Strumigenys circothrix

A rare species found of the forest floor of broadleaf forest or at forest margins and nesting in soil (Ogata & Onoyama 1998).

Identification
Bolton (2000) - A member of the Strumigenys circothrix-group. Characters separating this species from its only close relative, Strumigenys hiroshimensis, are given under the latter name.

Distribution based on Regional Taxon Lists
Palaearctic Region: Japan.

Nomenclature

 *  circothrix. Smithistruma circothrix Ogata & Onoyama, 1998: 280, figs. 3, 4 (w.) JAPAN. Combination in Pyramica: Bolton, 1999: 1673; in Strumigenys: Baroni Urbani & De Andrade, 2007: 117. See also: Bolton, 2000: 410.

Worker
TL: 1.0-1.2 mm; HL: 0.45-0.47 mm; HW: 0.38 mm; CI 82-85; ML: 0.08-0.12 mm; MI: 19-25; SL 0.18-0.20 mm; SI 48-52; PW: 0.20-023 mm; WL: 0.43-0.45 mm (3 measured).

Head longer than wide; posterior half of lateral borders of head roundly convex in full face view; posterior border concave with low occipital carina. Mandibles short, shorter than clypeus. Clypeus wider than long, with straight anterior margin and rounded corners, fringed with spatulate hairs. Antennae 6-segmented, scape slightly longer than apical segment of antenna, outer margin of scape angulate at the basal ¼; apical segment longest, about twice as long as funiculi 3 and 4 together. Eyes small, consisting of 3-5 facets; the diameter shorter than the length of subapical segment of antenna. Pronotum marginate anteriorly, but not laterally; promesonotal area slightly raised in profile; pronotal humeri not distinct; metanotal groove obsolete. Propodeum with more or less distinct lamellae (infradental lamella) at posterior margin; propodeal spines small and narrow. Petiole with spongiform appendages on ventral margin, and in posterior and lateral portions of node; node weakly raised in profile, slightly longer than wide in dorsal view. Disc of postpetiole surrounded with spongiform appendages, but rather thing, its thickness of each side narrower than the dorsal width of hind femur. First gastral tergite with basigastral costulae.

Ground surface of head and mesosoma reticulate-punctate, but smooth and shining on lateral surfaces of pronotum, mesopleuron and propodeum.

Hairs on head and mesosoma suborbicular; those on petiole, postpetiole and gaster spatulate or spoon-shaped. Dorsum of petiolar node with 2 pairs of spoon-shaped hairs, one anterolaterally and another posterolaterally. Body color yellow to reddish brown.

Bolton (2000) - TL 1.7-1.9, HL 0.45-0.48, HW 0.37-0.39, CI 80-85, ML 0.08-0.12, MI 20-25, SL 0.18-0.23, SI 50-59, PW 0.20-0.24, AL 0.45-0.48 (4 measured).

Basal tooth of mandible the longest; basal and third teeth narrowly conical and acute, contrasting strongly with the lower, broadly rounded second tooth; these visible in full-face view when mandibles fully closed. With head in full-face view all hairs on dorsum suborbicular; those on clypeus small, those on frons and vertex larger. Hairs fringing clypeus and dorsolateral margins of head broadly spoon-shaped to suborbicular, curved anteriorly and closely applied to the surface; without specialised freely projecting elongate hairs of any form anywhere on the sides or dorsum of the head. Small flat scale-like hairs present on mandibles and dorsa of scapes. Hairs on leading edge of scape that curve toward apex of scape largest basally, proximal of the broad subbasal curve of the margin. Dorsum of head uniformly finely reticulate-punctate. Pronotal humeral hair very short, stout and clavate. Promesonotal dorsum with scattered small appressed flattened hairs, the mesonotum with a single pair of short straight clavate hairs that are about equal in length to those at the pronotal humeri. Apically thickened to clavate standing hairs present on petiole and postpetiole, numerous on gaster. Dorsal (outer) surfaces of middle and hind tibiae with small broad hairs that are curved apically and closely applied to the surface. Pronotal dorsum with feeble faint longitudinal costulae, the surface between them faintly superficially punctulate. Mesonotum and propodeal dorsum more conspicuously reticulate-punctate. Side of alitrunk smooth and shining except near the dorsum. Petiole in dorsal view broader than long, the lateral spongiform lobes and posterior collar distinct. In profile the lateral spongiform lobe of the petiole confined to the posterolateral angle. Disc of postpetiole glassy smooth, much broader than long, with evenly convex lateral margins. Lateral and ventral spongiform lobes of postpetiole in profile both at least equal in area to the exposed disc, the ventral lobe larger than the lateral. Basigastral costulae short but strongly developed, arising across the entire width of the tergite.

Queen
TL: 1.4 mm; HL: 0.53 mm; HW: 0.42 mm; CI: 78; ML: 0.13 mm; MI: 25; SL: 0.25 mm; SI: 60; PW: 0.25 mm; WL: 0.57 mm. (1 measured).

Type Material
Bolton (2000) - Holotype and paratype workers, JAPAN: Ryukyus, Ishigaki I., Mt Banna, 20.vi.1991 (K. Morimoto); paratype workers and queen, Kumejima I., Ryukyus, 19.viii.1983 (H. Takamine); Nago, Okinawa I., Ryukyus, 27.vi.1974, (T. Abe) [examined].

Determination Clarifications
The species corresponds to Smithistruma sp. of Onoyama (1976), and was treated as S. sp. 8 of MSJ (1988) and Ogata & Onoyama (1992) with a Japanese name, Maruge-uroko-ari.

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
 * Shimono A., and S. Yamane. 2003. Ant species diversity on Okinoerabu-jima, the Ryukyus, southern Japan. For the Establishment of Remote Islands Study (Kagoshima Univ.) 3: 11-29.
 * Terayama M., S. Kubota, and K. Eguchi. 2014. Encyclopedia of Japanese ants. Asakura Shoten: Tokyo, 278 pp.
 * Yamane S. 2016. How many species of Ants in Amami Islands? (in Japanese). Part 2, chapter 1 in How many species of Ants in Amami Islands? Pp. 92-132.
 * Yamane S., S. Ikudome, and M. Terayama. 1999. Identification guide to the Aculeata of the Nansei Islands, Japan. Sapporo: Hokkaido University Press, xii + 831 pp. pp, 138-317.
 * Yamane S.; Ikudome, S.; Terayama, M. 1999. Identification guide to the Aculeata of the Nansei Islands, Japan. Sapporo: Hokkaido University Press, xii + 831 pp. pp138-317.