Stigmatomma scrobiceps

Guénard, Blanchard, Liu, Yang, and Economo (2013) - The two specimens were collected from a single site located at 550 meters elevation, consisting of secondary forest habitat with thick leaf litter cover and abundant decomposing woody material on the forest floor. The ants were collected from leaf litter using Winkler extraction. The peculiar morphology of the mandibles suggests a specialized predatory diet, like many other members of the Amblyoponinae (Gotwald and Levieux 1972, Ito 1993, Masuko 1993), but no direct observations have been made. Nothing else is currently known about the ecology of this species.

Identification
Guénard, Blanchard, Liu, Yang, and Economo (2013) - Although Stigmatomma mulanae is known from a single dealate queen, we believe that the workers described here represent a new species. The specimen of S. mulanae was not examined directly but the original description and drawings in Xu (2000) and photographs available on Antweb.org were used to compare specimens. The absence of developed frontal carinae in S. mulanae represents the most important characteristic. Other morphological characters in S. scrobiceps, such as the presence of well-developed clypeal conical setae, a clear separation of the frontal lobes, the shape of the scape, the presence of metapleural lobes, and the distinctive shape of the petiolar process further distinguish this species from the type specimen of S. mulanae. Finally, it should also be noted that the workers of S. scrobiceps are much larger than the queen of S. mulanae. The diagnosis presented here is susceptible to change with the description of the worker caste of S. mulanae.

Distribution based on Regional Taxon Lists
Palaearctic Region: China.

Known only from Yunnan Province, China.

Castes
Known only from the worker caste.

Nomenclature

 *  scrobiceps. Bannapone scrobiceps Guénard, Blanchard, Liu, Yang & Economo, 2013: 373, figs. 2-4 (w.) CHINA. Combination in Stigmatomma: Ward & Fisher, 2016: 691.

Worker
Holotype worker. HL 0.62 mm, HW: 0.64 mm, MaL: 0.54 mm, SL: 0.34 mm, TL: 3.30 mm, WL: 0.79 mm, PrW: 0.37 mm; MW: 0.22 mm; PdW: 0.28 mm; PW: 0.29 mm, PL: 0.18 mm, FCoW: 0.15 mm, FCoL: 0.28 mm; AIIIW: 0.41 mm; AIIIL: 0.21 mm; AIVW: 0.50 mm; AIVL: 0.22 mm.

Head: Head in full face view square-shaped (mandibles excluded), slightly wider than long and inflated on its anteromedian portion. Posterolateral corners round. Posterior margin flat with weak median emargination. Frontal lobes separated and elevated forming a deep impression of the posterior clypeal margin. Frontal lobe obscuring the inner lateral side of antennal socket. Clypeus with anterior margin slightly convex, dentate, bearing five distinct teat-like setae. The middle seta is larger than the two pairs of lateral setae. Anterolateral corner of head, near mandibular insertion, angular and lacking teeth. Eyes absent. Antennal scrobe well defined and moderately impressed, reaching almost to the posterior head margin. At about two third of the head length, the antennal scrobe depression bends at an angle of about 120 degrees. Frontal carina very long, reaching almost to the posterior margin of head, very well defined and elevated. The distance separating the frontal carinae increases along the antero-posterior axis of the head. Surface between the frontal carinae distinctively raised and forming a heartshaped region on the posterior part of the head. Mandible elongate, narrow and sickle-like, bearing 3 teeth on the masticatory margin. Apical tooth acute and very long, followed by two blunt teeth; with the median tooth less than 1/4 the length of the apical tooth; and the basal tooth less than half length of the median tooth. Irregular striate sculpture present on mandibles. Palps not visible on examined specimens; if present, then extremely reduced. Palp formula unknown. Antenna 11-segmented. Scape reaches almost two thirds of the head length. Scape narrows medially and widens apically, with apical fifth part weakly elbowed. Funiculus incrassate apically but not forming a distinct club. Apical antennal segment longer than combined length of preceding three segments.

Mesosoma. In lateral view, dorsum of mesosoma convex and continuous with a distinctly impressed groove posterior to the promesonotal suture. In dorsal view, mesonotum constricted. Pronotum wider than propodeum. Metanotal groove weakly impressed on the dorsum of mesosoma. In lateral view, propodeal declivity separated in two parts. The superior part of the propodeal declivity slightly concave and presenting a moderate slope, while posterior part of the propodeal declivity steeply sloping and concave. Propodeum unarmed. Propodeal spiracle circular and distinct, located at about two thirds of the superior part of the propodeum. Metapleural lobes large and rounded. Orifice of metapleural gland inconspicuous.

Coxa, femur and tibia of the forelegs much larger than those of the middle and hind legs. Single tibial spur present on fore and hind legs, absent on middle legs. Spurs are pectinate and without simple spur.

Metasoma. Petiole broad, thick, convex and low. Petiolar node longer than tall with anterior face straight and dorsal face slightly convex. In dorsal view petiole much broader than long. Subpetiolar process well developed and spoon-shaped without translucent fenestra. Petiole broadly attached to abdominal segment III. Abdominal segment III smaller than abdominal segment IV. Metasoma ending with a long and up-curved sting.

Sculpture: Head rugulose. Side of pronotum with shallow aerolae. Dorsal surface of pronotum transitioning from a densely striate sculpture anterioriorly to a sparser striate-punctulate sculpture posteriorly. Mesonotum and propodeum aerolate-rugulose in dorsal view. Propodeal pleurae with fine and sparse strigulations, with a general shiny appearance. Coxae smooth and shiny. Petiole with fine punctations. Abdominal segments without obvious sculpture but with a shiny appearance in both lateral and dorsal views.

Pubescence: Fine white long suberect hairs present on most of the body to a density ranging from sparse on the head and pronotum to very sparse on the mesonotum and propodeum. The rather long hairs gives an impression of dense pubescence. Hairs on head and pronotum mostly oriented anteriorly; hairs on abdominal segments III to VII oriented posteriorly. Petiole with very sparse pubescence. A few fine and longer erect hairs present on most parts of the body. A few erect hairs present on the scape.

Coloration. Mesosoma, metasoma and legs light yellow, head darker orange-brown.

Type Material
Holotype worker. CHINA: Yunnan, Xishuangbanna Dai Autonomous Prefecture, Mengla County, Xishuangbanna Tropical Botanical Garden, Tropical Rain Forest, 21°55'07.1N, 101°16'20.6E, 550 m elevation, leaf litter sifting (Winkler extractor method) (B. Guénard coll.), 5 June 2013, CASENT0339957. Paratype worker. Same data as the holotype, CASENT0340393. Due to the rarity of the Bannapone genus, the paratype is preserved in 99% Ethanol and was not mounted. Therefore no measurements were taken from this specimen. The holotype will be deposited at the Smithsonian National Museum of Natural History, Washington, DC, USA; a preserved paratype will be stored in the research collection of EPE, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan.

Etymology
The species name refers to the particular antennal scrobes observed on the head of the workers and derived from the latin “scrobis” (= trench) and “ceps” (= headed). The species epithet is an adjective that is invariant for gender.

References based on Global Ant Biodiversity Informatics

 * Guénard B., B. Blanchard, C. Liu, D. R. Yang, and E. Economo. 2013. Rediscovery of the rare ant genus Bannapone (Hymenoptera: Formicidae: Amblyoponinae) and description of the worker caste. Zootaza 3734(3): 371-379.
 * Liu C, B. Guénard, F Hita Garcia, S. Yamane, B. Blanchard, and E. Economo. New records of ant species from Yunnan, China. Submitted to Zookeys