Chrysapace costatus

This species seems to be rare in the Shivalik range of Northwest Himalaya: the holotype was found in Forest Research Institute, Uttarakhand during intensive surveys. The specimen was found in leaf litter within a primary, subtropical, semi-evergreen forest with good annual precipitation.

Identification
Bharti and Wachkoo (2013) - This is an interesting species with remarkable costate sculpture, a character shared with only two Oriental species: Chrysapace jacobsoni and Chrysapace sauteri. Chrysapace costatus can be easily distinguished from C. jacobsoni by longitudinal costate sculpture of mesosoma and foveate gaster whereas latter is characterized by transverse costate sculupture on mesosoma and longitudinal costate sculpture on gaster. It separates from C. sauteri by rectangular head with porcate-sinuate sculpture and longitudinal costate sculpture on postpetiole while in C. sauteri head is subtriangular and sculpture is regular transverse costate on head and postpetiole.

Yamada et al. (2019) - In the worker, cranium subrectangular in full-face view, with costae on vertex strongly and coarsely distorted; eye and median ocellus relatively large (EI, 22–24; OI, 7–8; EI + OI, 29–31); dorsum of mesosoma longitudinally costate; abdominal tergite and sternite III longitudinally costate; abdominal tergite and sternites IV smooth with relatively dense hair-bearing foveae.

The original description of Chrysapace costatus stated that the worker of this species is easily distinguished from that of Chrysapace sauteri by “rectangular head with porcate-sinuate sculpture and longitudinal costate sculpture on postpetiole”. However, inconsistent with this original diagnosis, the characteristics of “rectangular head” and “longitudinal costate sculpture on postpetiole” are actually shared with Taiwanese C. sauteri. Nevertheless, the mainland Asian populations from Yunnan, Guangxi, and India differ from the Taiwanese population (= C. sauteri) in the following morphological characteristics of the worker: the former has more strongly and coarsely distorted costae on vertex of cranium, and larger eye and ocelli than the latter.

Distribution
Guangxi, China; India

Distribution based on Regional Taxon Lists
Oriental Region: India. Palaearctic Region: China.

Castes
Known only from the worker caste.

Nomenclature

 * . Cerapachys costatus Bharti & Wachkoo, 2013d: 1191, figs. 4-6 (w.) INDIA (Uttarakhand).
 * Type-material: holotype worker.
 * Type-locality: India: Uttarakhand, FRI (= Forest Research Institute), 30.3416°N, 77.9903°E, 640 m., 4.ix.2010, hand picking (A.A. Wachkoo).
 * Type-depository: PUAC.
 * Combination in Chrysapace: Borowiec, M.L 2016: 106.
 * Status as species: Bharti, Guénard, et al. 2016: 21; Borowiec, M.L. 2016: 106; Chen, Shi & Zhou, 2016: 8; Yamada, Lin & Eguchi, 2019: 478 (redescription).
 * Distribution: China, India.

Worker
TL 7.13; HL 1.23; HW 1.14; EL 0.28; WL 2.23; PL1 0.86; PW1 0.75; PL2 0.61; PW2 1.12; SL 0.80; GL 2.20. Indices: CI 92; SI 70; PI 87 (n = 1).

Head. Rectangular, slightly longer than broad, sides gently convex; vertex shallowly concave. Mandibles subtriangular, edentate. Antennae 12 segmented; scapes short and clavate; reaching up to 5/7th of posterior margin of head. Eyesmoderate, globular, protruded placed above the middle of head; 3 ocelli present. Anterior clypeal margin entire and convex; posterior margin deflexed and flat.

Mesosoma. Trunk shaped, wider posteriorly; dorsal profile convex; sutures absent except for distinct lateropronotal mesopleural suture. Propodeal declivity truncate; anterior border of dorsopronotum and propodeal junction marginate; mid and hind tibiae each have a large and small apical spur.

Metasoma. Petiole dorsally rectangular, longer than broad with convex sides; anterior face straight; dorsal profile convex. Postpetiole broader than long. Gaster elongate; base of cintus of first gastral tergite with cross ribs.

Sculpture. Head porcate-sinuate; malar space drab, clathrate; mandibles and scape covered with fine reticulations and scattered foveolae; funiculus microreticulate. Vertex, mesosoma, petiole and postpetiole costate-sulcate. Gaster foveate; gastral segments microreticulate.

Vestiture. Pilosity sparse, suberect; denser on scapes and legs; funiculus pubescent.

Color. Black with mandibles, antennae and legs castaneous.

Yamada et al. (2019) - Holotype worker. HL 1.23 mm; HW 1.07 mm; EL 0.27 mm; EW 0.20 mm; ES 0.24 mm; PEHL 0.28 mm; OL 0.07 mm; SL 0.81 mm; WL 1.97 mm; DML 1.59 mm; MW 1.06 mm; MFL 1.17 mm; PH 0.85 mm; PTL 0.87 mm; PTW 0.73 mm; A3L 0.88 mm; A3W 1.07 mm; CI 87; SI 76; EI 22; EPI 22; OI 7; DMI 67; DMI2 81; LMI 53; MFI 109; PTI 85; A3I 122.

Nontype workers (n=6). HL 1.10–1.17 mm; HW 0.90–0.97 mm; EL 0.23–0.26 mm; EW 0.17–0.21 mm; ES 0.21–0.23 mm; PEHL 0.24–0.29 mm; OL 0.06–0.08 mm; SL 0.65–0.70 mm; WL 1.60–1.77 mm; DML 1.25–1.32 mm; MW 0.85–0.89 mm; MFL 0.95–0.98 mm; PH 0.69–0.74 mm; PTL 0.68–0.73 mm; PTW 0.63–0.69 mm; A3L 0.74–0.82 mm; A3W 0.90–0.95 mm; CI 81–84; SI 70–74 ; EI 22–24; EPI 21–25; OI 7–8; DMI 67–70; DMI2 71–80; LMI 53–59; MFI 101–105; PTI 88–98; A3I 114–122.

Body color, pilosity, and structure are similar to the worker of Chrysapace sauteri except for the following characteristics: costae on vertex of cranium strongly and coarsely distorted; eye and ocelli relatively large (EI, 22–24; OI, 7–8; EI + OI, 29–31).

Etymology
The species epithet is Latin for costate, in reference to the distinguishing sculpture on mesosoma, petiole and postpetiole.

Determination Clarifications
Yamada et al. (2019) - Radchenko (1993) recorded a dealate queen from northern Vietnam as C. sauteri. Identity of this specimen is currently unknown, but the geographic range suggests its affinity with C. costatus.

References based on Global Ant Biodiversity Informatics

 * Yamada A., C. C. Lin, and K. Eguchi. 2019. Taxonomic notes on the rare ant genus Chrysapace with description of a new species from Brunei (Hymenoptera: Formicidae: Dorylinae). Acta Entomologica Musei Nationalis Pragae 59: 467-480.