KUEC; Holotype (major worker); Cambodia: Siem Reap Province, Local Forest Administration plot, 13°43'47"N, 104°02'38"E, 13. XII. 2012, S. Hosoishi leg., SH12-Cam-135 (collection code KUECANT031). – KUEC; Paratypes: 2 major workers (collection code KUECANT032, KUECANT033) (KUEC), 4 minor workers (collection code KUECANT034, KUECANT035, KUECANT036, KUECANT037) (KUEC), same data as holotype.

Three minor workers (collection code KUECANT038, KUECANT039, KUECANT040) (KUEC), same data as holotype.

Carebara colobopsis can be distinguished from the other species in the genus by the following characters: truncated head, posterolateral corner of head with a horn, 9-segmented antennae, distinct metanotum and deep metanotal groove, propodeal declivity with lamella laterally in the major worker subcaste; longer head, 9-segmented antennae, smooth surface of promesonotum, deep metanotal groove, propodeum armed with a long acute tooth, propodeal declivity with lamella and petiolar venter with lamella along its length in the minor worker subcaste.

Holotype major worker: HL 0.84; HW 0.63; SL 0.29; ML 0.22; EL 0.05; EM 0.22; HD 0.53; WL 0.68; PSL 0.13; PW 0.35; MFL 0.41; MFW 0.11; MTL 0.33; PTL 0.26; PTH 0.18; PNL 0.10; PTW 0.18; PSD 0.03; DPSD 0.06; PPL 0.15; PPNL 0.10; PPH 0.14; PPW 0.19; GL 1.06; GW 0.69; CI 75; MI 26; SI 34; MLI 49; PPLI 55; PPI 106; PSI 21. Paratype major workers (n = 2): HL 0.82–0.86; HW 0.63–0.64; SL 0.28–0.30; ML 0.20–0.21; EL 0.04–0.05; EM 0.22–0.23; HD 0.53–0.55; WL 0.71–0.72; PSL 0.13–0.14; PW 0.36–0.38; MFL 0.41–0.42; MFW 0.11–0.12; MTL 0.33–0.35; PTL 0.26–0.28; PTH 0.18–0.19; PNL 0.09–0.10; PTW 0.18–0.19; PSD 0.03–0.04; DPSD 0.06–0.07; PPL 0.14–0.15; PPNL 0.10–0.12; PPH 0.14–0.15; PPW 0.19–0.21; GL 1.00–1.39; GW 0.48–0.80; CI 73–76; MI 23–25; SI 33–35; MLI 48–50; PPLI 51–56; PPI 106–118; PSI 20–23. Paratype minor workers (n = 4): HL 0.36–0.38; HW 0.30–0.31; SL 0.23–0.24; ML 0.08–0.10; EL 0.01; EM 0.09–0.10; HD 0.21–0.22: WL 0.36–0.39; PSL 0.07–0.09; PW 0.17–0.18; MFL 0.23–0.24; MFW 0.05–0.06; MTL 0.18–0.19; PTL 0.15–0.16; PTH 0.10–0.11; PNL 0.06–0.07; PTW 0.06–0.07; PSD 0.01–0.02; DPSD 0.01–0.02; PPL 0.06–0.07; PPNL 0.06; PPH 0.06–0.07; PPW 0.08–0.09; GL 0.31–0.34; GW 0.22–0.26; CI 81–84; MI 22–26; SI 61–65; MLI 63–67; PPLI 41–46; PPI 118–139; PSI 26–28.

Head, in full-face view, nearly rectangular, long, about 1.3 times as long as wide (CI 73–76), phragmotic with truncated anterior surface of head; posterior margin medially concave; posterolateral corner rounded; lateral margin straight to weakly convex. Posterolateral corner of head with a distinct, acute tooth resembling a horn. Supraclypeal area with deep transverse concavity located just behind posterior margin of clypeus. Clypeus entirely involved in phragmotic shield, margined throughout with continuous high rim; anterior margin medially and laterally very shallowly emarginate. Head, in profile view, gradually narrowed posteriad, with straight anterior margin; dorsal and ventral margins shallowly convex; anterior portion (phragmotic shield) separated from posterior portion by right-angled bent just in front of antennal socket. Ocelli absent. Compound eyes small, consisting of five to six ommatidia (EL 0.05). Mandibles in frontal view roughly triangular, taking part in round phragmotic shield; masticatory margin straight with six low and blunt teeth; basal margin shallowly convex; outer margin evenly curved. Antenna with nine segments; scape short (HL 0.82–0.86, SL 0.28–0.30, SI 33–35) not surpassing cephalic midlength, basally narrow and widening apicad; third to seventh antennal segments short, globular; apical two segments forming distinct club.

With mesosoma in dorsal view, pronotum globular, large, occupying most of mesosoma; mesonotum small, transverse, nearly as wide as propodeum; promesonotal suture faint; metanotum forming narrow, elevated band; dorsal face of propodeum wider than long; not defined from posterior declivity with carina; both dorsal and posterior faces flanked with high lamellae. In profile view, promesonotum high and dome-like; mesopleuron weakly differentiated into upper and lower portions; lower portion anteriorly and ventrally margined with carinae; metanotum separated from mesonotum and propodeum by deep furrows. Propodeum higher than long, with dorsal outline almost flat, armed at posterior angle with an angulate tooth posterodorsally directed; posterior margin lamellate; propodeal lobe triangular. Propodeal spiracle round and situated slightly above mid-height of sclerite, and slightly posterior to mid-length of sclerite; distance from propodeal spiracle to posterodorsal corner of propodeum (PSL 0.13–0.14) about four times the diameter of spiracle (PSD 0.03–0.04), and distance to declivity (DPSD 0.06–0.07) about twice the diameter of spiracle.

Petiolar node, in dorsal view, wider than long (PTW 0.18–0.19, PNL 0.09–0.10); petiolar peduncle long, longer than wide, widened posteriad. Postpetiolar node nearly rectangular in outline, wider than long, slightly wider than petiolar node (PPW 0.19–0.21, PTW 0.18–0.19). Petiole, in profile view, longer than high (PTL 0.26–0.28, PTH 0.18–0.19) and with long peduncle; ventral outline of petiole nearly flat, anteriorly with subpetiolar process that is reduced to a small convexity; node differentiated from peduncle by rather distinct flection; node apically blunt, with posterior outline convex and with similar inclination as anterior outline. Postpetiolar node rounded and lower than petiolar node.

Dorsal surface of head (frons and vertex) finely reticulate-rugose, with interspaces closely punctate; irregular short rugulae present just behind posterior margin of cephalic shield; posterior one-fourth of head dorsum with irregular transverse rugulae especially around horns; horn with longitudinal rugulae which extend to tip; dorsolateral face of head areolate-rugose. Upper two-thirds of phragmotic shield (mainly clypeus) finely shagreened and mat, with irregularly arranged stout rugulae. In profile, lateral face of head closely and minutely punctate; posterolateral portion of cephalic dorsum finely areolate-rugose. Dorsum of mandibles (constituting lower one-third of phragmotic shield) with similar surface sculpture as in upper portion of phragmotic shield. Pronotum almost entirely smooth and shiny, with polka-dot pattern seen through transparent cuticle; narrowed anterior portion (neck) and anterolateral area closely punctate and mat to coriaceous. Mesonotum superficially punctate and rather shiny; mesopleuron generally smooth and shiny. Metanotum (elevated narrowly transverse sclerite) sparsely punctate and shiny; furrows flanking it anteriorly and posteriorly minutely punctate and mat; metapleuron entirely closely puncto-reticulate. Propodeum entirely puncto-reticulate including spines and lateral lamellae on declivity. Petiole and postpetiole closely puncto-reticulate except for posterior face of postpetiole weakly rugose and dorsal central portion of postpetiole smooth and shiny. Gaster smooth and shiny, with anterior narrowed portion striate.

Dorsal face of head with erect hairs sparsely, mixed with sparse appressed pubescence; anterior portion or cranium just behind phragmotic shield with three pairs of erect hairs (two pairs on supraclypeal area anteriorly and laterally, and one pair near antennal socket); lateral margin of head with few long hairs, and posterolateral corner of head around horn with suberect to curved hairs of various length. No visible hairs on cephalic shield. Outer margin of mandible with inconspicuous short appressed hairs; ventral face with erect or suberect hairs. Scape with appressed short hairs, without erect hairs. Promesonotum with less than ten long and fine erect hairs and sparse appressed pubescence. Propodeum often with a pair of suberect hairs. Petiole and postpetiole each with a pair of long suberect hairs and some decumbent hairs. Gaster with rather long appressed pubescence and long suberect hairs sparsely. Tibiae with decumbent hairs, without standing hairs. Body yellowish ferruginous; legs and parts of gaster, slightly lighter.

Head, in full-face view, long, about 1.2 times as long as wide (CI 81–84), weakly subrectangular and slightly narrowed anteriorly; posterior margin almost straight, posterolateral corners rounded, and lateral margins convex. Frontal lobes elongate, widened anteriad, covering antennal sockets; frontal carinae short, as long as frontal lobe, diverging posteriad, with anterior two-fifths thickened. Frontal triangle distinct, shallowly depressed. Clypeus posteriorly extends to level of anterior extremity of frontal carina, between lobes almost as wide as lobe. Median disk of clypeus with fine lateral carinae that diverge anteriad; anterior margin of clypeus widely shallowly emarginate, with roundly angulate lateral corners that are lamellate; the lamella extends entire length of lateral margin of median disk of clypeus. Eyes present, consisting of one ommatidium (EL 0.01). Mandibles with five teeth. Antennae with nine segments; scape fails to reach posterior margin of head (HL 0.36–0.38, SL 0.23–0.24, SI 61–65).

In dorsal view, pronotum large, longer than wide; main sclerite round with anterior margin nearly straight and lateral margin roundly convex; prescutum (neck) of pronotum rather wide, slightly less than two-thirds as wide as main sclerite. Mesonotum not clearly demarcated from pronotum, narrower than the latter, tapered posteriad. Metanotal groove distinct, transverse, laterally margined with carinae. Propodeal dorsum longer than wide, widened posteriad, with long spines slightly directed outwardly. In profile view, promesonotum moderately and roundly convex dorsally. Pronotum with distinctly defined prescutum. Mesopleuron clearly differentiated from pronotum and metapleuron, divided into upper and lower portions by type of sculpture; lower portion anteriorly margined with distinct lamella. Metanotal groove impressed. Propodeum not clearly demarcated from metapleuron, about 1.5 times as high as long, with distinct dorsal face declining posteriorly, spines long and acute, posterodorsally directed and ventrally equipped with lamella that continues along posterior margin of declivity; the latter portion of lamella inflated below. Propodeal lobe triangular; spiracle rounded and situated slightly above mid-height of sclerite, and close to posterior margin of propodeum; distance from propodeal spiracle to posterodorsal corner of propodeum (PSL 0.07–0.09) much longer than diameter of spiracle (PSL 0.01–0.02), and distance to declivity (DPSD 0.01–0.02) as large as diameter of spiracle.

With waist in dorsal view, petiolar node as wide as long (PTW 0.06–0.07, PNL 0.06–0.07), and postpetiolar node slightly wider than petiolar node (PPW 0.08–0.09, PTW 0.06–0.07). Postpetiole wider than long, slightly wider than petiole. In profile view, petiole longer than high (PTL 0.15–0.16, PTH 0.10–0.11) with relatively long peduncle; sternite ventrally equipped with lamella over its length and has almost straight outline. Petiolar node demarcated from anterior peduncle by distinct bent; its dorsum with flat outline, and longer than anterior slope and as long as posterior slope; posterior margin of node convex. Subpetiolar process forming a blunt denticle, its height measuring almost same as diameter of propodeal spiracle. Postpetiole much smaller and lower than petiole and globular; node weakly convex dorsally. Anterolateral corners of first gastral tergite distinctly tuberculate.

Dorsal surface of head including clypeus principally smooth, except for frontal lobe, lateral transverse area of clypeus and area between antennal socket and outer margin of head that are longitudinally rugose; anterior slope of clypeus punctate. Lateral and ventral faces of head principally smooth and shiny. Mandibles nearly smooth on dorsal face, superficially sculptured on laterobasal portion. Promesonotum smooth and shiny, except for prescutum (neck) of pronotum and posterior extremity of mesonotum puncto-reticulate. Lower portions of mesopleuron and metapleuron punctate; upper portions of mesopleuron and metapleuron smooth. Dorsal surface and posterior declivity (upper half) of propodeum densely punctate (punctures larger than those on mesopleuron); lower half of declivity smooth. Petiole and postpetiole densely punctate, except for dorsal central portion of postpetiole very weakly sculptured and shiny. Gastral tergites smooth and shiny except for presclerite of first tergite densely sculptured.

Dorsum of head with sparse appressed/decumbent short hairs and a few erect hairs; lateral margin and posterior margin of head sparsely with erect/suberect hairs. Scape with short decumbent hairs. Outer margin of mandible with decumbent hairs. Mesosoma with four pairs of erect hairs, one pair on pronotum, two pairs on mesonotum, and one pair on propodeum. Petiole and postpetiole each with two pairs of erect/suberect hairs; gaster with sparse suberect hairs. Femora and tibiae with decumbent hairs. Color yellow.

This species belongs to the C. acutispina group. In the major worker it is easily distinguished from the other Asian members of the genus by the combination of the following conditions: the anteriorly truncated head, posterolateral corner of head with a horn, 9-segmented antennae, distinct metanotal disc, deep groove in front of the disc, developed propodeal spines, and laterally lamellate propodeal declivity. Minor workers characteristically have lamellae on the venter of the petiole and on the lateral margins of the propodeal declivity (the lamella on the propodeal declivity involves propodeal spine and extends anteriad up to the anterior margin of the propodeal dorsum as a low carina), and sparse erect hairs on the body.

The type series was collected from leaf litter in a lowland dry evergreen forest (Fig. 4).

This species is only known from the type locality in Cambodia.

The species name refers to the anteriorly truncated head of the major worker subcaste.