Strumigenys masukoi

According to Imai et al. (2003), this species is very rarely collected in Japan, found only on the ﬂoor of broad-leaved forest. A single worker specimen of this species has been collected from a soil sample in the broad-leaved forest at an elevation above 1000m in Korea (Dong & Kim, 2020).

Identification
The only member of the Strumigenys baudueri-group that occurs in the eastern Palaeartic region.

Dong & Kim (2020) - This species can be distinguished from other Korean Strumigenys spp. by the combination of the following characteristics:
 * Head distinctly long and elongated in full-face view.
 * Apicoscrobal hair present, long, flagelliform in full-face view.
 * Anterior part of head including mandibles without long erect hairs in profile view.
 * Clypeus distinctly longer than wide.
 * Mandibles short, triangular shaped, always shorter than clypeal length.
 * Pronotal humeral hair present.
 * Body moderately covered with flagelliform hairs.

Ogata & Onoyama, 1998 - S. masukoi resembles Strumigenys kichijo in having elongate head, rounded anterior margin of clypeus, unelbowed antennal scape and flagellate hairs on head and mesosoma, but distinguished by the poorly developed lamellate appendages on propodeum and long erect hairs on hind tibiae and basitarsi. The species is very rare, known only from two localities.

Distribution based on Regional Taxon Lists
Palaearctic Region: Japan.

Nomenclature

 *  masukoi. Smithistruma masukoi Ogata & Onoyama, 1998: 283, figs. 12, 13 (w.) JAPAN. Combination in Pyramica: Bolton, 1999: 1673; in Strumigenys: Baroni Urbani & De Andrade, 2007: 123. See also: Bolton, 2000: 391.

Description
TL: 1.5-1.9 mm; HL 0.60-0.67 mm; HW 0.40-0.44 mm; CI 65-67; ML 0.10-0.13 mm; MI 15-22; SL 0.27-0.32 mm; SI 65-74; PW 0.27-0.28 mm; WL 0.59-0.63 mm (7 measured).

Head elongate with slightly convex dorsum, posterior margin roundly emarginate with low occipital carina. Mandibles small, convex dorsally; basal lamella on masticatory margin long and low followed by acute 7 teeth and by 6-7 minute apical ones. Labrum not dissected, but at least paired anterior lobes visible. Clypeus longer than wide, occupying about 1/3 of HL in length, slightly convex in the middle; anterior margin narrowly convex, but not forming a median lobe. Frontal lobels slightly raised. Frontal area depressed. Antennae 6-segmented; scapes slender, without subbasal elbows; second segment as long as following two segments together; apical segment as long as preceding four segments together. Eyes small, long as preceding four segments together. Eyes small, well convex, consisting of 4 to 7 facets, situated slightly before the posterior 1/3 of head length.

Dorsum of mesosoma without a distinct median longitudinal carina or lateral marginations in dorsal view; pronotum weakly marginate anteriorly, slightly arched dorsally, without distinct humeri; promesonotal suture indistinct dorsally; mesonotal dorsum slightly raised; hair wheel large and distinct; metanotal groove weakly impressed dorsally; propodeum with small dentiform projection posterodorsally, and with lamelliform appendages; propodeal spiracle situated near the base of propodeal spine. Petiole with narrow anterior peduncle and rounded node. Pospetiolar node broad, nearly twice as wide as petiolar node. Spongiform appendages on petiole and postpetiole well developed. Basal portion of first gastral tergite with 14 distinct striae, which are nearly same in length.

Mandibles and clypeus shallowly punctate, interspaces smooth and shining; the rest of head finely reticulate. Dorsal surfaces of mesonotum and propodeum, legs and petiole reticulate; the remainder of body smooth and shining. Mandibles covered with spatulate hairs, clypeus with broad spatulate hairs, which are longer intervals; dorsum of head, trunk, petiole and postpetiole with abundant hairs, most of which are short and decumbent, but some are extremely long and flagellate. Gastral dorsum sparsely with simple, long, and erect hairs. Besides abundant appressed hairs, hind tibia with 2 long erect hairs, and tarsus I with 2 long erect hairs (in some cases, apical one may subdecumbent). Body color reddish brown.

Bolton (2000) - TL 2.2-2.3, HL 0.61-0.63, HW 0.41-0.42, CI 65-69, ML 0.10-0.12, MI 15-19, SL 0.30-0.32, SI 72-77, PW 0.26-0.27, AL 0.58-0.60 (4 measured).

Counting from base of mandible teeth 1, 3 and 5 subequal in length, each distinctly longer than teeth 2 and 4; with 14 teeth and denticles in total. Clypeal dorsum smooth and shining, contrasting with the densely reticulate-punctate vertex. Hairs on dorsum of clypeus very short and spatulate, appressed. Hairs fringing the clypeal margins short spatulate and slightly projecting. With head in full-face view the dorsolateral margin with 2 projecting long flagellate hairs, the first is apicoscrobal, the second is on the side of the occipital lobe. Eye small but strongly convex, visible in full-face view. Leading edge of scape with short narrowly spoon-shaped hairs that are sharply angled toward the apex of the scape. Cephalic dorsum with dense curved narrowly spatulate ground-pilosity and with two pairs of standing flagellate hairs, one pair just in front of the highest point of the vertex, the other behind the highest point. Pronotal humeral hair flagellate. Pronotal dorsum smooth, the mesonotum densely reticulate-punctate. Propodeal dorsum almost smooth, with extremely faint punctulate sculpture; propodeal declivity smooth. Dorsal alitrunk with very dense fine curved ground-pilosity; a single pair of flagellate hairs at about the pronotal midlength and another pair present on the mesonotum. Legs densely clothed with soft appressed fine hairs, the tibiae and basitarsi also with freely projecting long flagellate hairs present. Petiole and postpetiole dorsally with short fine curved ground-pilosity and longer posteriorly curved simple hairs. First gastral tergite with numerous fine curved to flagellate standing hairs. Dorsum of petiole node weakly punctulate, the postpetiole disc and gaster glassy smooth. Petiole in dorsal view with spongiform lobes large, the lateral lobes strongly projecting and the thickness of the posterior collar about half the length of the disc of the node.

Type Material
Bolton (2000) - Holotype and paratype workers, JAPAN: Manazuru-misaki, Kanagawa Pref., Honshu, 3.vii.1983 (K. Masuko); paratype workers with same data but 21.vi.1982; other paratype workers, Mt Kakezuyama, Hiroshima Pref. (Y. Touyama) (ñ ) [examined].

Determination Clarifications
The species corresponds to S. sp 7. Of MSJ (1988) and Ogata & Onoyama (1992).

References based on Global Ant Biodiversity Informatics

 * Ogata K. and Onoyama K. 1998. A Revision of the Ant Genus Smithistruma Brown of Japan, with Descriptions of Four New Species (Hymenoptera: Formicidae). Entomological Science 1: 277-287