Rhopalomastix striata

This species can be found mainly nesting in bark of large native trees, located in either primary or secondary native-dominated forest. A colony usually occupies a large expanse of the tree trunk, with numerous workers. Queens appear to be rare.

Identification
Wang, Yong, and Jaitrong (2018) - Worker. Generally monomorphic with broad size variation, relatively large size (HL 0.45– 0.54 mm; HW 0.42–0.50 mm). Head sub-rectangular in full face view, distinctly longer than wide; in profile clypeus projected slightly forward from dorsal margin of head, roundly and evenly convex; dorsum and lateral surfaces of head with dense striations; ventral head surface mostly reticulate with smooth and shining interspaces; anterior pronotal margin strongly convex and angulate at its median point in both small and large workers, outer face of femora superficially reticulate with smooth and shiny interspaces; in profile, petiole sub-trapezoidal, its anterior margin steep and nearly straight. Head and dorsum of mesosoma darker brown than rest of lighter yellowish-brown body; legs and antennae paler yellowish-brown in some workers. Small workers with generally lighter body colours.

Queen. Medium size (HL 0.54–0.55, HW 0.46). Head more rectangular than worker. In profile view, clypeus broadly and evenly convex; posterior half and ventral surface of head largely smooth and shiny, frons and vertex with feeble striations; lateral surface of pronotum, outer surface of femora and gaster superficially reticulate and shining; dorsum of mesosoma finely striate and shiny; anterior pronotal margin strongly convex and angulate at median point; humeral corners angulate; pronotum about as wide as propodeum in dorsal view; posterior face of propodeum shallowly concave, in posterior view, lateral sides of propodeum strongly concave; anterior face of petiole steep and almost straight, petiole subtrapezoidal Head, dorsum of mesosoma and gaster dark blackish brown, rest of body slightly lighter in tone, lateral surfaces of petiole, pronotum, and metapleuron more yellowish brown.

Male. Relatively large size (HL 0.45–0.47, HW 0.4–0.42). Head in full face view sub-oval; clypeus in profile strongly and evenly convex, rugulose-punctate and weakly shining; petiole subtrapezoidal, apex broadly and smoothly convex; anteroventral extension of subpetiolar process greatly reduced and small; dorsal outline of postpetiole broadly and weakly convex. Head mostly substriate-reticulate, interspaces smooth and shining, dorsum punctate; mesoscutum striated and shiny, with deep punctures. Entire body including head generally uniform blackish-brown, antennae and tips of legs pale yellowish-brown.

Workers are morphologically similar to Rhopalomastix johorensis but can be differentiated by the following characters: for small workers -1) anterior pronotal margin strongly convex, median point almost angulate, whereas in R. johorensis, anterior pronotal margin weakly and broadly convex, median point not angulate, 2) head in full face view distinctly longer than wide for both small and large workers, whereas in R. johorensis, head in full face view more squarish, almost as wide as long, especially for smaller workers, 3) in profile, outline of median clypeal projection weakly and evenly convex, projecting forward from dorsal margin of head, in R. johorensis, clypeal outline generally flat and not evenly convex, 4) posterior margin of subpetiolar process almost straight or slightly concave in profile, for R. johorensis, posterior margin of subpetiolar process often weakly convex.

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

Nomenclature

 *  striata. Rhopalomastix striata Wang, Yong & Jaitrong, 2018: 327, figs. 52-63 (w.q.m.) SINGAPORE.

Worker
Holotype: TL 2.23; HL 0.54; HW 0.48; SL 0.2; ML 0.66; PronW 0.34; EL 0.1; EW 0.07; CI 88.89; REL 20.83; SI 41.67. Four paratype workers and 7 non-types (n=11): TL 1.86–2.38; HL 0.45–0.54; HW 0.42–0.50; SL 0.16–0.22; ML 0.52–0.70; PronW 0.28–0.35; EL 0.07–0.10; EW 0.05–0.06; CI 87–93; REL 17–21; SI 38–47.

Monomorphic with broad variation in size. Head in full face view subrectangular, distinctly longer than wide, posterolateral corners smooth and rounded, lateral margins broadly and weakly convex, almost parallel to each other, posterior margin with a shallow median depression, lateral margins broadly and weakly convex. Eye relatively small, larger worker with 12–15 ommatidia, smaller worker with 10–11 ommatidia. In absolute profile, clypeus projecting forward from dorsal margin of head, roundly and evenly convex. Mesosoma in profile box-shaped, dorsal outline weakly convex; dorsolateral corner of propodeum roundly convex; metapleuron demarcated from lateral face of pronotum and metapleuron by distinct sutures. In dorsal view, mesosoma subrectangular, anterior pronotal margin strongly convex and angulate at its median point, humeral angles obtuse but smooth and rounded, lateral margins almost entirely parallel with each other, posterior margin of propodeum feebly concave or nearly straight, four corners including prontoal humeri rounded and smooth. In profile, petiole slightly inclined posteriorly, its anterior margin steep and nearly straight, higher than broad, petiolar node sub-trapezoidal, apex weakly convex, posterior declivity of petiole short. Petiole slightly higher than postpetiole; dorsal margin of postpetiole weakly convex; subpetiolar process with subtriangular anteroventral extension; posterior margin of subpetiolar process almost entirely straight or weakly concave. In dorsal view, petiole oval in shape, broader than long; postpetiole globular and larger than petiole.

Dorsal and lateral surfaces of head striated and shining. Median clypeal surface carinate with punctured interspaces and weakly shining; mandible mostly smooth and shining with few feeble striations, area close to masticatory margin with dense punctures; ventral surface of head mostly reticulate with smooth and shiny interspaces. Lateral surfaces of mesosoma weakly substriate-reticulate and shining; dorsal surface densely striated and shining. Outer face of femora superficially reticulate with smooth and shiny interspaces. Lateral surfaces of petiole and postpetiole including subpetiolar process reticulate, interspaces shining; dorsal surfaces of petiole and postpetiole striated and shining. Gaster superficially reticulate and weakly shining.

Dorsal surface of head with abundant short erect and suberect hairs, interspersed by sparse longer erect hairs. Ventral surface with numerous short appressed and decumbent hairs, ventrolateral area directly below eye with dense patch of short standing hairs, visibly more pilose than sparse hairs in adjacent genal region. Mesosoma less pilose than head, with scattered short erect and suberect hairs, sparse longer erect hairs, mostly aligned close to dorsolateral and anterodorsal sides. Petiole and postpetiole relatively more pilose, dorsal surfaces of both covered with abundant short erect and suberect hairs, generally longer than most hairs on head dorsum, each with a pair of longer erect hairs. Anterior rising face and posterior declivity of petiole also covered with dense short standing and decumbent hairs. Gaster very pilose, dorsal surface with abundant and dense erect and suberect hairs, ventral surface with thick layer of appressed and decumbent hairs.

In larger workers, head and dorsum of mesosoma dark brown, rest of body lighter in colour and roughly uniform yellowish-brown; legs and antennae may be paler yellowish light brown in some workers. For smaller workers, tonal patterns identical to larger workers, i.e. head and mesosomal dorsum darker than rest of body, but overall body colours lighter compared to large workers.

Queen
non-types (n = 2): TL 2.59–2.62; HL 0.54–0.55; HW 0.46; SL 0.2–0.22; ML 0.82–0.86; MsW 0.42–0.43; EL 0.16–0.17; EW 0.1–0.11; CI 84–85; REL 35–37; SI 43–48.

Medium size, not much larger than large worker. Head in full face view subrectangular, more rectangular than that of worker; lateral margins broadly convex and nearly parallel to each other, posterolateral corners smooth and rounded, posterior margin of head distinctly wider than anterior clypeal margin, with a shallow median concavity. Posterior margin of eye located approximately at transverse midline of head in full face view. In profile, clypeus broadly and evenly convex. Scape slightly exceeding transverse midline of head when lain back. In profile, mesosoma subcylindrical, more elongate than that of worker, dorsal outline broadly and weakly convex; posterior face of propodeum steep and shallowly concave; in posterior view, posterolateral sides of propodeum strongly concave; oblique mesopleural sulcus distinct. In dorsal view, mesosoma sub-elliptical, anterior pronotal margin strongly convex and angulate at median point; humeral corners angulate; pronotum about as wide as propodeum, clearly narrower than mesoscutum; mesoscutum about as wide as long. In profile view, petiole slightly inclined posteriorly, almost as high as long, anterior margin steep and weakly concave; petiolar node subtrapezoidal, apex rounded and blunt, slightly higher than postpetiole. In dorsal view, petiole globular, less than twice as wide as long, postpetiole also globular, much larger and wider than petiole.

Posterior half of head mostly smooth and shining, except for feeble striations and scattered punctures on frons and venter; anterior half of head largely striate-reticulate and shiny; ventral head surface mostly smooth and shining. Mandible mostly smooth and shining, area close to masticatory margin with dense punctures and weakly shining. Lateral surface of mesosoma including pronotum substriate-reticulate, interspaces smooth and shining; dorsal surface mostly striated, interspaces punctate but still shining, pronotum with weak striations, its median section almost entirely smooth and shining. Lateral surfaces of petiole and postpetiole reticulate, interspaces smooth and shining, dorsal surfaces superficially reticulate and mostly smooth and shining. Gaster largely smooth and shining, base of first tergite superficially reticulate. Dorsum of head with abundant short standing hairs of roughly uniform length, and sparse longer erect hairs; antennal scape lined with short erect hairs of roughly uniform height, and at least one longer erect hair; standing hairs on gena short and sparse. Ventral surface of head with abundant erect and suberect short hairs.

Dorsum of mesosoma with sparse pilosity, sparse short standing hairs scattered mainly on the mesoscutum and along dorsolateral margin; sparse long erect hairs along dorsolateral margin, two pairs on anterior pronotal margin. Petiole pilose, anterior face with dense, short decumbent hairs, apex and posterior declining face with abundant short standing hairs, a pair of long erect hairs on apex. Dorsal surface of postpetiole with many short suberect hairs and a pair of long erect hairs. Gaster pilose, dorsal surfaces with abundant suberect and subdecumbent short hairs, sparse long erect hairs; ventral surfaces with abundant appressed and decumbent short hairs. Pilosity denser close to distal end of gaster, around pygidium.

In general, uniformly dark blackish-brown, petiole and postpetiole lighter brown, lateral surface of petiole much paler in colour. Legs also lighter brown, colour progressively paler in tone from femur to tarsus.

Male
paratypes (n = 5): TL 2.33–2.61; HL 0.46–0.47; HW 0.4–0.42; SL 0.07–0.08; ML 0.86–92; MsW 0.46–0.54; EL 0.22–0.24; EW 0.18–0.20; CI 87–91; REL 52–60; SI 18–20.Male. Relatively large size. Head in full face view sub-oval, posterior margin roundly convex; eye just below transverse midline of head, outline of eye roundly convex and exceeding lateral margin of head. In profile, head broad-ovate and lobular, posterior margin almost straight, forming a continuous curved outline with rounded ventral margin; clypeus strongly projected from dorsal margin of head, outline strongly and roundly convex. In profile, mesosoma sub-oblong, dorsal outline very weakly convex and nearly straight, propodeal junction smooth and rounded, posterior face of propodeum short and weakly convex. In dorsal view, mesosoma obovate, narrower posteriorly, notauli absent. In profile view, petiole inclined posteriorly, subtrapezoidal and slightly longer than high, anterior margin weakly concave, apex blunt and weakly convex, posterior margin short and weakly convex; anteroventral extension of subpetiolar process greatly reduced to a very short and shallow translucent lamella. Dorsal outline of postpetiole broadly and weakly convex, separated from gaster by a weak but distinct cinctus.

Head surfaces mostly substriate-reticulate, interspaces smooth and shining, dorsum of head with scattered punctures, clypeus and its periphery more rugulose-reticulate, interspaces punctate and weakly shining. Dorsally, mesoscutum weakly and finely striated, shining and with scattered deep punctures; mesoscutal disc and dorsum of propodeum superficially reticulate, with smooth and shining interspaces; lateral surface mostly superficially reticulate with feeble substriations, interspaces smooth and shining. Petiole, postpetiole and gaster largely superficially reticulate with smooth and shining interspaces, apices of petiole and postpetiole almost completely smooth and shining.

Dorsum of head with abundant and evenly distributed short standing hairs; sparser standing hairs on lateral surface; ventral surface with abundant short appressed and decumbent hairs. Dorsum of mesosoma abundant short standing hairs, mainly concentrated on the mesoscutum. Dorsal surfaces of petiole, postpetiole with uniformly-short standing hairs. Gaster pilose, dorsum with abundant short decumbent and erect hairs roughly uniform in length, ventral surface visibly less pilose, with sparser short decumbent hairs.

Entire body including head generally uniform blackish-brown, antennae and tips of legs pale yellowish-brown. Distribution. Singapore. Etymology. The specific name refers to the fine striations on the entire dorsum and lateral head surfaces.

Type Material
Holotype. Worker, SINGAPORE, Mandai Road (1.41440°N, 103.79845°E), behind bark of Dipterocarpaceae, 18 Nov 2016, G.W. Yong & S.X. Chui leg., colony no. GY-SG16-RhoG, ZRC_ENT_00000876. Paratypes. Thirty-six workers (,, , ZRC), five males (ZRC), same data as holotype, ZRC_HYM_0000290.

Etymology
The specific name refers to the fine striations on the entire dorsum and lateral head surfaces.

References based on Global Ant Biodiversity Informatics

 * Wang W. Y., G. W. J. Yong, and W. Jaitrong. 2018. The ant genus Rhopalomastix (Hymenoptera: Formicidae: Myrmicinae) in Southeast Asia, with descriptions of four new species from Singapore based on morphology and DNA barcoding. Zootaxa 4532: 301-340.