Leptanilla belantanoides, Griebenow & Richter & Economo & Dang & Yamada, 2025

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, European Journal of Taxonomy 987, pp. 98-145 : 124-129

Leptanilla belantanoides sp. nov.

urn:lsid:zoobank.org:act:8BBE61F2-2D95-41EB-B7A0-857E40222303

Figs 14–15

Surface mesh of worker: https://sketchfab.com/3d-models/casent0745758-leptanilla-belantanoidesworker-27a618e409664d6e874cbd978d73f163

Diagnosis

Worker

Mandible with four teeth, basal tooth truncate; short relative to head. Scape short relative to head. Flagellum submoniliform. Clypeal process present, apex emarginate. Length of subapical tapering seta <½ ML. Maxillary palp 1-merous. PrW>MW. Pronotal and mesonotal heights of dorsa subequal. Meso-metapleural suture absent. Anterior margin of abdominal segment II linear in dorsal view. Subpetiolar process present, not lamellate. PTL<PPL. Abdominal sternites II–III projecting comparably ventrad craniocaudal axis. PPW <½ TW4. Length of abdominal postsclerites IV greater than combined length of abdominal postsclerites V–VIII.

Male

Mandibles inarticulate. Clypeus distinct, extending between toruli; antennal sockets not placed on anterior cranial shelf. LF2 and ML>SL. Ocelli present, situated on tubercle; anteromedian ocellus directly dorsad compound eyes in profile view. Distal transverse carina absent from procoxa; protrochanter sphenoid; profemur arcuate, arcuate medial carina and apicoventral hook absent; ventromedian carina and cuticular comb absent from protibia. Pronotum and mesoscutum not anteroposteriorly prolonged. Mesoscutellum without posterior process. Forewing M +Cu absent. Metapleuron distinct from metapectal-propodeal complex. Propodeal declivity concave in profile view. Petiole without distinct dorsal node. Abdominal tergite VIII broader than long in posterodorsal view. Mulceators absent. Gonopodites inarticulate, with ventral suture; gonocoxites without dorsomedian fusion; gonostyli present, ventral margins entire and not dorsad ventral gonocoxital margins. Volsellae present, medially separate; apex furcated. Penial sclerites dorsoventrally compressed, medially fused; phallotreme dorso-apical, without setal vestiture.

Etymology

The specific epithet means ‘like belantan ʼ, referring to Leptanilla belantan , a closely related species. The gender of the specific epithet is neuter.

Type material

Holotype

VIETNAM – Ninh Binh • worker; Cuc Phuong National Park , 150 m NW of central parking lot; 20.3492° N, 105.5970° E; 392 m a.s.l.; 8 Aug. 2022; A. Richter leg.; clay soil by rotten log, ~ 2 cm deep; ARVI0042; IEBR, CSUENT6000061 .

Paratypes

VIETNAM – Ninh Binh • 4 workers; same data as for holotype; IEBR, CASENT0842867 , CASENT0842878 , CASENT0842879 , CASENT0842881 .

Other material examined

VIETNAM – Ninh Binh • 2 workers; same data as for preceding; IEBR, CASENT0842880 , CASENT0842882 • 1 ♂; Cuc Phuong National Park , headquarters; 20.25014° N, 105.70469° E ± 6 m; 190 m a.s.l.; 7 Aug. 2022; P.S. Ward leg.; PSW18689-01; UCDC, CASENT0842868 • 1 ♂; same data as for preceding; IEBR, CASENT0842869 • 1 ♂; Cuc Phuong National Park , headquarters; 20.24790° N, 105.70871° E ±4 m; 160 m a.s.l.; 7 Aug. 2022; P.S. Ward leg.; PSW18688-01; P.S. Ward personal collection, CASENT0883690 .

Measurements and indices

Holotype

HW = 0.31 mm; HL = 0.41 mm; SL = 0.25 mm; ML = 0.17 mm; WL = 0.52; PrW = 0.21 mm; MW = 0.15 mm; PTL = 0.12 mm; PTH = 0.11 mm; PTW = 0.10 mm; PPL = 0.10 mm; PPW = 0.10 mm; PPH = 0.14 mm; TW4 = 0.30 mm; CI = 76; SI = 81; MI = 55; PI = 83; PPI = 100; TI1 = 33.

Workers

HW = 0.31–0.32 mm; HL = 0.40–0.41 mm; SL = 0.24–0.26 mm; ML = 0.16–0.17 mm; WL = 0.51– 0.53 mm; PrW = 0.18–0.20 mm; MW = 0.13–0.15 mm; PTL = 0.11–0.13 mm; PTH = 0.11–0.12 mm; PTW = 0.08–0.10 mm; PPL = 0.09–0.10 mm; PPW = 0.09–0.10 mm; PPH = 0.14 (n = 4); TW4 = 0.28–0.30 mm; CI = 75–79; SI = 75–85; MI = 51–55; PI = 65–93; PPI = 91–106; TI1 = 32–36.

Male

HW = 0.36 mm; HL = 0.23 mm; SL = 0.11 mm; LF2 = 0.15 mm; MaL = 0.04 mm; ML = 0.06 mm; EW 0.16 mm; EL = 0.13 mm; WL = 0.65 mm; MSW = 0.32 mm; MSL = 0.33 mm; PTL = 0.08 mm; PTH = 0.16 mm; PTW = 0.17 mm; CI = 158; SI = 30; MI = 17; OI = 82; REL = 56; MSI = 98; PI = 206.

Description

Worker

Lateral margins of cranium moderately convex. Occipital carina distinct. Clypeal process present, delimited from cranium by lateral carinae, with posteromedian delimitation from cranium by Λ-shaped signum, projecting well anterior of labrum in full-face view; apex robust, broad in outline, linear, bordered by laminae. Mandible short relative to head; four teeth present; basal tooth large, blunt, not enlarged apically nor distally recurved. Large, tapering basal seta absent from mandible; subapical tapering seta present, only slightly longer than surrounding setae,<½ ML. Maxillary palp 1-merous. Pedicel length subequal to that of basal flagellomere. Flagellum submoniliform; antennomere 3 subequal in length to distal antennomeres; apical flagellomere>2× as long as subapical flagellomere. In dorsal view, pronotal margins strongly convex, pronotal width distinctly greater than mesonotal width (PrW = 0.18–0.21 mm; MW = 0.13–0.15 mm). Pronotal dorsum slightly convex, elevation equal to that of dorsal mesonotal vertex. Lateral margins of mesonotum and metapectal-propodeal complex subparallel in dorsal view; mesonotum not constricted anteriorly. Meso-metapleural suture absent; fusion of mesonotum with propodeum marked by shallow excavation. Bulla extending anterad propodeal spiracle. Propodeum angular in profile view; propodeal declivity slanted; posterolateral corners rounded. Tarsomeres longer than broad. Meso- and metatibial spur formula 2b,2(1b,1p). Anterior margin of petiole linear in dorsal view. Abdominal segment II longer than wide, with distinct dorsal node; margins parallel in dorsal view; subpetiolar process present, not lamellate, anterior face concave in profile view. Abdominal segment III longer than wide in dorsal view. Breadth of abdominal segment III less than half the breadth of abdominal segment IV in dorsal view. Anteroposterior length of abdominal tergite IV greater than that of V–VIII combined. Mesopectus and ventral surface of petiolar sternite without reticulate sculpture. Coloration castaneous.

Male

Cranial outline subspherical (CI = 158). Occiput entire. Frons not produced into anterior shelf. Mandible fused to gena; broader than long. Mandalus large, covering entire ectal mandibular surface. Maxillary palp 2-merous, palpomeres indistinct. Clypeus extending posteriorly between antennal toruli, discernible in full-face view. Anterior tentorial pits situated anterad antennal toruli. Compound eyes wider than long in profile view (OI = 82), large (REL = 56), outline subcircular, all margins entire. Anteromedian ocellus and compound eyes both intersecting line drawn perpendicular to anteroposterior axis of cranium. Scape subcircular in cross-section, longer than wide, SL<EL; pedicel short, vasiform, length 0.5× SL; antennomere 3 long, cylindrical, length greater than that of scape (SL = 0.11 mm; LF2 = 0.15 mm); flagellum filiform, extending posterior to mesoscutum if folded flat over mesosoma. Pronotum and mesoscutum not anteroposteriorly prolonged. In profile view anterodorsal pronotal face diagonal to craniocaudal axis at ~45° angle. Mesoscutal dorsum convex, projecting anteriorly dorsad pronotum; mesoscutum longer than broad. Antero-admedian signum present. Notauli absent. Parapsidal signa present, impressed. Mesoscutellum as tall as long, dorsum higher than that of mesoscutum, posterodorsal mesoscutellar face convex, not posteriorly produced or recurved. Oblique mesopleural sulcus present, not intersecting metapectal-propodeal complex. Metapleuron distinct, juncture between upper and lower metapleuron narrow. Metapleural gland absent. Propodeum concave in profile view, with outline sinuate. Coxal lengths subequal, with procoxal length greatest. Procoxa without distal transverse carina. Protrochanters sphenoid in outline, distally truncate. Profemur slightly curved, with proximal dorsoventral margins converging in lateral view, not anteroposteriorly compressed; acute distal flange on ventral surface absent; arcuate medial carina absent. Protibia slightly shorter than profemur; not dorsoventrally compressed, without ventromedian carina; protibial comb absent; probasitarsal seta smaller than calcar. Spur formula 2b,2b. C and Sc +R+Rs fused, tubular; 2s-rs +R+4-6, Rsf1, Mf1, and M +Cu nebulous; all other venation absent. Costal infuscation absent. Abdominal segment II anteroposteriorly compressed, broader than long in dorsal view (PI = 206), excluding presclerites; dorsal node absent; without median dorsal excavation. Abdominal sternite II without process, convex in profile view. Presclerites of abdominal segments III–VIII inconspicuous. Abdominal segments III–VII without tergosternal fusion. Tergosternal fusion of abdominal segments VIII–IX unknown. Abdominal tergites III–VII anteroposteriorly compressed, lateral margins subparallel or converging; breadth of abdominal tergite VIII subequal to that of abdominal tergite VII in posterodorsal view. Abdominal sternites VIII– IX not visible without dissection. Mulceators absent. Gonopodite inarticulate. Gonocoxites without complete dorsomedian and ventromedian fusion; gonocoxital lamina absent. Gonostylus present, recurved medially, with expansive dorsal laminae; apex entire. Volsella present, transected by articulatory sulcus; bifid, with dorsal process sharply curving laterally, ventral process moderately curving laterally, apex extending distad that of dorsal process. Penial sclerites dorsoventrally compressed, not basally recurved, dorso- and ventromedian carinae absent, lateral margins laminate. Penial apex with deep median incision, phallotreme at proximal extremity of incision. Phallotreme dorsal, apical, not recessed, not surrounded by vestiture of setae. Most sclerites with vestiture of subdecumbent setae; elongated on posterior margins of abdominal tergites VII–VIII; ventral face of volsella distad articulatory sulcus with long, suberect setae; gonostylus with decumbent setae, longer than on soma; genitalia otherwise bare. Cuticle bearing piligerous punctae; sculpture otherwise absent.

Distribution

Known only from Cuc Phuong National Park.

Ecology

Little is definitively known, or can be speculated, regarding the ecology of Leptanilla belantanoides sp. nov. The habitation of this species in soil is unremarkable for Leptanilla .

Remarks

Leptanilla belantanoides sp. nov. appears most similar to L. belantan from peninsular Malaysia and Leptanilla sapa sp. nov., with the shape of the proximal mandibular tooth being intermediate in L. belantanoides between these two species, and its length proportionally shorter than in L. belantan . Emargination of the clypeal process is also less pronounced in the worker caste of L. belantanoides than in either of these relatives. Further sampling of worker members of the Leptanilla thai species-group across mainland southeast Asia, and collection of the corresponding males, will clarify the boundaries between these species.

In the male-based key to the Leptanilla thai species-group of Griebenow (2024: 162), Leptanilla belantanoides sp. nov. keys out to the second lug of couplet 9. It is distinguished from Leptanilla zhg-th05 in that the ventral gonostylar margin is entire, without any projecting angle; and that the ventral gonopodital suture is not coincident with an abrupt ledge. As in Leptanilla zhg-th05 and several other male morphospecies within the Leptanilla thai species-group, the dorsoventral margins of the male profemur in Leptanilla belantanoides converge proximally, giving the profemur an arcuate outline in profile ( Griebenow 2024: fig. 42A). We predict that the male profemur of Leptanilla belantanoides serves a grasping function in copula.

Leptanilla belantanoides sp. nov. is here confirmed to belong to the Leptanilla thai species-group by phylogenomic inference. Beyond L. belantan and Leptanilla sapa sp. nov., among the putative members of the Leptanilla thai species-group for which the worker caste is known, L. belantanoides appears is most closely similar to Leptanilla ujjalai Saroj et al., 2022 and the undescribed Leptanilla zhg-th02. Males are unknown for these relatives of L. belantanoides , and none have yet been sequenced. All are united in possessing a truncate proximal tooth on the worker mandible, ventrad the masticatory margin.

The Leptanilla thai species-group, equivalent to the former genus Yavnella , was originally described from male specimens ( Kugler 1987), with the worker caste being heretofore definitively identified only for Leptanilla laventa ( Griebenow et al., 2022) . The male is unknown in both these species, meaning that L. belantanoides is the first member of the Leptanilla thai species-group for which the worker and male are associated (in this case by UCEs). The male morphospecies that most closely resemble those of L. belantanoides sp. nov. are all undescribed.

Figures

Fig. 14. Leptanilla belantanoides sp. nov., holotype, worker (CSUENT6000061). A. Profile view. B. Dorsal view. C. Full-face view. Scale bars = 0.25 mm.

Fig. 15. Leptanilla belantanoides sp. nov., male (CASENT0842869). A. Profile view. B. Dorsal view. C. Full-face view. Scale bars: A = 0.2 mm; B = 0.5 mm; C = 0.01 mm.