tss = tergosternal suture.

Fig.9: Sting apparatus of Opamyrma hungvuong worker, nontype (AKY05vii17-06, China, Guangxi). (A) spiracular plate in lateral view; (B) quadrate plate in lateral view; (C) anal arcs and anal plate in flattened dorsal view; (D) oblong plate and triangular plate in lateral view; (E) gonostylus in lateral view; (F) furcula in anterodorsal view; (G) furcula in posterior view; (H) sting in lateral view; (I) sting in dorsal view; (J) basal part of sting in lateral view; (K) Scanning electron microscope image of apical parts of sting and lancet in lateral view; (L) lancet and fulcral arm in lateral view. Abbreviations: Ana = anal arc; Anp = anal plate; Ap = anterior apodeme; Fa = fulcral arm; Gs = gonostylus; Lc = lancet; Ll = lateral lobe; Mc = medial connection; Pa = posterior arm; St = sting; Tp = triangular plate; Vc = valve chamber.