Syscia chaladthanyakiji

The type series from western Thailand and a colony from eastern Thailand was found nesting in rotting wood on the forest floor. This new species inhabits primary forests from lowland to highland (250–1000 m).

Identification
Jaitrong, Wiwatwitaya, and Yamane (2020) - Syscia chaladthanyakiji is similar to a Sri Lankan species, Syscia typhla, in general appearance of workers. However, S. chaladthanyakiji is separated from S. typhla by 1) in dorsal view, petiole and postpetiole almost as long as broad (clearly longer than broad in S. typhla); 2) with mesosoma in profile view, dorsal outline straight (weakly convex in S. typhla); 3) head relatively shorter (CI 80–84 in S. chaladthanyakiji; CI 70 in S. typhla); 4) stronger sculpturing than in S. typhla.

Distribution based on Regional Taxon Lists
Oriental Region: Thailand.

Nomenclature

 * . Syscia chaladthanyakiji Jaitrong, Wiwatwitaya & Yamane, 2020b: 3, figs. 1-6, 11 (w.q.) THAILAND.
 * Type-material: holotype worker, 29 paratype workers.
 * Type-locality: holotype Thailand:Tak Prov., Umphang Dist., Thung Yai Wildlife Sanctuary, Kangae Ki, Head Quarter, 26.ii.2016, colony no. TH16-WJT-0145 (W. Jaitrong); paratypes: 20 workers with same data, 9 workers with same data but TH16-SKY-113 (Sk. Yamane).
 * Type-depositories: TNHM (holotype); SKYC, TNHM (paratypes).
 * Distribution: Thailand.

Worker
Holotype: HL 0.66; HW 0.53; SL 0.30; MW 0.43; ML 0.86; PL 0.33; PH 0.36; PW 0.33; PPL 0.46; PPH 0.43; PPW 0.46; CI 80; SI 56; PI1 91; PI2 100; PPI1 108; PPI2 100; WI 140. Paratype workers (n = 10): HL 0.56–0.66; HW 0.46–0.53; SL 0.26–0.33; MW 0.36–0.43; ML 0.76–0.86; PL 0.26– 0.33; PH 0.30–0.36; PW 0.26–0.33; PPL 0.40–0.43; PPH 0.36–0.43; PPW 0.40– 0.46; CI 80–84; SI 56–63; PI1 89–91; PI2 100; PPI1 100–109; PPI2 100–108; WI 130–150.

Size and color. Medium size (HW 0.46–0.50 mm; ML 0.76–0.86 mm). Body entirely reddish brown; antenna, legs and tip of gaster yellowish brown. Hairs yellowish brown. Structure. Head in full-face view rectangular, slightly longer than broad with almost parallel sides; posterior margin weakly concave. Antenna 11-segmented with enlarged apical segment (XI) which is longer than VI–X combined; scape short, not reaching mid-length of head in full-face view; antennal segment II almost as long as broad; III–VI broader than long. Frontal carinae short and narrow, reaching less than half length of head, with head in profile sharply elevated in anterior half, low and vestigial in posterior half. Clypeus short, its anterior margin almost straight. Compound eye and ocelli completely absent. Mandible triangular, its masticatory margin feebly concave and edentate. Mesosoma rather elongate, subrectangular, seen from above almost parallel-sided; in profile view, dorsal outline of mesosoma straight; promesonotal suture and metanotal groove absent; mesopleuron demarcated from lateral face of pronotum and mesonotum by a distinct suture, but not clearly demarcated from metapleuron. Propodeum relatively long; declivity feebly concave, encircled with a thin rim. Petiole in dorsal view rectangular, slightly longer than broad, almost parallel-sided; in profile view, petiolar node (excluding sternite) longer than high, subrectangular, with weakly convex dorsal outline; subpeiolar process in profile view, subrectangular with its ventral outline concave. Postpetiole in dorsal view clearly larger than petiole, subrectigular, slightly longer than broad; in profile view longer than high, its dorsal outline weakly convex; postpetiolar sternite in profile view low, with ventral margin almost straight, anteroventrally produced as a blunt angle directed downward and forward. Abdominal tergite IV (= first gastral tergite) elongate, in dorsal view almost parallel-sided, its anterior margin almost straight.

Sculpture. Entire body densely with well-defined macropunctures. Antennal scape, outer face of mandible and legs with dense fine micropunctures. Legs slightly smooth and shiny.

Pilosity. Body entirely covered with short decumbent and standing hairs.

Queen
Dealate. HL 0.66; HW 0.56; SL 0.33; MW 0.56; ML 1.06; PL 0.36; PH 0.36; PW 0.36; PPL 0.46; PPH 0.46; PPW 0.50; CI 85; SI 59; PI1 100; PI2 100; PPI1 100; PPI2 107; WI 136.

Similar to worker in structure, sculpture and pilosity, with the following conditions that should be noted: body slightly larger; head in full-face view subrectangular, slightly longer than broad; eye present, relatively large, its length almost as long as distance between mandibular base and anterior margin of eye; median ocellus as large as lateral ocelli and located at the level of posterior margin of eyes; mesosoma massive and long, in profile view, with almost straight dorsal outline; mesopleuron broad, demarcated from pronotum and mesopleuron by shallow sutures, without oblique mesopleural sulcus; propodeum relatively short; in dorsal view, pronotum relatively long, with anterior margin roundly convex, posterior margin strongly concave, and lateral margins parallel; parapsidal line distinct but relatively short; mesoscutum flat, trapezoidal, its anterior margin strongly convex, while posterior margin almost straight; mesoscutellum subrectangular, almost as long as propodeum; metanotum very short, represented as a ridge; petiole square, with almost parallel lateral margins; postpetiole subrectangular, slightly longer than broad and broadened posteriorly.

Type Material
Holotype – worker (THNHM-I-05483, ), W Thailand: Tak Province, Umphang District, Thung Yai Wildlife Sanctuary, Kangae Ki, Head Quarter, 26.II 2016, W. Jaitrong leg., Colony no. TH16-WJT-0145. Paratypes: twenty workers, same data as holotype (THNHM-I-05484, THNHM-I- 19536 to THNHM-I-19551, and THNHM-I-20300 to THNHM-I-20302,, , THNHM); nine workers, same colony as holotype collected by Sk. Yamane, TH16-SKY-113 (SKYC, THNHM).

Etymology
The specific name is dedicated to Mr. Chaiyarest Chaladthanyakij (Uthaiwitthayakhom School, Thailand), who helped us in ant collecting in Uthai Thani and Tak Provinces.