Strumigenys nathistorisoc

Strumigenys nathistorisoc was only recorded in secondary forests and Feng Shui woods, along a relatively large gradient of elevation ranging from 29 to 572 m.

Identification
Dorsum of head, scape, and mandibles covered with appressed spatulate hairs, but no standing hairs. Side of mesosoma generally smooth and shining. Elongated propodeal spines subtended by narrow concave lamellae. Masticatory margin of mandibles engaging only at the apical half (or slightly less than half) of their lengths, with a prominent diastema proximal to this and first 3 preapical teeth not reaching their counterpart from the opposing mandible. Dentition consisting of a small conical tooth, a series of alternating long conical teeth and low round teeth, a crowded series of minute denticles at the down curvature of the apex of mandible, and a small conical apical tooth.

Strumigenys nathistorisoc is well distinguished from other Strumigenys species by a combination of the characteristics listed in the diagnosis. It does not fit the description of any existing Strumigenys species group, in particular due to its highly distinctive mandibles and dentition.

Comparing S. nathistorisoc with the most similar appearing Strumigenys species, such as Strumigenys kichijo and species from the S. leptothrix-group, these species, in contrast, are often either hairless or have simple or flagellate hairs on the cephalic and pronotal dorsum, or have sculpture on the sides of the mesosoma, or have propodeal spines subtended by medium to broad lamellae. S. nathistorisoc also lacks the laterally projecting hairs in full-face view or the distinct transverse striations on the pronotal dorsum and dorsum of the petiolar node that characterise Strumigenys nankunshana.

Focusing on the mandibles and dentition, in contrast to the description of S. nathistorisoc, S. kichijo has only conical teeth. S. nankunshana and species from the S. leptothrix-group have masticatory margins that engage throughout the entire length. Strumigenys wilsoniana has a much wider gap between the mandibles, the masticatory margins engage at the apical third (instead of around half as in S. nathistorisoc) of their length, with the basal 2 teeth (instead of 3) situated at around the mid-length of the mandible (instead of sparsely across the basal half of the mandible) and not reaching their counterparts from the opposing mandible when the mandibles are fully closed.

Distribution based on Regional Taxon Lists
Palaearctic Region: China.

Nomenclature

 *  nathistorisoc. Strumigenys nathistorisoc Tang, Pierce & Guénard, 2019: 31, figs. 12A-D (w.) CHINA.

Worker
Holotype: TL 3.2, HL 0.72, HW 0.57, MandL 0.24, SL 0.33, EL 0.068, PW 0.27, ML 0.79, PL 0.37, PH 0.15, DPW 0.15, PPL 0.26, GL 0.81, CI 79, MI 33, SI 58, OI 12, LPI 41, DPI 40. Paratype workers (n = 26): TL 2.9–3.3, HL 0.67–0.75, HW 0.51–0.60, MandL 0.22–0.25, SL 0.30–0.35, EL 0.064–0.080, PW 0.25–0.30, ML 0.75–0.86, PL 0.34–0.40, PH,0.15–0.18 DPW 0.14–0.17, PPL 0.22– 0.26, GL 0.72–0.87, CI 76–81, MI 30–34, SI 56–62, OI 11–15, LPI 42–45, DPI 39–44.

Head: In full-face view occipital margin deeply, evenly concave; occipital corners well developed and bluntly angular. Clypeus, with a broadly convex anterior margin, in full-face view roughly resembling an inverted diamond-shape, broader than long; with a clear colour differentiation from the rest of the cephalic dorsum. Scapes subcylindrical, marginated but not converging anteriorly to form a thin lamella at leading edge. Mandibles in full-face view elongate and narrow, linear and very slightly curved; basal lamellae low and broadly triangular, not fully visible at full closure of the mandibles; in profile view robust with the apical half enlarged, portion following midpoint distinctively raised then curving downwards apically. Masticatory margins engage only at apical half (or slightly less than half) of their lengths; proximal to this is a prominent diastema between the mandibles, through which the labral lobes are visible.

Dentition: Basal most preapical tooth small and conical, sometimes followed by a small denticle; the following tooth also conical, larger and longer; the third tooth low and rounded; in full-face view all first three teeth located on the basal half of the mandible and not reaching their counterpart from the opposing mandible when the mandibles are fully closed. Distal to these, the fourth tooth conical and slightly curved, being the longest of the preapical teeth; the fifth tooth low and rounded, sometimes almost squircle in shape, wider and longer than the third tooth; the sixth tooth conical, similar in length to second tooth; all these three teeth fully engaging with their counterparts from the opposing mandible and are visible in full-face view. Apex of mandible at the down curvature, in anterior view, with a crowded series of around 11 minute denticles, terminating with a small conical apical tooth.

Mesosoma: In profile view the dorsum of mesosoma more or less flat transversely, except for a slight depression at the mesonotum immediately posterior to the pronotum; pronotum marginate dorsolaterally. In dorsal view, lateral margins of the pronotum evenly convex. Propodeum spines elongate acute triangular, subtended on each side by a very narrow concave lamella that broadens slightly basally into a small rounded convex propodeal lobe.

Waist Segments: Petiole in profile elongate and subclavate; peduncle does not grade evenly into the node, and about as long as (or slightly shorter than) the node; node in dorsal view longer than broad. Disc of the postpetiole in dorsal view broader than long, and slightly shorter than petiolar node. Spongiform tissues present on both petiole and postpetiole; ventral lobes of petiole and postpetiole extensive; lateral lobe of petiole merely a small flap at the posterolateral angle of the node in profile; in dorsal view present along the posterior margin of the petiolar node, and surrounding the disc of postpetiole, thicker along the posterior margin than that on the anterior margin.

Pilosity: Cephalic dorsum in profile without standing hairs. In full-face view cephalic dorsum covered in rows of anteriorly directed appressed spatulate hairs that are slightly inclined toward the midline; no laterally projecting standing hair; cephalic dorsolateral margin, from the anterolateral margin of the occipital lobe to the frontal carina, with anteriorly directed appressed hairs; leading edge of scape with apically directed, appressed spatulate hairs, and an additional 2 or 3 rows of similar hairs on the surface of the scape. In full-face view, dorsal masticatory margin of mandibles with a row of anteriorly directed spatulate hairs that slightly inclined toward the midline; rest of dorsal surface of mandibles also densely covered in rows of similar hairs. Pronotal dorsum covered sparsely with appressed spatulate hairs directed toward the midline; row of similar appressed hairs on the dorsolateral margins of the pronotum. Propodeal dorsum with a few posteriorly directed, suberect to decumbent short simple hairs; a few similar hairs on the dorsolateral margin of the petiolar node and postpetiole. First gastral tergite with sparse, very short suberect simple hairs; in dorsal view with 1 or 2 pairs of simple apical erect hairs positioned laterally.

Sculpture: Cephalic dorsum, excluding clypeal dorsum, sparsely reticulate-rugulose, with spaces between rugulae densely areolate-rugulose; clypeal dorsum densely reticulate-rugulose; surface of antennal scrobe, antenna and mandibles densely reticulate-punctate. Pronotal dorsum faintly reticulate-rugulose; mesonotal and propodeal dorsum densely reticulate-punctate; side of mesosoma generally smooth and shining, with vestiges of sculpture around margins. Dorsum of petiolar node faintly reticulate-punctate; dorsum of postpetiole smooth and shining. Basigastral costulae short and inconspicuous, rest of gaster smooth and shiny.

Type Material

 * Holotype worker: HONG KONG: Islands District, Lantau Island, Sunset Peak, 22.263923N, 113.953762E, 467 m, 3 June 2015 (R.H. Lee) (collection code RHL-HK-LSP-T3WM) [IBBL, ANTWEB1016948].
 * Paratype workers (n = 26): same data as holotype.

Etymology
This species is named after the Hong Kong Natural History Society whose members graciously supported our work on the ants of Hong Kong.

References based on Global Ant Biodiversity Informatics

 * Tang K.L., Pierce M.P., and B. Guénard. 2019. Review of the genus Strumigenys (Hymenoptera, Formicidae, Myrmicinae) in Hong Kong with the description of three new species and the addition of five native and four introduced species records. ZooKeys 831: 1-48.