Rhopalomastix robusta Wang & Jaitrong, 2021

Wang, Wendy Y., Yong, Gordon W. J. & Jaitrong, Weeyawat, 2021, Revision of the elusive ant genus Rhopalomastix (Hymenoptera, Formicidae, Myrmicinae) in Thailand based on morphology and DNA barcodes, with descriptions of three new species, European Journal of Taxonomy 739 (1), pp. 117-157 : 150-154

publication ID	https://doi.org/ 10.5852/ejt.2021.739.1271
publication LSID	lsid:zoobank.org:pub:81383BD5-6040-4156-BD09-A2704E5D9DA7
DOI	https://doi.org/10.5281/zenodo.4614560
persistent identifier	https://treatment.plazi.org/id/7FE9D47B-988F-40BB-9AEE-C208F52D6159
taxon LSID	lsid:zoobank.org:act:7FE9D47B-988F-40BB-9AEE-C208F52D6159
treatment provided by	Plazi
scientific name	Rhopalomastix robusta Wang & Jaitrong
status	sp. nov.

Treatment

Rhopalomastix robusta Wang & Jaitrong sp. nov.

urn:lsid:zoobank.org:act:7FE9D47B-988F-40BB-9AEE-C208F52D6159

Figs 2b View Fig , 13 View Fig (average worker), 14 (large worker), 15 (small worker), 16a

Diagnosis

Worker

Relatively large size (small worker TL> 2 mm; large worker TL> 3 mm) with robust habitus; workers monomorphic with broad intranidal size variation. Head subsquarish, as long as wide or slightly wider than long; in small workers slightly longer than wide; distinctly narrowed anteriorly; narrow median furrow between frontal lobes deep and long, extending till or past transverse midline of head, narrower or constricted shortly before midlength; posterolateral corners roundly convex and laterally expanded forming somewhat rounded vertexal lobes ( Figs 13a View Fig , 14a View Fig , 15a View Fig ). Anterior clypeal face in profile weakly and evenly convex, sometimes almost flat ( Fig. 13c View Fig ). In dorsal view, anterior margin of pronotal disc broadly convex with bluntly angulate median point, humeral corners obtusely angulate, lateral margins with distinct inflexions differentiating pronotum, mesonotum and propodeum; posterolateral corners of propodeum indistinct and rounded; posterior propodeal margin indistinctly concave ( Figs 13b View Fig , 14b View Fig , 15b View Fig ). Posterior face of propodeum very weakly marginate, rounding smoothly into lateral propodeal face without distinct marginate edge. Median clypeal face coarsely carinulate, interspaces punctate and weakly shiny. Mandible with upper half of outer face finely striate, lower half superficially substriate ( Fig. 2b View Fig ). Petiolar node and postpetiole each with two pairs of very long erect hairs. In larger workers, head, dorsum of mesosoma, and procoxa blackish or dark reddish brown, with rest of body generally uniformly lighter brown, tips of antennae and legs pale yellowish brown.

Etymology

The species name is a both a direct reference to the robust habitus of the workers, and also a subtle allusion to the species’ intense dark brown colour resembling brewed robusta coffee.

Material examined

Holotype THAILAND • worker; Central Thailand, Nakhon Nayok Province, Muaeng District, Ban Hin Subdistrict ; 14°26′14″ N, 101°22′33″ E; 927 m a.s.l.; 8 Jan. 2018; W. Jaitrong leg.; hill evergreen forest, nest in bark of Toona ciliata M. Roem. ; colony code: WJT080118-1; THNHM-I-21782 . GoogleMaps

Paratypes THAILAND • 19 workers; same collection data as for holotype; THNHM-I-21783 to THNHM-I-21801 GoogleMaps • 10 workers; same collection data as for holotype; 18 Nov. 2019; W. Wang & W. Jaitrong leg.; hill evergreen forest, nest in bark of Toona ciliata ; colony code: WJW-THL19-007; THNHM GoogleMaps • 77 workers; same collection data as for preceding; GenBank: MW267049 View Materials to MW267051 View Materials (3 barcoded); ZRC_ ENT00013949.1 to ZRC_ENT00013949.77 GoogleMaps .

Description

Worker

Measurements. Holotype worker: EL 0.12; EW 0.08; HL 0.64; HW 0.66; ML 0.86; PronW 0.46; PtH 0.25; PtL 0.27; SL 0.28; TL 2.91; CI 103; PtHI 93; REL 18; SI 42.

Paratype workers (n = 12): EL 0.09–0.14; EW 0.06–0.08; HL 0.55–0.68; HW 0.52–0.70; ML 0.68–0.96; PronW 0.36–0.48; PtH 0.19–0.28; PtL 0.20–0.31; SL 0.24–0.31; TL 2.24–3.16; CI 95–103; PtHI 91–96; REL 17–20; SI 42–46.

Relatively large sized for Rhopalomastix (TL 2.24–3.16) with habitus generally robust; workers monomorphic with broad size variation. Head in full-face view subsquarish, as long as wide or slightly wider than long (CI 100–103), in small workers sometimes slightly longer than wide ( Fig. 15a View Fig ), distinctly narrowed anteriorly; narrow median furrow between frontal lobes deep and long, extending till or past transverse midline of head, narrower or constricted shortly before midlength; posterior margin with a broad but shallow median concavity, posterolateral corners roundly convex and laterally expanded to form somewhat rounded vertexal lobes, lateral margins of head broadly convex and weakly converging anteriorly, anterior clypeal margin with broadly and weakly convex median section ( Figs 13a View Fig , 14a View Fig , 15a View Fig ). Eye with 16–20 ommatidia in small workers, 22–32 ommatidia in larger workers. In lateral view, anterior face of clypeus weakly and evenly convex, sometimes almost flat ( Fig. 13c View Fig ). Mesosoma in lateral view box-shaped and subcylindrical, dorsal outline weakly and broadly convex, almost flat, propodeal junction roundly obtuse, propodeal declivity steep and shallowly concave ( Figs 13d View Fig , 14c View Fig , 15c View Fig ); propodeal dorsum rounding smoothly into posterior declivitous face at indistinct edge. In dorsal view, mesosoma subcylindrical, anterior margin of pronotal disc broadly convex with bluntly angulate median point, humeral corners obtusely angulate, lateral margins with distinct inflexions differentiating pronotum, mesonotum and propodeum ( Figs 13b View Fig , 14b View Fig , 15b View Fig ); in large workers, mesosoma weakly narrowed posteriorly ( Fig. 14b View Fig ); lateral margins of propodeum broadly convex with indistinct rounded posterolateral corners, posterior propodeal margin weakly defined ( Figs 13b View Fig , 14b View Fig , 15b View Fig ). Posterior face of propodeum very weakly marginate and almost flat, sometimes with upper half shallowly depressed, rounding smoothly into lateral propodeal face without distinct marginate edge. In lateral view, petiole inclined posteriorly and bell-shaped, slightly longer than high, anterior face steep and weakly concave, apex rounded and slightly higher than postpetiole, apical dorsum rounding into weakly convex posterior face at indistinct rounded edge, posterior face steeper and shorter than anterior face ( Figs 13d View Fig , 14c View Fig , 15c View Fig ). Petiole higher and longer than postpetiole, dorsal margin of postpetiole weakly convex, almost flat in large workers ( Fig. 14c View Fig ). In dorsal view, petiole suboval, wider than long; postpetiole globular, less than twice as wide as petiole ( Figs 13b View Fig , 14b View Fig , 15b View Fig ).

Dorsum of head finely striate and dully shining with scattered punctures, lateral face substriate-reticulate with scattered punctures and interspaces smooth and shining; ventral face largely finely reticulate with interspaces smooth and shining; median clypeal face coarsely carinulate, interspaces punctate and weakly shiny. Mandible in full-face view with upper half of outer face finely striate, lower half superficially substriate ( Fig. 2b View Fig ), in larger workers striae on mandible more coarse, area immediately adjacent to masticatory margin punctate. Lateral face of mesosoma largely substriate-reticulate with interspaces smooth and shining ( Figs 13d View Fig , 14c View Fig , 15c View Fig ); dorsum of mesosoma finely striate and shiny ( Figs 13b View Fig , 14b View Fig , 15b View Fig ); posterior face of propodeum superficially and transversely substriate-reticulate with interspaces smooth and shining. Coxae and femora distinctly but superficially reticulate with interspaces smooth and shining. Lateral faces of petiole and postpetiole superficially substriate-reticulate with interspaces smooth and shining, apicodorsal faces largely superficially reticulate with interspaces smooth and shining, apicalmost point of petiole entirely smooth and shining. Gaster largely superficially reticulate with interspaces smooth and shining; sculpture slightly stronger around base of first gastral tergite where it articulates with postpetiole.

Dorsum and ventral face of head with fairly dense though well-spaced short standing and suberect hairs interspersed with sparse long erect hairs ( Figs 13a View Fig , 14a View Fig , 15a View Fig ); lateral face with short suberect and subdecumbent hairs. Mesosoma dorsum with scattered short standing hairs, more dense close to dorsolateral margin ( Figs 13b View Fig , 14b View Fig , 15b View Fig ); paired long erect hairs sparsely present along dorsolateral margin, with at least one pair each flanking the anterior margin of pronotal disc, pronotum, mesonotum and propodeum; large workers sometimes with 2–3 pairs of long erect hairs on anterior margin of pronotal disc, and/or 2–3 pairs of long erect hairs flanking pronotum and propodeum. Anterior rising face of petiole with relatively sparse (compared to head) short decumbent and subdecumbent hairs, slightly more dense closer to apex; lateral petiolar face with 1–2 very long erect hairs and standing hairs slightly longer than those on anterior face, mostly densely along posterolateral margin; apex of petiolar node with sparse standing hairs longer than those on anterior face, and two pairs of very long erect hairs; posterior petiolar face almost hairless or with sparse short standing hairs. Postpetiole with fairly dense erect and suberect hairs longer than those on anterior petiolar face, and two pairs of much longer erect hairs. Gaster pilose with dense erect and suberect hairs, interspersed with sparse long erect hairs.

Head and dorsum of mesosoma generally dark brown with rest of body mostly uniformly lighter brown. In larger workers, head, dorsum of mesosoma, and procoxa blackish or dark reddish brown; petiolar apex and dorsum of postpetiole generally darker brown than their respective lateral faces. Tips of antennae and legs pale yellowish-brown.

Distribution and binomics

Thailand ( Fig. 16a View Fig ). This species is thus far only known from its type series, collected from relatively good secondary forest at moderately high elevation (927 m). The colony was found in bark of a large dipterocarp tree, Toona ciliata , located near the edge of the forest. Members of the colony seemed rather gregarious when found, with numerous individuals moving quickly en masse as a collective group to seek cover when exposed upon removal of a bark layer.

Remarks

Smaller workers of R. robusta Wang & Jaitrong sp. nov. are similar to large workers of both R. impithuksai Wang & Jaitrong sp. nov. and R. johorensis . The first two species can be differentiated by the following: 1) striations on dorsum of head uniformly dense from frontal lobes to posterior margin in R. robusta Wang & Jaitrong sp. nov., but in R. impithuksai Wang & Jaitrong sp. nov., striations on head dorsum are weaker and more fragmented in posterior half; 2) outline of clypeus in lateral view–entirely flat or weakly convex with no angulate edge in R. robusta Wang & Jaitrong sp. nov., but with short weakly convex dorsal face separated from steep and almost flat anterior face by a weak angulate edge in R. impithuksai Wang & Jaitrong sp. nov.; 3) head in full-face view as long as wide or sometimes wider than long for R. robusta Wang & Jaitrong sp. nov., whereas for R. impithuksai Wang & Jaitrong sp. nov., head in fullface view always longer than wide; 4) median furrow on head dorsum starting from between frontal lobes quite long and relatively deep in R. robusta Wang & Jaitrong sp. nov., either extending till or past transverse midline of head, in R. impithuksai Wang & Jaitrong sp. nov. the median furrow is shorter, usually narrower and shallower in its posterior half, often fading out before transverse midline of head. Points (3) and (4) can also be used to distinguish between R. robusta Wang & Jaitrong sp. nov. (small workers) and R. johorensis (large workers).