Protanilla gengma Xu 2012
Creators: name: Griebenow, Zachary Hayes
name: Richter, Adrian
name: Economo, Evan P.
name: Dang, An Van
name: Yamada, Aiki
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Formicidae
Protanilla
Protanilla gengma

description: Protanilla gengma Xu, 2012
Figs 5–10
Protanilla gengma Xu, 2012: 485–486, figs 13–16.
Diagnosis
Worker
Cranium dark, conspicuously narrowed anteriorly. Mandible sublinear, with medial peg-like chaetae; dorsal lamella absent; laterodorsal longitudinal groove absent. Outline of clypeus campaniform, surface anteriorly concave; median clypeal ridge not visible. In dorsal view, PrW subequal to propodeal breadth. Mesotibia with one spur. Petiole sessile; anterior corner of dorsal petiolar node rounded in profile view; subpetiolar fenestra present. Abdominal segments II–III without tergotergal and sternosternal fusion; abdominal sternite III convex in profile view. Abdominal segments III–IV narrowly joined; anterior margin of abdominal tergite IV slightly emarginate in dorsal view.
Gyne
As for worker, but with compound eye.
Male
Distal 3 maxillary palpomeres subequal in length. Labial palp 2–3-merous. LF2 ≈ SL. Notauli present, scrobiculate. Hindwing 1A spectral to absent. Abdominal segment III petiolate. Length of abdominal postsclerites IV> combined length of abdominal postsclerites V–VIII. Cupula annular. Ventral penial process present.
Material examined
VIETNAM – Ninh Binh • 4 workers; Cuc Phuong National Park; 20.3496° N, 105.5957° E; 400 m a.s.l.; 8 Aug. 2022; M.G. Branstetter leg.; #4340; IEBR • 1 gyne; same data as for preceding; IEBR, CASENT0842884 • 30 larvae; same data as for preceding; IEBR, CSUENT6000161. – Bac Giang • 2 ♂♂; Tay Yen Tu Nature Reserve; 21.1792° N, 106.7228° E; 238 m a.s.l.; 30 Mar. 2003; K. Eguchi leg.; in rotten wood; Katsuyuki Eguchi personal collection, CSUENT6000018, CSUENT6000019 • 1 worker; same data as for preceding; CSUENT6000048 • 1 gyne; same data as for preceding; CSUENT6000047 • 1 worker; Tay Yen Tu Nature Reserve; 21.1697° N, 106.7183° E; 435 m a.s.l.; 27 May 2004; K. Eguchi leg.; Katsuyuki Eguchi personal collection, CASENT0179564.
Measurements and indices
Worker (n = 5)
HW = 0.46–0.49 mm; HL = 0.55–0.58 mm; SL = 0.48–0.52 mm; ML = 0.28–0.39 mm; WL = 0.91– 0.95 mm; PrW = 0.38–0.40 mm; MW = 0.27–0.29 mm; PTL = 0.29–0.35 mm; PTH = 0.38–0.39 mm; PTW = 0.21–0.23 mm; PPL = 0.26–0.30 mm; PPW = 0.25–0.27 mm; PPH = 0.39–0.40 mm; CI = 83–85; SI = 99–110; MI = 60–79; PI = 63–77; PPI = 86–95.
Gyne (n = 2)
HW = 0.53–0.55 mm; HL = 0.63–0.64 mm; EL = 0.05–0.06 mm; EW = 0.04 mm; SL = 0.53–0.56 mm; ML = 0.32–0.38 mm; WL = 1.05–1.07 mm; PrW = 0.45–0.46 mm; MW = 0.32–0.33 mm; PTL = 0.32– 0.36 mm; PTH (n = 1) = 0.45 mm; PTW = 0.27 mm; PPL = 0.28–0.30 mm; PPW = 0.30–0.35 mm; PPH = 0.46–0.47 mm; CI = 84–87; SI = 96–105 mm; MI = 61–69 mm; REL = 8–10; OI = 61–85; PI = 75–84; PPI = 108–118.
Male (n = 2)
HW = 0.64–0.65 mm; HL = 0.50–0.51 mm; EL = 0.27–0.28 mm; EW = 0.20–0.21 mm; SL = 0.17– 0.18 mm; LF2 = 0.16 mm; MaL = 0.06 mm; WL = 1.06–1.11 mm; PrW = 0.56–0.57 mm; MSW = 0.51– 0.58 mm; MSL = 0.54–0.55 mm; PTL = 0.22–0.23 mm; PTH = 0.20–0.22 mm; PTW = 0.18–0.19 mm; PPL = 0.22 mm; PPW = 0.24 mm; PPH = 0.25–0.27 mm; TW4 (n = 1) = 0.58 mm; CI = 124–132; SI = 27–28; MI = 16–17; OI = 74–75; REL = 53–57; MSI = 94–95; PI = 79–87; PPI = 107–113; TI1 (n = 1) = 46.
Description
Male
Head in full-face view suboval, wider than long (CI = 124–132); occiput entire. Mandibles reduced, nublike, edentate, articulated to cranium; mandalus large, occupying most of anterior half of mandibular dorsal surface. Labrum reduced. Palpal formula 4,3. Maxillary palpomeres II–IV elongate, each longer than maxillary palpomere I. Labial palpomeres II–III ~0.5× respective lengths of maxillary palpomeres II–III, respectively. Median clypeal length approximately 1.4× torular diameter; anterior margin weakly medially concave; posterior margin slightly produced between toruli. Anterior tentorial pit directly anterad antennal torulus in full-face view. Ocellar tubercle absent. Occipital carina present only dorsally. Compound eyes large (REL = 53–57), oval; all margins weakly convex. Antenna 13-merous, filiform; scape cylindrical, SL<EL or EW; pedicel subcylindrical, length a little less than 0.5× SL; antennomere III nearly as long as scape (LF2 = 0.16 mm; SL 0.17–0.18 mm).
In lateral view, anterodorsal face of pronotum depressed at transition to pronotal flange. Mesoscutum strongly convex, slightly longer than height or lateromedian breadth. Antero-admedian signum present. Notauli present, meeting at posterior mesoscutal margin. Parapsidal signa present, weakly impressed, slightly divergent anteriorly. Scutoscutellar sulcus deep and broad. Oblique mesopleural sulcus broad, scrobiculate, bisecting mesopectus. Mesoscutellar height and length subequal, posterodorsal mesoscutellar face convex, not posteriorly produced in lateral view; mesoscutellar disc wider than long; mesoscutellar dorsum high as that of mesoscutum. Metanotum strongly convex in lateral view, with dorsal face narrowly visible in dorsal view. Metapleural gland absent. Propodeum convex in lateral view, without distinct dorsal face; propodeal lobe absent. All legs similar, trochanters sphenoid (i.e., wedge-shaped), femora straight and somewhat anteroposteriorly compressed; proximodistal length of protrochanters ~1.5× as great as width, meso- and metatrochanters ~2× as great as width. Tibial spur formula 1b, 1p. Wing membranes hyaline. In forewing, C, Sc+R+Rs, Rf, Mf1, and 1A tubular; 2s-rs +Rs+4-6 spectral; M+Cu spectral; cu-a with weakening adjacent to 1A. Pterostigma present, large. Hindwing with R+Rs tubular, extending ¼ of distance along costal margin; 1A spectral, ~0.17× length of R+Rs.
Abdominal segments II–III petiolate, with complete tergosternal fusion and distinct tergosternal sutures. Abdominal segment II sessile, longer than wide (PI = 79–87), length and height subequal; lateral margins subparallel in dorsal view; abdominal tergite II convex, but petiole without dorsal node; in ventral view, abdominal tergite II subrectangular with rounded margins. Abdominal segment III wider than long (PPI = 107–113), 1.12–1.24× as high as long; post-tergite III weakly raised and convex posteriorly; abdominal poststernite III in lateral view with distinct rounded corner, outline of ventral margin sublinear. Abdominal segments IV–VIII without tergosternal fusion.
Spiculum present; abdominal sternite IX with robust posteromedian process. Cupula annular, lateromedial breadth slightly greater than maximum anteroposterior length; dorsum anteroposteriorly compressed. Gonopodites articulate. Gonocoxites with complete median fusion, with conspicuous sutures (“dgcs” and “vgcs” in Fig. 8C–D); gonocoxital arms fused to form anteromedian apodeme with acute apex, making ventral outline of gonocoxital foramen strongly emarginate in ventral view. Gonostylus a little shorter than gonocoxite, slightly recurved medially in dorsal view. Parossiculus lateromedially compressed, about 0.5 × as long as lateropenite; outline lobate in lateral view, with a few trichoid sensilla on apex. Lateropenite blunt, uncinate in lateral view, apex curved ventrad; ectal surface covered with dense basiconic sensilla; ventromesal margin with conspicuous lateral flange (Fig. 9E; “ltpf”). Penial sclerites without medial fusion, connected via dorsomedial conjunctiva; proximodorsally fused with gonocoxites, but connection weakly sclerotized. Preapical dorsum of penial sclerite bears conspicuous rounded lobes, produced laterad and mesad respectively (Fig. 9F–G; “lpl”, “mpl”); lateral lobe lamellate, relatively broad; mesal lobe thicker and narrower. Distodorsal part of penial sclerite smoothly tapering in lateral view, with downcurved apex subacute, ventral denticles absent. Proximoventral part of penial sclerite with long sawlike ventral process (“vpp” in Figs 8D, 9G) originating distal to lateral penial apodeme, produced ventrad and distad, recurved posterad at ~90° angle; in lateral view its distoventral and distodorsal margins bear ~ 58 small denticles; distal apex acute. Body dark brownish with paler antenna, mouthparts, and legs. Body sculpture mostly lacking; pronotal flange and anterior of abdominal postsclerites II–III coarsely longitudinally rugose; cinctus of abdominal segment IV scrobiculate. Somal pilosity as in Fig. 6.
Gyne
As for worker, completely lacking alar sclerites, but somewhat larger (WL = 1.05–1.07 mm) and with compound eye (Fig. 5B). Compound eye anteroposteriorly compressed, small (REL = 10), with 12 ommatidia.
Supplementary description
Worker
As in Xu (2012: 485–486), but with the following additions or differences. Labrum with three chaetae. Two rows of mandibular chaetae present, with 12 in dorsal row and 9 in ventral row; ventral row with chaetae expanded distally, except for most proximal chaeta. Subapical mandibular seta present. Palp formula 4,3. Tibial spur formula 1p, 1p.
Distribution
Further sampling is needed across the putative range of P. gengma to establish the scope of intraspecific variation. The specimens from Cuc Phuong National Park differ from the holotype in having three labral chaetae rather than four, as in the population of P. gengma reported from Mizoram, India (Aswaj et al. 2020). This and other differences between the holotype and the specimens reported here, along with those collected in Mizoram, are of unclear significance for species delimitation. The male of P. gengma closely resembles that of Protanilla TH 03, with the only apparent difference being palpomere count and coloration, with Protanilla TH 03 blackish, whereas P. gengma is browner; this variation may be intraspecific.
Ecology
The collections of Protanilla gengma reported here from Tay Yen Tu Nature Preserve are the first from rotten wood, rather than soil or leaf litter (Xu 2012; Aswaj et al. 2020). A pharate worker is here reported within a cocoon from collection #4340 at Cuc Phuong National Park, marking the first such record for Protanilla (Fig. 10A). This collection also contained 28 larvae feeding on a juvenile scolopendromorph centipede, consistent with behavior observed in other Leptanillinae. All larvae attached to the centipede were identical in size, therefore appearing to be in the same instar. The co-occurrence of a pharate adult and at least two larval instars would seem to argue against synchronous brood production in P. gengma.
Remarks
The contents of Eg03-VN-106 were reported by Eguchi et al. (2014: 23, figs 7–8) as Protanilla sp. eg-1, while CASENT0179564 was provisionally referred to as Protanilla VN 01 in preceding literature (Borowiec et al. 2019; Griebenow 2020; Griebenow et al. 2022). The 3-merous labial palp of both worker and male is exceptional among the Leptanillinae, amending the diagnosis for Protanilla and Leptanillinae for both forms. A 2-merous labial palp is implied to be an apomorphy of the Opamyrmini and Leptanilla. Without reexamination of Protanilla TH 03 we cannot confirm that the assessment of the labial palp as 2-merous in this male morphospecies (Griebenow 2020: fig. 10b) was accurate.
The description of the first known male belonging to the Protanilla bicolor species-group notably reveals an annular cupula, contrasting with the non-annular cupula of the Protanilla rafflesi species-group (Griebenow et al. 2023) and Opamyrma (Yamada et al. 2020). The annular cupula of Protanilla gengma, and its anterior separation from abdominal sternite VIII–IX and the gonocoxites, is a symplesiomorphy with at least one representative of the Leptanilla thai species-group (Leptanilla zhg-bt03) and the Leptanilla bethyloides species-group (Griebenow et al. 2023).
The ergatogyne here described is the first reproductive female documented for the Protanilla bicolor species-group. Unlike the ergatogynes known in at least one species of the Protanilla rafflesi species-group (Ito et al. 2022), alar sclerites are completely lacking in the ergatogyne of P. gengma. Most Protanilla gynes are alate, indicating that aptery in female reproductives has evolved at least twice in Protanilla, and moreover in different subclades.
description: Published as part of Griebenow, Zachary Hayes, Richter, Adrian, Economo, Evan P., Dang, An Van & Yamada, Aiki, 2025, Four new species of Leptanillinae (Hymenoptera: Formicidae) from northern Vietnam described with phylogenomics and micro-computed tomography, pp. 98-145 in European Journal of Taxonomy 987 on pages 109-116, DOI: 10.5852/ejt.2025.987.2867, http://zenodo.org/record/15255273