Linguamyrmex brevicornis, Perrichot & Wang & Barden, 2020

Perrichot, Vincent, Wang, Bo & Barden, Phillip, 2020, New remarkable hell ants (Formicidae: Haidomyrmecinae stat. nov.) from mid-Cretaceous amber of northern Myanmar, Cretaceous Research 109, pp. 1-18 : 13-16

Linguamyrmex brevicornis sp. nov.

urn:lsid:zoobank.org:act:D91488C6-3BEB-4A21-9F0E-3101BB9CCA85 .

Figs. 6CeE , 7 .

Etymology. The specific epithet is a combination of brevi (Latin, meaning ‘short’) and cornus (Latin, meaning ‘horn’), and refers to the smaller clypeal horn compared to the type species L. vladi .

Holotype. NIGP172001 , worker ( Figs. 6C , 7D ).

Additional specimens. LA01, alate female ( Figs. 6D , 7AeB ), and RM 4, worker ( Figs. 6E , 7C ).

Horizon and locality. Upper Cretaceous, upper Albianelower Cenomanian (ca. 99 Ma); in amber from the Hukawng Valley, Kachin State, Myanmar.

Diagnosis (females). Closely similar to L. vladi , but differs from this species by having a shorter clypeal horn (horn index HoI ¼ 31e 34 in L. brevicornis , 56 in L. vladi ), with stalk much reduced, slightly broader than long, with the setose pad more hexagonal and aligned with stalk (circular and with a distinct bend between stalk and clypeal pad in L. vladi ), and with clypeal pad coated in stout setae. It is also differentiated by the mandibles with two teeth on ventral corner of medioventral blade (teeth absent in L. vladi ) and, in workers, with the apical mandibular portion shorter than basal portion (apical portion longer in L. vladi ). In addition to the difference in the proportion of the mandible, the female castes of L. brevicornis differ by their size (body length ca. 7 mm in gyne, 4 mm in worker), by the antennae with flagellomeres compact in worker, more elongate in gyne, and by subpetiolar process present in worker.

Description (gyne). Total length of body around 7 mm. Cuticle minutely shagreened, densely covered by adpressed, minute setae, the apical gastral segments additionally with sparse pilosity of long, fine, erect setae becoming gradually denser toward apex.

Head. As in Linguamyrmex vladi , but with compound eyes slightly reniform, emarginate in middle of posterior margin. Ocelli distinct, positioned on a prominent cuticular triangle, in dorsal view, with posterior margin of lateral ocelli aligned with posterior margin of eyes. Antenna filiform, with flagellomeres elongate, cylindrical except apical one, which has acute tip; third antennomere twice as long as following one. Antennal sockets immediately flanking a medial frontal triangle that is sharply expanded anteriorly above clypeal horn, and connecting ventrally with dorsal surface of horn by a cleared, laterally flattened cuticle; frontal triangle projection terminates anteriorly at approximately same length as clypeal horn with slight indentation just dorsad clypeal horn, giving the appearance of a second, small, broadly rounded horn. Clypeal horn originating at base of frontal triangle, short and straight, in profile view almost perpendicular to longest axis of head. Horn paddle-shaped, with short, compact stalk and hexagonal, setose pad; stalk apparently glabrous, 0.10 mm in length, 0.12 mm in width; setose pad 0.26 mm in length, 0.20 mm at greatest diameter, with anterior margin straight, transverse; dorsal surface of setose pad glabrous, ventral surface densely and uniformly coated with very short, velcro-like vestiture; trigger hairs not visible. Lateral clypeal margins extending from above mandibular insertions toward horn as gently curved lines. Anterior clypeal margin broadly concave. Labrum visible. Mandible scythe-shaped; basal portion linear, short, meeting apical curved portion nearly at right angle; medioventral triangular blade bearing one large apical tooth and one small preapical tooth, with concave dorsal surface coated with pointed setae; apical portion of mandible posterior to medioventral blade 1.6 as long as blade, with tip broadly rounded. Mandibles preserved in closed position (with tips of apical portion reaching nearby clypeal setose pad), almost entirely parallel and closely approximated, except ventral corners of blades overlapping and tips slightly diverging. Maxillary palps 5-segmented, labial palps 3- segmented.

Mesosoma. Pronotal colar pronounced but not concealing entire propleuron in dorsal view; pronotal dorsum weakly convex. Promesonotal suture present, complete. In dorsal view, mesoscutum as long as pronotum (excluding neck), about as broad as long, with lateral and posterior margins carinate; posterior mesoscutal margin broadly concave; dorsal mesoscutal surface with long parapsidal furrows almost reaching anterior mesonotal margin, converging posteriorly but not touching. In profile view, pronotal dorsal outline feebly convex, mesoscutal dorsal outline nearly flat. Mesoscutellum prominent posteriorly; posterior mesoscutellar surfaces concave, their junction forming a sharp angle; dorsal mesoscutellar surface with a deep, broad, transverse groove immediately posterior to scuto-scutellar suture. Metanotum medially as high as long, with posterior surface forming distinct angle with pronotal dorsum. Propodeum 1.3 as high as long; in profile view, propodeal dorsum distinctly lower than pronotal dorsum; propodeal dorsum nearly flat, declivitous surface feebly convex, their junction broadly rounded. Propodeal spiracle slit-like, oriented posteriad. Metapleural gland opening circular, gaping. Legs long and robust, mesocoxa distinctly shorter than pro- and metacoxae; small trochantellus present on mid- and hind legs; all femora distinctly swollen in their basal half, tibiae swollen in their apical half; ventral margin of protibia apically with large calcar and two simple, stout setae less than half as long as calcar; mesotibia apically with two long, straight, pectinate spurs, and two short, straight, stout setae; metatibia apically with one long, pectinate spur and one long, simple spur. Tarsomeres IeIV of all legs with pairs of stout setae along entire ventral surface (8e10 pairs on tarsomere I, 4e5 pairs on tarsomere II, 3 pairs on tarsomere III, 2 pairs on tarsomere IV), and apically with 2 pairs of stout setae each flanking a spatulate spine; additionally the ventral surface of tarsomeres IeIV covered by dense brush of fine, erect setae; pretarsal claws thick, 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 þ M, half as long as M∙f2; Rs þ 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 jugal lobe present.

Metasoma. Petiole short-pedunculate; petiolar tergite forming a broadly convex node, with anterior surface approximately twice as long as posterior surface; subpetiolar process present, in profile a high, transverse, tooth pointing ventrally, with anterior surface concave, posterior surface vertical; transverse sulcus visible across petiole near basal margin. First gastral segment with helcium pronounced, forming a post-petiolar peduncle, with anterior surface posterior to helcium high, oblique, and dorsal surface strongly convex, short; anteriormost part of first gastral sternite with a distinct mesal process pointing anteroventrally below helcium. Second gastral segment distinctly longer than first, with presclerite largely exposed to form a deep, broad constriction between first and second gastral segments (abdominal segments III and IV). Posterior margin of gastral segments II onward with sparse, elongate setae. Pygidium nearly glabrous while hypopygium with sparse setae; pygidium apparently broadly acute towards sting shaft.

Wingless female (worker). Smaller than gyne (total length of body around 4 mm), and with the following differences: compound eyes oval, ocelli faintly visible, not positioned on a prominent cuticular triangle. Antenna more compact, with flagellomeres IIeIX gradually broadened apically, apical flagellomere with rounded apex. Clypeal setose pad more quadrangular, the ventral surface with a pair of trigger hairs originating at pad base. Mandible with medioventral triangular blade larger and apical portion (posterior to blade) reduced, 0.6 as long as blade.

Mesosoma and metasoma as in L. vladi except propodeum higher than long, petiole with subpetiolar process present, and girdling constriction deeper between abdominal segments III and IV (AIII with an oblique posterior surface). Protibia with one large apical spur (calcar) and two short stout setae; mesotibia with two simple spurs and three conspicuous setae positioned along anterior margin of tibial apex; metatibia with one pectinate and one simple spur, additionally with a brush of 8e10 setae flanking the pectinate spur. Sparse, erect setae positioned on dorsum of pronotum, propodeum, petiolar tergite, and first and second gastral tergites and sternites. Pygidium not preserved.

Measurements (in mm) (worker holotype NIGP172001) [worker specimen RM4] {gyne specimen LA01}. HL [0.82] {0.82}; EL [0.21] {0.42}; HoL [0.17] {0.36}; MDL [0.59] {0.80}; length of antennomeres: I (scape) (0.57) [0.67] {1.04}, II (pedicel) (0.09) [0.12] {0.14}, III-XII (0.35, 0.17, 0.16, 0.15, 0.15, 0.13, 0.13, 0.12, 0.13, 0.17) {0.80, 0.40, 0.34, 0.32, 0.31, 0.30, 0.30, 0.32, 0.32, 0.35}; WL [1.29] {2.29}; PL {0.70}.

Figures

Fig. 6. Representative females of Protoceratomyrmex revelatus gen. et sp. nov. (AeB) and Linguamyrmex brevicornis gen. et sp. nov. (CeE). Habitus (A) and head (B) of worker holotype NIGP172002.Habitus of worker holotype NIGP172001 (C), head of gyne specimen LA01 in dorsal view (D), head of worker specimen RM4 (E) in lateral view. Abbreviations: cp, clypeal process; ft, frontal triangle; ts, trigger setae. Scale bars: 1 mm (A, C), 0.25 mm (B, D, E).

Fig. 7. Overview and details of females of Linguamyrmex brevicornis gen. et sp. nov. Gyne specimen LA01 (AeB), worker specimen RM4 (C), worker holotype NIGP172001 (D). Habitus (A, C), head and mesosoma in dorsal view (B), head in ventrolateral view (D). Scale bars: 0.5 mm.