Chrysapace merimbunensis

This species is only known from the type locality, Tasek Merimbun (Brunei, Tutong).

Identification
Yamada et al. (2019) - In the worker, cranium subtrapezoidal in fullface view; dorsum of mesosoma longitudinally costate; abdominal tergite III with costae which are transversely arched around center of posterior margin in dorsal view; abdominal sternite III longitudinally costate; cinctus of abdominal segment IV smooth without any costae; abdominal tergite and sternites IV smooth with sparse hair-bearing foveae.

Chrysapace merimbunensis is relatively similar to Chrysapace sauteri and its sibling species Chrysapace costatus by sharing the following characteristics of the worker:
 * dorsum of mesosoma, petiolar tergite, and abdominal sternite III longitudinally costate
 * abdominal tergite IV–VI lacks any costation

However, the worker of the former is easily distinguished from those of the latter two species by subtrapezoidal shape of cranium in full-face view, non-costate posterodorsal face of helcium, abdominal tergite III with costae which are transversely arched around center of posterior margin in dorsal view, and non-costate cinctus of abdominal segment IV.

In this genus the male was previously described only for C. sauteri. Our comparison of the male morphology of C. merimbunensis and C. sauteri highlights that the male genitalia are highly differentiated between these species, especially in the shape of posterior spines and posteromedian flange of abdominal sternite IX, shape of posterodorsal projection of basimere, thickness of articulation of basimere and telomere, shape of telomere, shape of digitus, and shape of valviceps. These characters are likely to be useful for taxonomy at the species level.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Brunei Darussalam.

Castes
The queen of C. merimbunensis is currently unknown.

Nomenclature

 * . Chrysapace merimbunensis Yamada & Eguchi, in Yamada, Lin & Eguchi, 2019: 469, figs. 1-19 (w.m.) BORNEO (Brunei).
 * Type-material: holotype worker, 1 paratype worker, 3 paratype males.
 * Type-locality: Brunei: Tasek Merimbun, Tutong, 17.viii.1999, Eg99-BOR-590 (K. Eguchi).
 * Type-depositories: MBSB (holotype); MBSB, MHNG (paratypes).
 * Distribution: Brunei.

Worker
Holotype worker (paratype worker in the parentheses). H L 1.63 (1.57) mm; HW 1.56 (1.50) mm; EL 0.39 (0.38) mm; EW 0.27 (0.27) mm; ES 0.33 (0.32) mm; PEHL 0.28 (0.24) mm; OL 0.05 (0.04) mm; SL 1.12 (1.05) mm; WL 2.63 (2.51) mm; DML 1.96 (1.85) mm; MW 1.43 (1.35) mm; MFL 1 .70 (1.63) mm; PH 1.15 (1.12) mm; PTL 1.13 (1.11) mm; PTW 1.06 (0.97) mm; A3L 1.21 (1.27) mm; A3W 1.43 (1.37) mm; CI 96 (95); SI 72 (70); EI 21 (22); EPI 17 (16); OI 3 (3); DMI 73 (73); DMI2 74 (74); LMI 59 (60); MFI 109 (109); PTI 94 (87); A3I 119 (107).

Body black; antennae, anterior part of cranium, mandibles, and legs reddish brown. Body pilosity relatively sparse.

Cranium in full-face view subtrapezoidal, wider posteriorly than anteriorly, faintly longer than wide (CI, 95–96); posterior part of cranium above eyes relatively short (EPI, 16–17), with PEHL much shorter than EL. Median ocellus located close to level of posteromost points of eyes in full-face view. Torulo-posttorular complex in full-face view relatively broad and partially concealing antennal socket; width, when measured at level of antennal socket, distinctly greater than length of major axis of antennal socket; lateral margin almost straight but slightly undulate, s lightly con-verging posteriad; anterior protrusion of anterolateral lobe encircling antennal socket weak, not distinctly protruding beyond anterior margin of lateral portion of clypeus in full-f ace view. Median portion of anterior clypeal margin weakly convex in full-face view, protruding beyond anterior margin of lateral portion of clypeus. Antenna 12-segmented. Maxillary palp 5-segmented. Labial palp 3-segmented. Mandible elongate, with relatively acute apex; masticatory margin feebly dentate, in dorsal view longer than twice as long as basal margin; ventral face of mandible with a series of modified seta e along masticatory margin. Mesosoma in dorsal view relatively stout (DMI, 73), with evenly rounded lateral margins. Dorsal margin of propodeal declivity in dorsal view strongly arched anteriad and margined by strong edge. Petiole in dorsal view sub trapezoidal, wider posteriorly than anteriorly, with strongly conv ex later al margin. Anterodorsal corner of abdominal tergite III forming sharp edge. Anteroventral corner of abdominal sternite III (prora) in lateral view strongly angulate with acute apex directed ventrad. Posterior margin of pygidium in dorsal view weakly concave medially.

Costae on body smoothly running, without overlaying microsculpture. Frons and vertex transversely costate. Posterolateral face of cranium and posterior face above preoccipital carina longitudinally costate. Torulo-posttorular complex and clypeus largely smooth. Gena largely smooth on face inside parafrontal ridge, whereas weakly coarsely rugose on face outside the ridge. Outer face of antenna l scape longitudinally rugulate-striate on about basiposterior diagonal half, whereas smooth on remaining face. Outer face of mandible smooth.

Promesonotum, dorsal and lateral face of propodeum longitudinally costate. Mesopleuron with oblique-longitudinal costae which run parallelly with anteroventral margin of mesopleuron. Metapleuron partly costate weakly and longitudinally. Posterior declivity of propodeum smooth. Legs largely smooth, with each coxa partly shagreened. Anterior face of petiole smooth; dorsal and lateral faces of petiolar tergite longitudinally costate. Posterodorsal face of helcium imbricate, without any costae. Costae on abdominal tergite III with costae which are transversely arched around center of posterior margin in dorsal view. Abdominal sternite III longitudinally costate. Pretergite and presternite of abdominal segment IV transversely striate (but partly imbricate). Cinctus of abdominal segment IV (boundary between pre- and postsclerites) smooth without any costae. Abdominal posttergite and poststernite IV smooth, with sparse hair-bearing foveae. Abdominal tergites and sternites V –VI imbricate on anterior marginal areas, whereas smooth, with relatively dense hair-bearing foveae on remaining face. Pygidium and hypopygium imbricate on anterior marginal area, whereas smooth submedially with dense hair-bearing foveae on remaining face.

Male
Paratype males (n=3). HL 1.31–1.33 mm; HW 1.29–1.32 mm; EL 0.47 –0.50 mm; EW 0.34 –0.38 mm; ES 0.41–0.44 mm; PEHL 0.36–0.37 mm; OL 0.12–0.13 mm; SL 0.54–0.57 mm; WL 2.67–2.80 mm; DML 2.32–2.38 mm; MW 1.70 –1.76 mm; MSL 1.09–1.14 mm; MSW 1.30–1.35 mm; MFL 1.50–1.55 mm; PTL 0.91–0.96 mm; PTW 0.82–0.87 mm; A3L 1.06–1.12 mm; A3W 1.20–1.26 mm; CI 98–99; SI 42–44; EI 32 –33; EPI 27–28; OI 10; DMI 73–74; DMI2 85–87; MSI 118 –119; MFI 117–119; PTI 88 –90; A3I 113–114.

Body black; antennae, mandibles, and legs dark reddish brown. Body pilosity relatively dense. Cranium in full-face view bulb-shaped, just faintly longer than wide (CI, 98–99); posterolateral corner somewhat angulate; vertex not strongly raised, without concealing dorsal edge of preoccipital collar in full-face view. Eye and ocelli relatively small (EI, 32–33; OI, 10); median ocellus located close to level of posteromost points of eyes in full-face view. Torulo-posttorular complex in full-face view relatively broad, partially concealing antennal socket; width, when measured at level of antennal socket, distinctly greater than length of major axis of antennal socket; lateral margin parallel in short anterior part, but l in early converging posteriorly; anterior protrusion of anterolateral lobe encircling antennal socket weak. Anterior clypeal margin in full-face view strongly convex. Antenna 13-segmented. Maxillary palp 5-segmented. Labia l palp 3-segmented. Mandible elongate, with relatively acute apex; masticatory margin feebly dentate, in dorsal view about twice as long as basal margin; ventral face of mandible with a series of modified setae along masticatory margin. Mesoscutum subpentagonal, a little wider than long (MSI, 118–119), with faintly convex anterolateral margin; notaulus completely absent; parapsidal line present as very weak and thin furrow. Scutoscutellar suture fairly deep and broad, strongly scrobiculate. Posterior margin of mesoscutellum in dorsal view strongly convex. Dorsal margin of propodeal declivity in dorsal view broadly and shallowly arched anteriad, and forming strong edge. Wing venation as generic redescription in Borowiec (2016). Petiole in dorsal view subtrapezoidal, wider posteriorly than anteriorly, with weakly convex lateral margin. Dorsal outline of abdominal tergite III in lateral view strongly rounded convex, without anterodorsal angle. Anteroventral corner of abdominal sternite III (prora) in lateral view strongly produced, with acute apex directed ventrad.

Frons weakly transversely costate. Vertex, lateral and posterior face of cranium coarsely reticulate. Torulo-posttorular complex and clypeus largely smooth. Outer face of antennal scape largely longitudinally rugulate-striate, with smooth apical face. Outer face of mandible smooth. Pronotum coarsely reticulate on dorsal face, whereas weakly and coarsely longitudinally rugose on lateral face. Mesopleuron, metapleuron, and lateral face of propodeum coarsely and irregularly rugoso-reticulate. Mesoscutum coarsely foveolate-reticulate. Mesoscutellum coarsely reticulate. Dorsum of propodeum longitudinally costate. Posterior declivity of propodeum smooth. Legs largely smooth, with meso- and metacoxae partly coarsely shagreened. Anterior face of petiole smooth; dorsal and lateral faces of petiolar tergite coarsely rugoso-reticulate. Posterodorsal face of helcium imbricate, without any costae. Abdominal tergite and sternites III largely weakly coarsely rugoso-reticulate. Pretergite and presternite of abdominal segment IV transversely striate (but partly imbricate). Cinctus of abdominal segment IV (the boundary between pre- and postsclerites) smooth, without any costae. Abdominal posttergite and poststernite IV smooth, with sparse hair--bearing foveae. Abdominal tergites and sternites V–VII imbricate on anterior marginal areas, whereas smooth with dense hair-bearing foveae on remaining face. Pygidium with dense hair-bearing foveae.

Spiculum (anterior apophysis) of abdominal sternite IX 0.30–0.31 times as long as entire length of sternite IX when spiculum length measured from transverse line spanning posteromost points of each anterolateral margin; outer margin of posterior spine of sternite IX in ventral view weakly concave; posteromedian flange between bases of posterior spines narrow, with some large irregular foveae along anteroventral margin of flange. Posterodorsal part of basimere in lateral view weakly broadly produced; articulation of basimere to teromere have thickened mar gin followed by membranous articulation. Telomere in lateral view subtriangular, 1.1–1.3 times as long as wide. Cuspis absent. Digitus in lateral view claw-shaped, entirely hooked ventrad with relatively acute apex. Posterior apex of valviceps in lateral view strongly hooked ventrad, with large acute apical denticle; posterior half of ventral margin having 10–12 broad denticles (including apical denticle); anteroventral part of valviceps reduced, in lateral view concealed by lateral apodeme.

Type Material
HOLOTYPE: Worker, Tasek Merimbun, Tutong, Brunei, K. Eguchi leg., 17.viii.1999, colony: Eg99-BOR-590 (MBD). PARATYPES: 1 Worker, 3 Males. Males from the same colony as the holotype (MBD; MHNG).

Etymology
This species is named after the type locality, Tasek Merimbun (Brunei, Tutong), adjective.

Determination Clarifications
A worker and a male of Chrysapace merimbunensis from the same colony as the type series, whose images are provided in Antweb, were once misidentified as Chrysapace sauteri. (CASENT0179562; CASENT0179567)

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.