Rhopalomastix parva 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 : 145-149

Rhopalomastix parva Wang & Jaitrong sp. nov.

urn:lsid:zoobank.org:act:AD667B83-8206-429E-8918-C8530BBC46A9

Figs 2e , 11 (worker), 12 (queen), 16a

Diagnosis

Worker

Generally small in size (TL 1.85–2.25), workers monomorphic with little to moderate intranidal size variation. Head in full-face view subrectangular, distinctly longer than wide ( Fig. 11a ); clypeus in profile strongly projected forward with short downward-sloping and weakly convex dorsal face rounding into steeper anterior face at indistinct edge, outline of anterior face broadly and weakly concave or sometimes almost flat ( Fig. 11c ). In lateral view, mesosoma elongate subcylindrical; propodeum subtrapezoidal, distinctly longer ventrally than dorsally ( Fig. 11d ). In dorsal view, anterior margin of pronotal disc strongly convex, roundly angulate at its median point, humeral corners rounded and obtusely angulate; lateral mesosomal margin weakly inflexed just before propodeum; posterolateral corners of propodeum rounded and indistinct, posterior propodeal margin weakly concave and indistinct ( Fig. 11b ). Posterior face of propodeum very weakly marginate. Petiole suboval in dorsal view, wider than long; postpetiole suboblong, about twice as wide as long ( Fig. 11b ). Dorsum and lateral face of head finely striate and shiny with scattered punctures, frons and vertex more weakly shining than rest of head dorsum. Median clypeal face mostly finely striate and shiny, with smooth and shining median longitudinal strip. Gaster largely smooth and shining, bases of gastral tergites with feeble superficial reticulation. Head and antennal funiculus mostly with dense short standing and decumbent hairs. Body mostly light brown with head and gaster darker brown; ventral faces of femora and tibiae usually pale yellowish brown.

Queen

Small size (TL 2.44–2.52). Head in full-face view subrectangular and distinctly longer than wide (CI 84– 87) ( Fig. 12a ). Lateral and ventral faces of head roughly differentiated by very weak, indistinct ridge behind eye connecting ventral margin of eye to posterolateral corner of head ( Fig. 12d ); posterolateral corner of head weakly present as bluntly rounded shallow protrusion next to posterior margin in lateral view. Ocelli small and oval, lateral ocelli closer to each other than to median ocellus ( Fig. 12a–b ). Propodeal junction indistinct, dorsum of propodeum rounding smoothly into steep, weakly convex posterior propodeal face at indistinct edge ( Fig. 12d ). In dorsal view, mesosoma subovate and distinctly narrowed posteriorly ( Fig. 12b–c ). In lateral view, petiolar node sub-trapezoidal, apical dorsum short and weakly convex, rounding into and not distinctly differentiated from posterior face ( Fig. 12d ). Posterior half of head dorsum mostly with weak striae that are more fragmented closer to posterior margin, interspaces smooth and shining; frons and vertexal area around ocelli consistently finely striate and shiny. Dorsum of mesosoma mostly finely striate and shiny, median section of pronotal dorsum smooth and shining with sparse punctures ( Fig. 12c ). Posteromedian subtriangular area of propodeal dorsum entirely smooth and shining, continuous with posterior face of propodeum that is also smooth and shining ( Fig. 12c ). Apices of petiole and postpetiole, gaster entirely smooth and shining. Dorsum of head, lateral and ventral faces with fairly dense short suberect hairs, interspersed with very sparse long erect hairs. Head, most of mesosoma, and gaster dark blackish brown; pronotum lighter greyish brown.

Etymology

The species name means ‘smallʼ in Latin, in reference to the relatively small size of this species.

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.; 18 Nov. 2019; W. Wang & W. Jaitrong leg.; hill evergreen forest, nest in bark of large dipterocarp tree, Toona ciliata M. Roem .; colony code: WJW-THL19-006; THNHM-I-21759 .

Paratypes THAILAND • 20 workers, 2 queens; same collection data as for holotype; THNHM-I-21760 to THNHM-I-21779 (20 w), THNHM-I-21780, THNHM-I-21781 (2 q) • 22 workers, 3 queens; same collection data as for holotype; GenBank: MW267129 , MW267130 (2 workers barcoded); ZRC_ ENT00013948.1 to ZRC_ENT00013948.25 .

Other material

THAILAND • 16 workers, 2 queens; Central Thailand, Nakhon Nayok Province, Muaeng District, Ban Hin Tang Subdistrict ; 14°25′53″ N, 101°22′15″ E; 800 m a.s.l.; 18 Nov. 2019; W. Wang leg.; nest in bark of large dipterocarp tree; colony code: WW-KY19-001; THNHM • 10 workers, 2 queens; same collection data as for preceding; ZRC_ENT00013951 • 8 workers; same collection data as for preceding; W. Wang & W. Jaitrong leg.; nest in bark of large dipterocarp tree, Toona ciliata ; colony code: WJW- THL19-004; THNHM • 8 workers; same collection data as for preceding; ZRC_ENT00013950 .

Description

Worker

Measurements. Holotype worker: EL 0.08; EW 0.05; HL 0.47; HW 0.41; ML 0.58; PronW 0.30 PtH 0.18; PtL 0.20; SL 0.18; TL 1.97; CI 87; PtHI 90; REL 20; SI 44.

Paratype workers (n = 8): EL 0.07–0.10; EW 0.05–0.06; HL 0.45–0.50; HW 0.38–0.42; ML 0.54–0.62; PronW 0.26–0.30; PtH 0.16–0.20; PtL 0.17–0.22; SL 0.18–0.20; TL 1.85–2.25; CI 84–87; PtHI 86–91; REL 19–24; SI 44–48.

Workers monomorphic with little to moderate intranidal variation in size. Head in full-face view subrectangular, distinctly longer than wide, posterior margin with a broad but shallow median concavity, posterolateral corners roundly angulate, lateral margins of head broadly and weakly convex, almost parallel and weakly converging anteriorly, anterior clypeal margin slightly less wide than posterior margin of head, with broadly and weakly convex median section ( Fig. 11a ). Eye with 11–15 ommatidia. In lateral view, clypeus strongly projected forward with short downward-sloping and weakly convex dorsal face rounding into steeper anterior face at indistinct edge, outline of anterior face broadly and weakly concave or sometimes almost flat ( Fig. 11c ). In lateral view, mesosoma elongate subcylindrical, dorsal outline weakly and broadly convex, propodeal junction roundly obtuse, propodeal declivity shallowly concave, propodeum subtrapezoidal, distinctly longer ventrally than dorsally ( Fig. 11d ); dorsum of propodeum differentiated from posterior declivitous face by indistinct rounded edge. In dorsal view, mesosoma subcylindrical, anterior margin of pronotal disc strongly convex, roundly angulate at its median point, humeral corners rounded and obtusely angulate; lateral margins broadly and weakly convex in anterior ¾, almost parallel to each other, weakly inflexed just before propodeum; lateral margins of propodeum broadly and more strongly convex than anterior ¾ of lateral mesosomal margin, posterolateral corners rounded and indistinct, posterior propodeal margin weakly concave and indistinct ( Fig. 11b ). Posterior face of propodeum very weakly marginate, differentiated from lateral propodeal face by indistinct rounded edge. In lateral view, petiole inclined posteriorly, slightly longer than high, distinctly narrower at apex than at base, anterior face weakly concave and longer than posterior face; apex roundly convex, apical dorsum rounding smoothly into steep posterior face at indistinct rounded edge; petiole higher and longer than postpetiole, dorsal margin of postpetiole evenly convex ( Fig. 11d ). In dorsal view, petiole suboval, wider than long; postpetiole suboblong, about twice as wide as long ( Fig. 11b ).

Dorsum and lateral face of head finely and densely striate and shiny with scattered punctures, frons and vertex more weakly shining than rest of head dorsum. Ventral face of posterior half of head mostly superficially substriate-reticulate with interspaces smooth and shining. Mandible mostly smooth and shining, area immediately adjacent to masticatory margin rugulose-punctate ( Fig. 2e ). Median clypeal face mostly finely striate and shiny, with smooth and shining median longitudinal strip. Lateral face of mesosoma largely superficially substriate-reticulate with interspaces smooth and shining ( Fig. 11d ); dorsum of mesosoma finely striate and less shiny than lateral mesosomal face ( Fig. 11b ). Lateral face of petiole superficially reticulate with interspaces smooth and shining ( Fig. 11d ), petiolar apex finely but weakly striate and shiny ( Fig. 11b ). Postpetiole largely superficially striate-reticulate with interspaces and dorsomedian spot smooth and shining. Gaster largely smooth and shining, bases of gastral tergites with feeble superficial reticulation.

Dorsum of head with fairly dense though well-spaced short erect and suberect hairs; gena and ventral face of head with fairly dense standing and short subdecumbent hairs; temple just above antennal scrobe, subocular region shortly posterior to eye, frontal carina, and median clypeal face each with a long erect hair. Antennal funiculus with dense standing and decumbent hairs. Mesosoma dorsum largely with sparse, scattered short erect hairs, posterolateral corners of propodeal dorsum with relatively denser standing hairs; dorsolateral margin lined with short standing hairs; paired long erect hairs sparsely present along dorsolateral margin, with one pair each flanking the anterior margin of pronotal disc, pronotum, mesonotum and propodeum respectively. Anterior rising face of petiole with uniformly short standing and decumbent hairs, apex and posterior declivity with dense short standing hairs, apex with one pair of long erect hairs. Postpetiole with dense short erect and suberect hairs, and one pair of long erect hairs. Gaster pilose, with dense suberect and erect hairs that are generally longer and less fine than hairs on mesosoma dorsum.

Body mostly light brown with head and gaster darker brown; tips of antennae, first funicular segment, tarsi, ventral faces of femora and tibiae pale yellowish brown.

Queen

Measurements. Paratypes, dealate queens (n = 2): EL 0.14; EW 0.10–0.11; HL 0.46–0.50; HW 0.40– 0.42; ML 0.72–0.80; MsW 0.36–0.40; PtH 0.19–0.21; PtL 0.23–0.24; SL 0.18–0.20; TL 2.44–2.52; CI 84–87; PtHI 83–85; REL 33–35; SI 45–48.

Small size (TL 2.44–2.52). Head in full-face view subrectangular, distinctly longer than wide, slightly narrower anteriorly; lateral margins broadly and weakly convex, almost entirely parallel to each other; posterolateral corners rounded, posterior margin nearly straight with a shallow median concavity ( Fig. 12a ). Eye very large (13–15 ommatidia in the longest axis); posteriormost point of eye located slightly below transverse midline of head in full-face view ( Fig. 12a ). In lateral view, clypeus weakly and broadly convex; head behind eye with very weak, indistinct ridge connecting ventral margin of eye to posterolateral corner of head, roughly differentiating lateral and ventral faces of head ( Fig. 12d ); posterolateral corner of head weakly present as bluntly rounded shallow protrusion next to posterior margin. Ocelli small and oval, median ocellus slightly larger than lateral ocelli, lateral ocelli slightly closer to each other than to median ocellus ( Fig. 12a–b ); small area immediately anterior to median ocellus weakly depressed. In lateral view, mesosoma subcylindrical, dorsal outline weakly and broadly convex, propodeal junction indistinct ( Fig. 12d ); dorsum of propodeum rounding smoothly into steep, weakly convex posterior propodeal face at indistinct edge. In dorsal view, mesosoma subobovate, distinctly narrowed posteriorly; anterior margin of pronotal disc broadly convex, humeral corners obtusely angulate, mesoscutum wider than long; propodeum much wider than long, posterior margin weakly present and indistinct, lateral propodeal margin broadly convex, rounding into posterior margin at indistinct rounded edge ( Fig. 12b ). In lateral view, petiole inclined posteriorly, longer than high, anterior petiolar face weakly concave and steep; petiolar node subtrapezoidal, apical dorsum short and weakly convex, rounding into and not distinctly differentiated from weakly convex posterior face; posterior face shorter and steeper than anterior face ( Fig. 12d ). In lateral view, postpetiole not as long as petiole, dorsal margin broadly and weakly convex ( Fig. 12d ). In dorsal view, petiole suboval, less than twice as wide as long; postpetiole globular, less than twice as wide as long.

Anterior half of head dorsum finely striate and shiny, posterior half mostly with weaker striae that are more fragmented closer to posterior margin, interspaces smooth and shining; frons and vertexal area around ocelli consistently finely striate and shiny. Clypeus mostly finely striate and shiny, with a distinct median longitudinal strip that is smooth and shining. Lateral and ventral faces of head mostly smooth and shining. Mandible mostly smooth and shining, area next to masticatory margin densely striatepunctate. Lateral face of mesosoma mostly weakly substriate-reticulate with interspaces smooth and shining; anepisternum smooth and shining with sparse fragmented striae. Dorsum of mesosoma mostly finely striate and shiny, median section of pronotal dorsum smooth and shining with sparse punctures; lateral-most triangular area of mesoscutum immediately above parascutellar carina more superficially striate than rest of mesoscutum, with smooth and shining interspaces; posteromedian subtriangular area of propodeal dorsum entirely smooth and shining, continuous with posterior face of propodeum that is also smooth and shining ( Fig. 12c ). Lateral faces of petiole and postpetiole superficially reticulate with interspaces smooth and shining ( Fig. 12d ), apicodorsal faces almost entirely smooth and shining with sparse punctures. Gaster largely smooth and shining.

Dorsum of head, lateral and ventral faces with fairly dense short suberect hairs, interspersed with very sparse long erect hairs, including one pair on median section of clypeus. Antennal scape with uniform short standing hairs and a long erect hair on basal and median points respectively. Dorsum of mesosoma with sparse short standing or decumbent hairs, more dense closer to dorsolateral margin ( Fig. 12c– d ); paired long erect hairs sparsely present along dorsolateral margin, with one pair each flanking the anterior margin of pronotal disc, pronotum, mesoscutum, and propodeum; mesoscutum and mesoscutal disc each one pair of long erect hairs. Petiole entirely with dense short standing hairs, apex with one pair of long erect hairs. Postpetiole with dense short standing hairs and 1–2 pairs of long erect hairs. Gaster pilose, with dense short standing hairs, mostly longer than those on head and mesosoma, interspersed with long erect hairs sparsely distributed along posterior margins of gastral tergites.

Head, most of mesosoma, and gaster dark blackish brown; antennal scape, pronotum, femora, petiole and postpetiole lighter greyish brown. Tips of antennae, tarsi and joints of legs pale yellowish brown.

Distribution and binomics

Thailand ( Fig. 16a ). Colonies of this species may be found in bark of Toona ciliata near edges of generally good secondary forest, at moderately high elevation (800–927 m).

Figures

Fig. 2. Closeups of external mandibular surface for workers of 5 Thai species of Rhopalomastix Forel, 1900 (ZRC); white arrows indicate distinct striations on the external mandibular face. a. R. impithuksai Wang & Jaitrong sp. nov., paratype (ZRC_ENT00007608). b. R. robusta Wang & Jaitrong sp. nov., paratype (ZRC_ENT00013949). c. R. javana Wheeler, 1929, non-type (ZRC_ENT00000932). d. R. johorensis Wheeler, 1929, non-type (ZRC_ENT00007874). e. R. parva Wang & Jaitrong sp. nov., paratype (ZRC_ENT00013948).

Fig. 11. Rhopalomastix parvaWang & Jaitrong sp. nov., paratype, worker (ZRC_ENT00013948). a. Head in full-face view. b. Body in dorsal view. c. Close-up of clypeus in profile. d. Body in lateral view.

Fig. 12. Rhopalomastix parva Wang & Jaitrong sp. nov., paratype, queen (ZRC_ENT00013948). a. Head in full-face view. b. Body in dorsal view. c. Close-up of mesosoma in dorsal view. d. Body in lateral view.

Fig. 16. Distribution maps of species of Rhopalomastix Forel, 1900 in Thailand. a. New species: R. impithuksai Wang & Jaitrong sp. nov., R. parva Wang & Jaitrong sp. nov., R. robusta Wang & Jaitrong sp. nov. b. R. javana Wheeler, 1929 and R. johorensis Wheeler, 1929.