Acanthomyrmex mizunoi

Acanthomyrmex mizunoi, only known from Thailand, inhabits highlands and nests in soil. The type series and non-types were collected from Nakhon Nayok and Nakhon Ratchasima Provinces in a primary hill evergreen forest (ca 800 m a.s.l.). A colony (Colony no. RM-65) from the Chiang Rai Province, northern Thailand was collected in a coffee plantation (ca 900 m a.s.l.).

Identification
Jaitrong and Asanok (2019) - Acanthomyrmex mizunoi can be distinguished from all other species in A. luciolae group by the following combination of characters: 1) major and minor workers having reddish brown to dark brown body; 2) in major worker, anterior dorsum of head lacking rugae; 3) major worker with sparse shallow foveae on dorsum of head; 4) head with dense erect hairs in both castes; 5) major worker without erect hairs on dorsum of each femur; and 6) minor worker with fewer than 10 erect hairs around anterior portion of first gastral tergite. This species is most similar to Acanthomyrmex malikuli. However, it is easily distinguishable from the latter by the following characteristics: 1) in the major worker, anterior dorsum of head lacking rugae in Acanthomyrmex mizunoi (rugulose in Acanthomyrmex malikuli); 2) postpetiole clearly shorter than high in Acanthomyrmex mizunoi (almost as long as high, with straight dorsal outline in Acanthomyrmex malikuli); 3) first gastral tergite with very short appressed hairs in Acanthomyrmex mizunoi (without very short appressed hairs in Acanthomyrmex malikuli); 4) dorsal and lateral faces of femora without hairs in Acanthomyrmex mizunoi (with erect hairs in Acanthomyrmex malikuli); 5) in the minor worker, first gastral tergite without or with 1–4 erect hairs in Acanthomyrmex mizunoi (with dense erect hairs in Acanthomyrmex malikuli); 6) in the ergatoid queen, mesoscutellum not protruding posteriorly in Acanthomyrmex mizunoi (protruding posteriorly and overhanging narrow metanotum in Acanthomyrmex malikuli); 7) in the male, mesopleuron almost smooth in Acanthomyrmex mizunoi (strongly sculptured in Acanthomyrmex malikuli); and 8) postpetiole in profile clearly shorter than high in Acanthomyrmex mizunoi (as long as high and cylindrical in Acanthomyrmex malikuli). Acanthomyrmex mizunoi is also similar to Acanthomyrmex crassispinus in terms of the general appearance of the minor worker. After careful examination of the holotype and paratype workers of Acanthomyrmex mizunoi with non-type workers of Acanthomyrmex crassispinus from Taiwan, Orchid Island, 13.III.2017, collected by P.C. Hsu, we concluded that Acanthomyrmex mizunoi can be easily distinguished from the latter by the following characteristics: 1) major worker with dense erect hairs on the head and first gastral tergite in Acanthomyrmex mizunoi (completely without hairs in Acanthomyrmex crassispinus); 2) propodeal spine thin and cylindrical in Acanthomyrmex mizunoi (flat and broad at the base in Acanthomyrmex crassispinus); 3) minor worker having a petiole and postpetiole with sparse erect hairs in Acanthomyrmex mizunoi (without hairs in Acanthomyrmex crassispinus); and 4) first gastral tergite with 1–4 erect hairs in Acanthomyrmex mizunoi (without hairs in Acanthomyrmex crassispinus). A specimen (CASENT0101994ANTWEB; images available on Antweb), collected from Khao Yai National Park, Thailand, has been identified as Acanthomyrmex crassispinus. Images of this specimen agree well with the minor worker of Acanthomyrmex mizunoi in having dense erect hairs on the head, with sparse erect hairs on the petiole and postpetiole. Thus, this specimen (CASENT0101994ANTWEB) should be reidentified as a non-type of our new species, Acanthomyrmex mizunoi. The new species can be easily distinguished from Acanthomyrmex padanensis by the following characteristics: 1) in major worker, mid anterior margin of clypeus shallowly concave (anterior clypeal margin weakly convex in Acanthomyrmex padanensis); 2) in major worker, head with denes erect hairs (without hairs in Acanthomyrmex padanensis); and 3) in ergatoid queen, without pronotal spine, general shape as in major worker (with pronotal spine, general shape as in minor worker in Acanthomyrmex padanensis).

Distribution based on Regional Taxon Lists
Oriental Region: Thailand.

Nomenclature

 * . Acanthomyrmex mizunoi Jaitrong & Asanok, 2019: 124, figs. 4-6 (s.w.q. ergatoid q.m.) THAILAND.{nomenplus}}

Worker
Holotype major: HL 2.67, HW 2.24, EL 0.23, SL 1.06, HFL 1.29, CI 84, EI 10, HFI 57, SI 47.

Major workers (6 paratypes): HL 2.48–2.67, HW 2.05–2.28, EL 0.17–0.20, SL 0.96–1.02, HFL 1.22–1.35, CI 83–85, EI 8–9, HFI 56–60, SI 45–47.

Minor workers (10 paratypes): HL 0.96–1.02, HW 1.02–1.09, EL 0.13–0.17, SL 0.79–0.86, HFL 0.96–1.02, CI 106 110, EI 12–16, HFI 91–97, SI 73–81.

Major worker: Head, in full-face view, clearly longer than broad, lateral cephalic margins straight, posterior cephalic corners rounded, and posterior cephalic margin shallowly concave medially; cephalic median furrow well developed, extending anteriad to frontal area; dorsum of head entirely with dense erect hairs; mandible massive, subtriangular and superficially reticulate with smooth and shiny interspaces; masticatory margin without distinct denticles; basal margin weakly concave; mandible with few hairs along its masticatory margin and outer margin; median portion of anterior clypeal margin weakly produced anteriad, produced portion with anterior margin weakly concave at middle; clypeus lacking medial and lateral setae; median portion of clypeus smooth and shiny; frontal lobe poorly developed, partly concealing antennal socket; frontal carina conspicuous, reaching midlength of head; antennal scrobe deep and conspicuous, with 8–10 longitudinal ridges running from lateral portion of clypeus; eye relatively small, weakly convex, located at anterior ¼ of head length laterally; antenna 12-segmented with 3-segmented club; antennal scape thin and short, not extending beyond midlength of head; scape with more than 15 long erect hairs. Mesosoma short and stout; pronotal spine absent; mesonotum weakly convex, with sparse erect hairs; promesonotal suture present as a weak groove dorsally; metanotal groove present as inconspicuous, broad impression just in front of base of propodeal spine; propodeal spine in profile relatively broad basally and sharp apically, largely smooth and shiny, without erect hairs and decumbent hairs; dorsum of each femur without erect hairs; legs smooth and shiny. Petiole in profile with long anterior pedicel, usually a pair of posterolateral hairs present; petiolar node, in profile, subtriangular with blunt angle dorsally; posterior face of petiolar node with 2 or 3 pairs of erect hairs; in posterior view dorsum of petiolar node with a pair of blunt angles, dorsal outline between angles strongly concave; postpetiole clearly shorter than high, in dorsal view rectangular with parallel sides and in profile with convex dorsal outline; dorsum of postpetiole with sparse erect hairs; postpetiole entirely rugose. Gaster smaller than head; gastral tergite I circular, smooth and shiny and with dense erect hairs. Body sculpture basically as in Figure 4A–C. Head, mesosoma, petiole, and postpetiole reddish brown; gaster darker than head, mesosoma and waist often black; mandible and legs reddish brown but paler than head.

Minor worker: Head, in full-face view, slightly shorter than broad, with slightly convex sides and strongly concave posterior margin; head entirely coarsely punctorecticulate, punctures large, 0.07–0.13 mm in diameter; dorsum of head entirely with dense erect hairs; mandible massive, subtriangular and superficially reticulate with smooth and shiny interspaces; masticatory margin with few ill-defined denticles; basal margin almost straight; mandible with few hairs along its masticatory margin and outer margin; anterior clypeal margin armed with several teeth, with conspicuous median and lateral setae; median portion of clypeus with two distinct longitudinal ridges; frontal lobe poorly developed, partly concealing antennal socket; frontal carina conspicuous, reaching 2/3 of head length; antennal scrobe deep and conspicuous; compound eye relatively small, moderately protruding, located anterior to mid-length of head; antenna 12-segmented with 3-segmented club; antennal scape slender, when laid backward surpassing posterolateral corner of head by 1.2 times width of antennal scape; antenna with dense long erect hairs. Mesosoma in profile relatively stout, its dorsum sparsely with erect hairs; pronotum with a pair of straight spines, which are clearly shorter than propodeal spine; promesonotum convex and sloping gradually to metanotal groove; promesonotal suture absent dorsally; metanotal groove present as inconspicuous broad impression just anterior to base of propodeal spine; propodeal spine in profile relatively long and slender, gradually down-curved, largely smooth and shiny, without erect hairs and decumbent hairs; all femora smooth and shiny, dorsally without erect hairs. Petiole in profile with long anterior pedicel; petiolar node in profile moderately to strongly raised, with relatively angulate apex, in posterior view with strong concavity between acute lateral sharp spines or angles; posterior face of petiolar node with a pair of erect hairs; postpetiole rectangular, almost as long as high, in dorsal view with parallel sides and in profile with straight dorsal outline; postpetiole entirely rugose, its dorsum with sparse erect hairs. First gastral tergite suboval, smooth and shiny and with less than 10 erect hairs around anterior portion. Body entirely yellowish brown to reddish brown, gaster darker than head and mesosoma; mandible, antenna and legs yellowish brown to reddish brown but paler than head.

Queen
Dealate queens (3 paratypes): HL 1.78–1.82, HW 1.98–2.01, EL 0.23, SL 0.92– 0.96, HFL 1.35–1.39, MNL 1.75–1.78, MSL 1.39–1.42, CI 109–111, EI 11–12, HFI 68–70, MNI 79–80, MSI 70–72, SI 47–48.

Ergatoid queens (4 paratypes): HL 2.18–2.24, HW 1.95–2.01, EL 0.20, SL 0.92–0.96, HFL 1.19–1.25, CI 89–91, EI 10, HFI 60–63, SI 47–48.

Dealate: Head, in full-face view, subrectangular, shorter than broad, slightly broader posteriorly, with concave posterior margin; cephalic median furrow well developed, extending anteriad to frontal area; dorsum and lateral face of head foveate with smooth and shiny interspaces; dorsum of head entirely with dense erect hairs; mandible massive, subtriangular and superficially reticulate with smooth and shiny interspaces; masticatory margin straight with 3 or 4 small denticles near basal angle; basal margin weakly concave without denticles; median portion of anterior clypeal margin weakly produced anteriad, anterior margin of the produced portion concave at middle, with medial seta; median portion of clypeus smooth and shiny; frontal lobe poorly developed, partly concealing antennal socket; frontal carina conspicuous, reaching 2/3 of head length; antennal scrobe deep and conspicuous; eye relatively large, convex, located anterior to midlength of head; ocelli present, median ocellus, in full-face view, almost as long as lateral ocelli and almost located at level of posterior margin of eye; antenna 12-segmented with 3-segmented club; antennal scape thin and short, when laid backward surpassing midlength of head by 2.5 times width of antennal scape; scape with sparse long erect hairs. Mesosoma enlarged and high, its dorsum with erect hairs; pronotum narrow, without spine; promesonotal suture distinct; scutellum in profile with strongly convex dorsal outline, in dorsal view large and subtrapezoidal; mesoscutellum in dorsal view subrectangular with posterior margin weakly concave, demarcated from mesoscutum by deep groove, mesoscutellum protruding posteriorly and overhanging narrowed metanotum; propodeal spine in profile relatively broad basally and weakly down-curved, smooth and shiny, without erect hairs and decumbent hairs; dorsum of each femur without erect hairs; legs smooth and shiny. Petiole in profile with long anterior pedicel, 1 or 2 pairs of posterolateral hairs present; petiolar node in profile subtriangular with blunt angle dorsally; posterior face of petiolar node with 2 or 3 pairs of erect hairs; in posterior view dorsum of petiolar node with a pair of blunt angles, dorsal outline between angles strongly concave; postpetiole clearly shorter than high, in dorsal view rectangular with parallel sides and in profile with convex dorsal outline; dorsum of postpetiole with sparse erect hairs; postpetiole entirely rugose. First gastral tergite oval, smooth and shiny, with dense erect hairs. Head, mesosoma, petiole, and pospetiole reddish brown to dark brown; gaster darker than head and mesosoma, often black; mandible and legs reddish brown, always paler than head.

Ergatoid: Apterous. Similar to the major worker in structure, sculpture, coloration and pilosity, with the following conditions that should be noted: relatively smaller (HW 1.95–2.01 mm in ergatoid queen, 2.05–2.28 mm in major worker); median ocellus present; lateral ocelli absent; body colour paler than in major worker.

Male
Paratype: HL 0.69, HW 0.86, EL0.30, SL 0.17, HFL 1.06, MNL 0.96, MSW 0.83, CI 124, EI 35, HFI 123, MNI 86, MSI 96, SI 19. Non-type (n = 5): HL 0.66–0.73, HW 0.86–0.89, EL 0.26–0.30, SL 0.17–0.20, HFL 1.0–1.06, MNL 0.96–0.99, MSW 0.86–0.89, CI 123–130, EI 30–33, HFI 115–119, MNI 90, MSI 96–100, SI 19–22.

Body dark brown, but apical part of antenna, legs, and gaster reddish brown; wings light brown. Head, in full-face view, broadened-subpentagonal, posterior margin almost straight; anterolateral part of head in which compound eye is located well produced laterally; mandible subtriangular, masticatory margin with large apical tooth, followed by 5 teeth including basal tooth; anterior clypeal margin roundly convex; frontal lobe, frontal carina and antennal scrobe absent; ocelli present, with diameter less than distance between them; median ocellus, in full-face view, located slightly behind level of posterior margin of eye and slightly larger than lateral ocelli; antenna 13-segmented, without club; antennal scape short, when laid backward not reaching level of posterior margin of eye; antennal segment II very short; III much longer than broad and longer than each of segments IV–X; IX narrower and shorter than VIII and X. Mesosoma short and high; pronotal spine absent; mesoscutellum in profile strongly raised posterodorsally, in dorsal view with straight posterior margin, demarcated from mesoscutum by deep and broad groove; mesoscutellum strongly convex; posterolateral part of propodeal dorsum in profile forming a blunt angle. Petiole, in profile, with long anterior pedicel; petiolar node in profile very low and bluntly raised; postpetiole almost as long as high and its dorsal outline convex. Gaster relatively small and oval. Legs relatively long, smooth and shiny.

Type Material
Holotype major worker (THNHM-I-01197, ), central Thailand, Nakhon Nayok Prov., Muang Dist., Ban Hin Tang, 14.40611°N, 101.37139°E, 22.X.2017, W. Jaitrong leg., colony no. WJT221017-12. Paratypes: 5 major workers (THNHM-I-01198,, , THNHM), 64 minor workers (THNHM-I-01199, MHNG, SKYC, THNHM, ) and 3 dealate queens (THNHM-I-01200, SKYC, THNHM), same data as holotype; 4 ergatoid queens (THNHM-I-00054, THNHM-I-00061, THNHM-I-00063, THNHM-I-00065, SKYC, THNHM), 8 minor workers (THNHM-I-00055, THNHM-I-00057 to THNHM-I-00060, THNHM-I-00062, THNHM-I-00064, THNHM-I-00066, SKYC, THNHM, USNM), and 1 male (THNHM-I-00056), NE Thailand, Nakhon Ratchasima Prov., Pak Chong Dist., dry evergreen forest, 31.V.2000, W. Jaitrong leg., colony no. WJT310500-1; 1 ergatoid queen (THNHM-I-0053, THNHM) and 1 male (AMK007, THNHM), NE Thailand, Nakhon Ratchasima Prov., Khao Yai N.P., hill evergreen forest, 30.V.2000, C. Bourmas leg.

Etymology
The specific name is dedicated to Mr Riou Mizuno (Kagawa University, Japan), who confirmed the ergatoid queen of this new species and donated to us the specimens collected from the Chiang Rai Province.

References based on Global Ant Biodiversity Informatics

 * Jaitrong W., and L. Asanok. 2019. Two new species of the ant genus Acanthomyrmex Emery, 1893 (Hymenoptera, Formicidae, Myrmicinae) from Thailand. ZooKeys 842: 113-134.