Carebara bifida Matsuura & Hosoishi, 2025

Matsuura, Kohei, Hosoishi, Shingo & Pham, Hong Thai, 2025, Taxonomic revision of the Carebara oni species group, with descriptions of two new species from Vietnam (Hymenoptera, Formicidae, Myrmicinae), Deutsche Entomologische Zeitschrift 72 (2), pp. 377-393 : 377-393

Carebara bifida Matsuura & Hosoishi sp. nov.

Fig. 8 A – F

Type material examined.

Holotype: Vietnam • major worker; Cuc Phuong National Park , Ninh Binh Province; 20°14'N, 105°36'E; 25. Aug. 2019; S. Hosoishi leg.; dead wood; colony SH 19-Vie-73 ; VNMN, collection code KUECCRB 016 . Paratypes: Vietnam • 2 major workers and 10 minor workers; Cuc Phuong National Park , Ninh Binh Province; 20°14'N, 105°36'E; 25. Aug. 2019; S. Hosoishi leg.; dead wood; colony SH 19-Vie-73 ; KUEC, collection code KUECCRB 017 , 018, 019, 020, 021, 022, SKYC, collection code KUECCRB 023 , 024, 025, 026, 027, 028 .

Non-type material examined.

Vietnam • 1 major worker and 1 minor worker; Chua Yen Tu , Quang Ninh Province; 21°09'N, 106°43'E; 720–845 m alt.; 20. May 2019; K. Eguchi leg.; rotting part of living tree bamboo forest; colony Eg 04-VN-065 ; ACEG . 1 major worker and 1 minor worker; W. Yen Tu , Bac Giang Province; 21°10'18.1"N, 106°43'16.0"E; ca. 370 m alt.; 2. Apr. 2003; K. Eguchi leg.; colony Eg 03-VN-163 ; ACEG . 1 minor worker; Nam Xe , Van Ban District, Lao Cai Province; 620–700 m alt.; 2. Oct. 2006; K. Eguchi leg.; colony Eg 02 x 06-03 ; ACEG .

Diagnosis of worker.

Major worker: Dorsal surface of promesonotum smooth and shiny. Lateral surface of pronotum entirely smooth and shiny. Lower portion of mesopleuron punctate posteriorly, smooth and shiny anteriorly. Reticulation on dorsal surface of propodeum indistinct. Posterodorsal margin of petiolar node in profile view weakly curved. Subpetiolar process acute. Minor worker: Vertex reticulate. Lateral margin of head converging, not parallel in full-face view. Dorsal surface of pronotum smooth and shiny. Propodeal spiracles almost tangent to propodeal declivity. Lateral propodeum reticulate. Dorsal surface of petiolar node reticulate. Subpetiolar process acute.

Measurements

(in mm) and indices. Holotype (Major worker): TL 2.97, HL 0.76, HW 0.68, SL 0.40, EL 0.10, ML 0.68, MW 0.38, PSL 0.12, PSD 0.03, PL 0.35, PH 0.22, DPW 0.17, PPL 0.18, CI 90, SI 52, PI 1 159, PI 2 50. Paratype (Major worker, n = 2): TL 2.82–3.03, HL 0.74–0.75, HW 0.70–0.71, SL 0.35–0.36, EL 0.10–0.12, ML 0.73–0.77, MW 0.36–0.40, PSL 0.11–0.17, PSD 0.03–0.04, PL 0.35–0.37, PH 0.21–0.23, DPW 0.17–0.18, PPL 0.16–0.19, CI 94, SI 46–49, PI 1 162–164, PI 2 44–47. Paratype (Minor worker, n = 10): TL 1.05–1.41, HL 0.36–0.41, HW 0.34–0.38, SL 0.20–0.26, EL 0.01, ML 0.37–0.42, MW 0.21–0.23, PSL 0.06–0.08, PSD 0.02–0.03, PL 0.16–0.17, PH 0.10–0.11, DPW 0.07–0.08, PPL 0.08–0.09, CI 89–100, SI 55–63, PI 1 152–172, PI 2 44–58.

Description of worker.

Worker caste dimorphic.

Major worker. (Fig. 8 A – C ).

Head in full-face view subsquare ( CI 90–94); posterior cephalic border concave in middle; posterolateral corners rounded; lateral margins slightly convex. Anterior clypeal margin concave in middle, with a pair of blunt protrusions. Frontal carinae inconspicuous. Frontal triangle well-defined. Mandibles short, subtriangular, masticatory margins with six teeth; apical three teeth large, basal three teeth smaller. One median ocellus and two tubercles present; in other specimens, one median ocellus and two lateral ocelli present, tubercles absent. Eyes large, ten ommatidia visible, situated at anterior one-third of lateral head. Antennae with nine segments, with a two-segmented club; scapes narrower than eye, clavate, almost half of the head length ( SI 46–52); antennal segment II, VIII, and IX longer than wide, III – VII wider than long.

Mesosoma almost same size as head ( HL 0.74–0.76, ML 0.68–0.77). Promesonotum roundly convex and higher than propodeum in profile view; anterior and lateral margins of promesonotum convex in dorsal view; promesonotal suture distinct, convex forward in dorsal view. Dorsal outline of mesonotum concave in profile view; scutellum present. Metanotal groove present; metanotum present as elevated band. Dorsal outline of propodeum declining backwards; propodeal spiracle large ( PSD 0.03–0.04) and rounded, situated above mid-height of propodeum and beyond mid-length of propodeum; propodeal spine blunt, short ( PSL 0.11–0.17).

Petiole longer than high ( PI 1 159–164), with short peduncle and high node, broader posteriorly in dorsal view; ventral outline concave; subpetiolar process acute. Postpetiole higher than long, shorter than petiole, lower than petiolar node in profile view; in dorsal view, postpetiole elliptical, wider than petiolar width. Gastral tergite I larger than remaining segments.

Frons and anterior part of vertex with longitudinal irregular rugulae. Clypeus smooth and shiny medially, lateral sides longitudinally striated. Frontal triangle smooth and shiny. Frontal lobes longitudinally striated. Mandibles smooth and shiny. Pronotum, mesonotum, and scutellum smooth and shiny. Upper portion of mesopleuron smooth and shiny (in other specimens, mesopleuron reticulate); lower portion of mesopleuron reticulate posteriorly, smooth and shiny anteriorly. Metapleuron reticulate. Dorsum of propodeum weakly reticulate; lateral surface reticulate. Legs smooth and shiny. Petiole reticulate. Disc of postpetiole smooth and shiny. Gastral tergite I smooth and shiny.

Dorsum of head with abundant short decumbent and sparsely long erect hairs; vertex with short decumbent hairs. Anterior median clypeus with two pairs of long erect hairs. Mandibles, masticatory margins with long decumbent hairs; surface with short decumbent hairs. Antennal scapes with dense decumbent hairs. Mesosoma with short decumbent and long erect hairs. Legs with short decumbent hairs. Petiolar node and postpetiole with long erect hairs. Gastral tergite I with short decumbent and sparsely long erect hairs.

Head, mesosoma, waist and gaster dark brown. Antennae and legs yellowish brown.

Minor worker. (Fig. 8 D – F ).

Head in full-face view almost as wide as long, subsquare ( CI 89–100); posterior cephalic border almost straight; posterolateral corners rounded; lateral margins convex. Anterior clypeal margin concave in middle, with a pair of acute protrusions. Frontal carinae present. Frontal triangle well-defined. Mandibles short, subtriangular; masticatory margins with six teeth. Eyes with one ommatidium, situated laterally at anterior one-third of head. Antennae with nine segments, with a two-segmented club; scapes wider than eyes, clavate and longer than half of head length ( SI 55–63); antennal segment II, VIII, and IX longer than wide, III – VII wider than long.

Mesosoma almost same size as head ( HL 0.36–0.41, ML 0.37–0.42). Promesonotum roundly convex and higher than propodeum in profile view; in dorsal view, anterior margin convex forward and lateral margins converging posteriorly; promesonotal suture indistinct. Mesopleuron not separated by transverse striae. Metanotal groove present. Dorsal outline of propodeum declining backwards; propodeal spiracle large ( PSD 0.02–0.03) and rounded, situated above mid-height of propodeum, touching propodeal declivity; propodeal spines acute, short ( PSL 0.06–0.08); propodeal lamella thin in upper part, thick in lower part in profile view.

Petiole longer than high ( PI 1 152–172), with short peduncle and low node in profile view; dorsal outline between peduncle and node weakly curved in profile view; in dorsal view, broader posteriorly; ventral outline straight; subpetiolar process acute, towards forward. In profile view, postpetiole shorter than petiole, lower than petiolar node; dorsal outline convex and ventral outline slightly concave; in dorsal view, wider than petiolar width, rounded. Gastral tergite I larger than remaining segments.

In full-face view, frons longitudinally striated, rest of dorsal surface of head reticulate. Clypeus smooth and shiny medially, lateral sides longitudinally striated. Frontal triangle smooth and shiny. Frontal lobes longitudinally striated. Mandibles smooth and shiny. Antennal scape smooth and shiny. Cervical shield punctate. Pronotum shiny and slightly wrinkled. Mesonotum, mesopleuron and propodeum reticulate. Legs smooth and shiny. Petiole reticulate. Disc of postpetiole smooth and shiny. Gastral tergite I smooth and shiny.

Dorsal surface of head with short decumbent hairs and long erect hairs; vertex with short decumbent hairs. Anterior median clypeus with two pairs of long erect hairs. Mandibles, masticatory margins with long decumbent hairs; surface with short decumbent hairs. Antennal scape with dense short decumbent hairs. Mesosoma with short decumbent hairs and long erect hairs; promesonotum with four pairs of long erect hairs, three of them situated at pronotum, one situated at mesonotum; propodeum with a pair of long erect hairs, situated at middle of dorsal outline of propodeum. Legs with short dense decumbent hairs. Petiolar node and postpetiole with long erect hairs. Gastral tergite I with long decumbent and sparsely erect hairs.

Head, mesosoma, waist, gaster brown. Antennae and legs yellowish brown.

Etymology.

The species is named after the strongly forked median clypeus of the minor worker.

Habitat.

The type specimens were collected from dead wood.

Distribution.

Vietnam ( Lao Cai, Ninh Binh, Quang Ninh and Bac Giang Province)

Remarks.

Three intermediates are recognized within the major worker subcaste of this species (Fig. 9 ). Number of ocelli is variable (one to three). Forward convexity of promesonotal suture in dorsal view is variable. Sculpture in upper part of mesopleuron is variable (smooth and shiny to reticulate).

This species corresponds to Oligomyrmex sp. eg- 1 shown in Eguchi et al. (2011).

Figures

Figure 8. A – F. Carebara bifida sp. nov. A – C. Holotype major worker (VNMN, collection code KUECCRB 016) from Vietnam; D – F. Paratype minor worker (KUEC, collection code KUECCRB 019) from Vietnam. A, D. Profile view of body; B, E. Head in full-face view; C, F. Dorsal view of body.

Figure 9. A – K. Intermediates of Carebara bifida sp. nov. A – E. Intermediate 1 (Paratype, SKYC, collection code KUECCRB 017); F – H. Intermediate 2 (Paratype, KUEC, collection code KUECCRB 023); I – K. Intermediate 3 (Holotype, VNMN, collection code KUECCRB 016). A, F, I. Head in full-face view; B, C, G, J. Profile view of body; D, E, H, K. Dorsal view of body.