Aquilomyrmex huangi

One of a number of described hell ant (Haidomyrmecinae) species, an ant lineage with remarkable, bizarre mandibles. The mouthparts of Haidomyrmecinae appear to be part of a now extinct morphological syndrome that evolved for specialized prey capture.

Identification
See the identification section for the genus and the description below.

Distribution
This taxon was described from.

Castes
Known from gynes.

Specimens
Originating from amber mines located near Noije Bum Village, Tanai Town, Myitkina District of Kachin State, northern Myanmar. A radiometric dating of zircons from the amber-bearing bed gave a maximum age of 98.79 ± 0.62 Ma (Shi et al., 2012), thus corresponding to the latest Albiane-earliest Cenomanian (mid-Cretaceous), which may not be very different from the age of the amber itself (Smith and Ross, 2018; Yu et al., 2019).

Holotype NIGP172000. Alate gyne. An almost complete specimen exposed in dorsal and ventral views, without distortion, with apical sclerite of gaster damaged and sting apparatus detached from the body. In a rounded piece of clear yellow amber measuring 15 x 13 x 3 mm, with few cockroach remains and numerous frass pellets and plant debris (wood fibers). NIGPAS, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Science, China.

Paratype NIGP171999. Alate gyne. A heavily distorted specimen exposed in dorsolateral views, displaying dorsoventral and lateral compression, and missing right antennomeres V-XII, left antennomeres II-XII, and the right hind leg beyond tibia. In a rounded piece of clear yellow amber measuring 16 x 3 mm. NIGPAS, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Science, China.

HA06. Alate gyne. A complete specimen exposed in profile views, with distinct distortion of the dorsum of head and promesonotum, with numerous bubbles or debris covering parts of head, wings and petiole. In a quadrangular piece of clear yellow amber measuring 11 x 5 x 4 mm, with a beetle (Coleoptera) and a midge (Diptera). HA, Huangyiren Amber Museum, Taiwan.

RM3. Alate gyne. A specimen exposed in profile views, with distinct longitudinal elongation, and missing left midleg, apical tarsormeres of left hind leg and gaster beyond third segment. In a round piece of amber measuring 15 x 4 mm, with a beetle, a fungus gnat and numerous insect and plant debris. RM, Ruipoxuan Museum, Jinan, China.

TJ41-020. Alate gyne. A nearly complete specimen exposed in profile views, with numerous bubbles contacting the body, and with partial wings detached and floating in the amber matrix close to the specimen. In a rounded piece of amber slightly obscured by a suspension of microscopic particles (‘dust’). Private collection of Tyler Janowitz

Nomenclature

 * †'†. †Aquilomyrmex huangi'' Perrichot, Wang & Barden, 2020: 10, figs. 2G-H, 5, 8C (q.) BURMESE AMBER (Myanmar, Cretaceous).

Queen
Holotype NIGP172000, [specimen RM3] (mm) HL (1.40) [1.33], HW (1.05), Hh (0.50); HoL (0.86); EL (0.56 in dorsal view); MDL (ca. 1.00); length of antennomeres: I (scape) (1.47) [1.80], II (pedicel) (0.16) [0.18], III-XII (0.25, 0.18, 0.16, 0.13, 0.13, 0.16, 0.13, 0.13, 0.13, 0.25); WL [3.50]; PL (0.61).

As for the genus, by monotypy.

Estimated body length around 9 mm. Cuticle smooth, densely covered by minute, adpressed setae, the pygidium additionally with dense, fine, erect setae.

Head prognathous, dorsoventrally flattened; in dorsal view, with lateral margins slightly converging posteriorly, occipital corners broadly rounded, posterior margin straight. Vertex elongate, nearly flat. Ocelli forming a small, weakly prominent triangle situated on vertex far posteriorly to posterior eye margins. Compound eyes large, oval, with outer margin only feebly extending beyond side of head laterally, situated dorsolaterally near anterior margin of head. Genae much reduced. Antennae inserted anteriorly to anterior margin of compound eyes, dorsally to base of clypeal horn, and immediately flanking lateral edges of a prominent frontal shelf; frontal shelf is distributed into a three-pronged projection comprising a median membranous support stalk, flanked by strong, turreted toruli partially concealing antennal bases in dorsal view; membranous stalk is flattened laterally, appearing as a slender line in dorsal view; in lateral view, stalk appears broad with conspicuous medial hole (potentially arising from desiccation; however, present in holotype and paratype), lower portion of stalk with ventral margin fused to the dorsal margin of the clypeal horn. Base of antenna with basal bulb exposed. Antenna geniculate, 12- segmented; scape long (SI 140), weakly arched in its basal half; pedicel short, 0.10 x scape length, less than twice as long as wide, broadened apically; antennomere III and XII longest flagellomeres, AIII cylindrical, about 3.6 x as long as wide, following flagellomeres gradually (weakly) increasing in width, apical flagellomere with rounded apex. Clypeal horn dorsoventrally flattened, protruding anteriorly (HoI 50), gently curved dorsally toward apex; with dorsal surface convex in profile view, ventral surface apparently concave; terminus of membranous horn bifurcated widely, with each bifurcation terminating in a subsequent bilobed pad; each pad with a small, medial, rounded lobe and a larger, lateral, rounded lobe, with tapered setae present along these lobes; lateral margins of horn connecting obliquely with anteroventral angles of head, just above mandibular insertion, by a cleared vertical cuticle, rimmed by short, thin, erect setae and occasional serrations. Labrum situated ventrally to horn, with to horn in size and shape except for apex only bifid (not each bifurcation bilobed; i.e., with the form of a snake tongue); ventral surface coated by short, darkened, thick, peg-like denticles on its basal half, additionally with sparse, long, fine, erect setae throughout. Mandibles sickle-shaped, inserted very close to compound eyes, lateral to hypostoma in ventral view; weakly spaced basally and converging apically, with tips acute and reaching to horn's apex between anterior median notch of labrum and clypeal horn; basal portion linear, directed ventrally; apical portion about 3 x as long as basal portion, curved dorsally approximately at 45° from basal portion, with dorsal surface apparently concave and smooth. Palps short, not reaching to occipital margin; maxillary palp with 5 visible segments, labial palp with 3 visible segments.

Mesosoma elongate, distinctly longer than high and wide. Pronotal neck pronounced, about as long as wide, 0.4 x as wide as maximal width of pronotal dorsum; pronotal dorsum distinctly lower than remaining mesosomal dorsum, with posterior margin strongly concave. Promesonotal suture present, complete. Mesoscutum in dorsal view shorter than pronotum (excluding neck), shorter than broad, with a distinct oblique anterior face forming a sharp angle with pronotal dorsum. Mesoscutal dorsal outline strongly convex, with faint parapsidal furrows converging posteriorly, almost reaching posterior mesoscutal margin. Mesoscutellum anteriorly flat, posteriorly strongly convex; anterior half bordered on each side by sharp carina converging posteriorly toward posterior convexity. Metanotum medially exposed in dorsal view, about half as long as mesoscutum. Propodeum convex, about as high as long, dorsal and declivitous surfaces forming a continuous curve; propodeal spiracle slit-like, situated high on sides, opening posteriad. Metapleural gland orifice a circular concavity at posteroventral margin of propodeum. Legs very long, slender. Mesocoxa only slightly shorter than procoxa, half as long as metacoxa. Small trochantellus present on mid- and hind legs. All femora distinctly swollen in their basal half, more than twice as broad as apical portion; ventral margin of each femur apically with two flange-like cuticular lobes flanking the base of tibia, these lobes increasingly larger from fore-to hind legs. Tibiae gradually increasing in width apicad. Dorsal surface of mid- and hind tibiae with a longitudinal row of 18-20 short, erect, stiff setae, and a paired row of long, erect, fine setae. Ventral margin of protibia apically with large calcar gently curved and one stout seta less than half as long as calcar; additionally the dorsal margin with three small, stiff setae. Mesotibia apically with two small, simple spurs; dorsal margin with 4 short, stiff setae. Metatibia apically with one long, pectinate spur and one short, simple spur; dorsal margin with 2 stiff setae. Tarsomere I of all legs elongate, longer than combined length of following tarsomeres II-V; tarsomere I of fore leg coated with longitudinal row of stiff setae on dorsal margin, and dense, short, fine, erect setae throughout; tarsomere I of hind leg very long, 0.8 x as long as tibia. Pretarsal claws with a distinct subapical tooth.

Fore wing with veins M∙f4 and Cu1 nebulous, not reaching wing margin; remaining veins tubular; cross-vein 1r-rs absent; Rs∙f1 faintly arched; M∙f1 distinctly arched, twice as long as Rs∙f1; Rs∙f2 nearly at right angle with Rs+M, half as long as M∙f2; Rs+M and M∙f2 not aligned, so that discal cell pentagonal, with vein 1m-cu distinctly longer than M∙f1; second submarginal cell long, crossvein 2rs-m situated far beyond apex of pterostigma; cross-vein cu-a arising from Cu, shortly distal to M∙f1. Hind wing with 14 distal hamuli, jugal lobe not visible, base of hind wing lost.

Metasoma. Petiole short-pedunculate, twice as long as broad; petiolar tergite a broadly convex node, with anterior and posterior surfaces subequal in length; posterior surface oblique in its basal half, horizontal in its distal half; broadly attached to base of first gastral tergite; subpetiolar process reduced to a small, laterally flattened rectangle present ventrally to petiole node ascent. First gastral segment bell-shaped; first tergite with helcium pronounced, forming a post-petiolar peduncle, with anterior surface posterior to helcium high, oblique, and dorsal surface strongly convex, short. Deep, girdling constriction between first and second gastral segments (abdominal segments III and IV). Second gastral segment distinctly longer than first, with deep lateral sulcus. Dorsum and lateral margins of pygidium coated in dense, tapered setae, hypopygium with long, sparse setae at terminus. Third valvula present. Sting present, strong.

Type Material
Holotype. NIGP172000, alate female. Paratype. NIGP171999, alate female. Additional specimens. HA06 and RM3, two alate females. Horizon and locality. Upper Cretaceous, Lower Cenomanian (ca. 99 Ma); in amber from the Hukawng Valley, Kachin State, Myanmar. Holotype and paratype - NIGPAS, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Science, China.

Etymology
The specific epithet is a patronym honoring Mr. Huang Yiren who provided four specimens for this study.