Acanthomyrmex malikuli

Acanthomyrmex malikuli was found to nest in preformed cavities in hard dead wood on the forest floor in a lower tropical mountain forest (800–1000 m a.s.l.).

Identification
Jaitrong and Asanok (2019) - Acanthomyrmex malikuli can be distinguished from all other species in Acanthomyrmex luciolae group by the following combination of characters: 1) major and minor workers having dark brown to black body; 2) dorsum of head (in profile view) strongly convex in both castes; 3) major worker having anterior half of head rugulose with dense foveae between wrinkles; and 4) major and minor workers with dense erect hairs on the head and first gastral tergite. This species is most closely related to 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). This species is separated from Acanthomyrmex sulawesiensis by the presence of pronotal spine in ergatoid queen (without pronotal spine in Acanthomyrmex malikuli; with pronotal spine in Acanthomyrmex sulawesiensis); and major worker having anterior half of head rugulose with dense foveae between wrinkles (entire of head lacking rugae in Acanthomyrmex sulawesiensis). Acanthomyrmex malikuli differs from Acanthomyrmex dusun as follows: 1) anterior half of head rugulose with dense foveae between wrinkles in Acanthomyrmex malikuli (lacking rugae in Acanthomyrmex dusun); and 2) propodeal spine almost straight in Acanthomyrmex malikuli (short, cylindrical, curved ventrad in Acanthomyrmex dusun).

Distribution based on Regional Taxon Lists
Oriental Region: Thailand.

Nomenclature

 *  malikuli. Acanthomyrmex malikuli Jaitrong & Asanok, 2019: 116, figs. 1-3 (w.q.m.) THAILAND.

Worker
Holotype: HL 2.41, HW 2.18, EL 0.17, SL 1.06, HFL 1.29, CI 111, EI 8, HFI 59, SI 48.

Major workers (3 paratypes): HL 2.38–2.57, HW 2.08–2.24, EL 0.17–0.20, SL 1.09–1.12, HFL 1.29–1.32, CI 114–116, EI 8–9, HFI 59–62, SI 49–54. Non-type major workers (n = 5): HL 2.28–2.41, HW 2.01–2.15, EL 0.17–0.20, SL 0.99–1.09, HFL 1.16–1.25, CI 112–116, EI 8–10, HFI 57–60, SI 49–51.

Minor workers (10 paratypes): HL 0.92–1.06, HW 1.06–1.19, EL 0.13–0.17, SL 0.92–0.99, HFL 1.02–1.06, CI 88–91, EI 12–15, HFI 89–100, SI 81–88.

Major: Head, in full-face view, longer than broad, lateral cephalic margins weakly convex and posterior cephalic margin shallowly concave medially; cephalic median furrow well-developed, extending anteriad to frontal area; in dorsal view, posterior half of head foveate with smooth and shiny interspaces, anterior half of head rugulose with dense foveae between wrinkles; foveae on posterior cephalic half smaller than those on anterior half; dorsum of head covered entirely with dense short erect hairs; mandible massive, subtriangular and subopaque; masticatory margin straight without distinct denticles; basal margin of mandible weakly concave; mandible with few hairs along masticatory margin; anterior margin of clypeus lacking medial and lateral setae, mid anterior margin of clypeus shallowly concave; median portion of clypeus smooth and shiny; frontal lobe poorly developed, only partly covering antennal socket; frontal carina conspicuous, reaching mid-length of head; antennal scrobe deep and conspicuous, with 3–5 irregular 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 (clavate, its apical portion narrower than antennal segments X–XII) and short, when laid backward not extending beyond mid-length of head; scape with more than 15 long erect hairs. Mesosoma short and stout; mesonotum almost straight, with sparse erect hairs; promesonotal suture present as weak groove dorsally; pronotal spine absent; metanotal groove indistinct; propodeal spine, in profile, relatively broad basally and almost straight apically, largely smooth and shiny, without erect hairs and decumbent hairs; legs entirely with numerous erect hairs; anterior face of each femur smooth and shiny, posterior face superficially reticulate with smooth and shiny interspaces. Petiole, in profile, with long anterior pedicel, usually a pair of posterolateral hairs present; petiolar node, in profile, subtriangular with sharp angle dorsally; posterior face of petiolar node with 2 or 3 pairs of erect hairs; in posterior view dorsum of petiolar node with pair of blunt angles, dorsal outline between angles weakly concave; postpetiole cylindrical, slightly shorter than high, in dorsal view with parallel sides and in profile with straight dorsal outline; postpetiole entirely rugose; dorsum of postpetiole with sparse erect hairs. Gaster smaller than head; gastral tergite I circular, smooth and shiny and 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.

Minor: Head, in full-face view, slightly shorter than broad, with convex lateral margins and weakly concave posterior margin; head entirely coarsely punctorecticulate, punctures large, 0.07–0.13 mm in diameter; cephalic dorsum 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 masticatory margin; anterior clypeal margin armed with 5 teeth, with long 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; eye relatively small, located anterior to mid-length of head, moderately protruding breaking outer margin of head; antenna 12-segmented with 3-segmented club; antennal scape slender, when laid backward surpassing cephalic corner by 1.5 times width of antennal scape; antenna with dense long erect hairs. Mesosoma, in profile, relatively stout, its dorsum sparsely with erect hairs; promesonotum convex and sloping gradually to metanotal groove; pronotum with a pair of long and sharp spines; promesonotal suture absent dorsally; metanotal groove present as inconspicuous broad impression just anterior to base of propodeal spine; propodeal spine in profile relatively long, its basal half straight and apical half gradually down-curved; propodeal spine largely smooth and shiny, without erect hairs or decumbent hairs; legs with numerous erect hairs; anterior face of each femur smooth and shiny, posterior face superficially reticulate with smooth and shiny interspaces. Petiole, in profile, with long anterior pedicel; petiolar node, in profile, moderately to strongly raised, with relatively angulate apex, in posterior view with concavity between acute lateral sharp spines or angles; posterior face of petiolar node with a pair of erect hairs; postpetiole rectangular, shorter than high, in dorsal view with parallel sides and in profile with straight dorsal outline; postpetiole entirely rugose, its dorsum with dense erect hairs. First gastral tergite suboval, smooth and shiny and with dense erect hairs. Body entirely reddish brown to dark brown, gaster darker than head and mesosoma; mandible antenna and legs reddish brown to yellowish brown.

Queen
Dealate queen (paratype): HL 1.75, HW 1.95, EL 0.30, SL 1.06, HFL 0.96, MNH 168, MSW 1.39, CI 90, EI 15, HFI 68, MNI 82, MSI 71, SI 49. Non-type dealate queens (n = 4): HL 1.65–1.68, HW 1.85, EL 0.26–0.30, SL 0.92–0.96, HFL 1.29–1.32, MNH 162–168, MSW 1.35–1.39, CI 89–91, EI 14–16, HFI 68–71, MNI 82–84, MSI 72–74, SI 49–52.

Ergatoid queens (3 paratypes): HL 1.98–1.05, HW 2.01–2.05, EL 0.23–0.26, SL 0.92–0.96, HFL 1.25, CI 98–100, EI 11–13, HFI 61–62, SI 46–47. Non-types (n = 2): HL 2.08–2.15, HW 2.05–2.08, EL 0.26, SL 0.96, HFL 1.25, CI 102–103, EI 13, HFI 61–62, SI 46–47.

Dealate: Head, in full-face view, subrectangular, shorter than broad, with parallel sides and weakly concave posterior margin medially; 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 2 or 3 small denticles near basal angle; basal margin weakly concave without denticles; median portion of anterior clypeal margin weakly produced anteriad, with weak concavity at middle of anterior portion, lacking medial and lateral setae; median portion of clypeus superficially reticulate with smooth and shiny interspaces; 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 mid-length of head; ocelli present, in full-face view median ocellus slightly larger than 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 cephalic by 2 times width of antennal scape; scape with sparse long erect hairs. Mesosoma enlarged and high, its dorsum with erect hairs; pronotum in dorsal view narrow, without anterolateral spine; promesonotal suture distinct; scutellum in profile with convex dorsal outline, in dorsal view large and subtrapezoidal; mesoscutellum in dorsal view subrectangular with posterior margin weakly concave; mesoscutellum demarcated from mesoscutum by deep groove, in profile mesoscutellum protruding posteriorly; propodeal spine in profile relatively broad basally and weakly down-curved, smooth and shiny, without erect hairs and decumbent hairs; legs with sparse erect hairs, smooth and shiny. Petiole in profile with long anterior pedicel, petiolar node in profile with flat anterior face, weakly convex posterior face and acutely angulate dorsum; 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, area between angles weakly convex; postpetiole rectangular, slightly shorter than 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 circular, smooth and shiny, with dense erect hairs. Head, mesosoma, petiole and pospetiole reddish brown to dark brown; gaster darker than head and mesosoma or often black; mandible and legs reddish brown.

Ergatoid: Apterous. Similar to the major worker in structure, sculpture, coloration and pilosity, with the following conditions that should be noted: head slightly shorter and narrower (HW 2.02–2.05 mm, CI 102–103 in ergatoid queen; HW 2.08–2.24 mm, 112–116 in major worker); ocelli present, median ocellus in full-face view almost located at level of posterior margin of eye and almost as large as lateral ocelli; mesoscutellum protruding posteriorly.

Male
Male (paratype): HL 0.66, HW 0.83, EL 0.30, SL 0.20, HFL 1.02, MNL 0.99, MSW 0.89, CI 80, EI 36, HFI 124, MNI 90, MSI 108, SI 24. Non-types (n = 5): HL 0.69–0.73, HW 0.86–0.92, EL 0.33–0.36, SL 0.17–0.20, HFL 1.02–1.12, MNL 0.96–1.06, MSW 0.89–0.92, CI 78–82, EI 36–41, HFI 115–126, MNI 88–93, MSI 100–104, SI 19–22.

Paratype and non-types - Body black, but apical part of antenna, legs, and gaster reddish brown; wings light brown. Head in full-face view clearly broader than long, posterior margin almost straight; anterolateral part of head in which eye is located well produced laterally; mandible subtriangular, its masticatory margin with a large apical tooth, followed by 5 teeth including basal tooth; anterior clypeal margin roundly convex with weak median concavity; frontal lobe, frontal carina and antennal scrobe absent; ocelli present, with diameter less than distance between them; with head in full-face view median ocellus located a little behind level of posterior margin of eye; antenna 13-segmented, without club; antennal scape short when laid backward not reaching level of posterior margin of compound eye; antennal segment II very short; III much longer than broad and longer than each of segments IV–X. Mesosoma short and high; pronotal spine absent; mesoscutellum in profile strongly raised dorsoposteriad, in dorsal view with straight posterior margin; 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 clearly longer than high and cylindrical. Gaster relatively small and oval. Legs relatively long, smooth and shiny. Body sculpture basically as in Figure 3A–C.

Type Material
Holotype major worker (THNHM-I-00124, ), W Thailand, Tak Prov., Umphang Dist., Thung Yai Naresuarn East W.S., Thung Nanoi Forest Ranger Station, 15.50444°N, 98.95333°E, 18.II.2015, W. Jaitrong leg., colony no. TH15-WJT-321. Paratypes: 1 dealate queen (THNHM-I-00115, THNHM), 3 major workers (THNHM-I-00121 to THNHM-I-00123, THNHM), and 56 minor workers (THNHM-I-00119 to THNHM-I-00120 and THNHM-I-00125 to THNHM-I-00178), same data as holotype (,, THNHM, ); 3 ergatoid queens (THNHM-I-01195, THNHM), 10 minor workers (THNHM-I-01196, THNHM, SKYC), 1 male (THNHM-I-01194, THNHM), W Thailand, Tak Prov., Umphang Dist., Thung Yai W.S., Bae Ki Station, 24.IX.2016, W. Jaitrong leg., colony no WJT240916-6.

Etymology
The specific name is dedicated to Mr Vichai Malikul, Scientific Illustrator, Department of Entomology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. (, U.S.A.), who kindly helped W. Jaitrong when he visited the USNM.