Strumigenys extemena

Identification
Bolton (2000) - Within the group extemena is unique in its possession of small appressed scale-like hairs on the clypeus, on the cephalic dorsum immediately behind the clypeus and on the scapes. Such pilosity is absent or differently arranged in the other eight species. The petiole node in dorsal view (excluding the spongiform tissue) is about as broad as long in extemena but is conspicuously broader than long elsewhere in the group.

Only Strumigenys deinognatha has mandibles constructed the same as extemena. In both these species the masticatory margins are considerably elevated above the level of the outer margins, so that the dorsal surfaces fall away steeply on each side of the midline and the closed mandibles together are triangular in section or frontal view. Separation of these two is based on the characters given in the key.

Like Strumigenys carinognatha, Strumigenys atopogenys, Strumigenys ocypete and Strumigenys podarge, extemena has a transverse ridge across the widest point of the vertex and lacks standing hairs on the dorsal alitrunk. But in ocypete and podarge the scape at its widest point has a conspicuous large, anteriorly projecting specialised hair, elongate and remiform in podarge, flat and broadly scale-like in ocypete. In this respect extemena resembles Strumigenys acheron and Strumigenys aello where no specialised hair appears at this point, merely a continuation of the row of small curved hairs that occupies the remainder of the scape's leading edge.

The species acheron and aello have standing straight hairs present near the pronotal humeri and a single pair anteriorly on the mesonotum, and the former has a transverse ridge on the head that is as well developed as in extemena. These two species possess transverse rows of standing hairs on the vertex, with 4 hairs in a row. S. aello has two such rows, one across the highest point of the vertex and the second closer to the occipital margin, whilst acheron has only a single row close to the occipital margin. In extemena there are no standing hairs anywhere on the cephalic dorsum. Finally, the very distinct carinognatha, atopogenys and tarbosyne are immediately isolated by the structure of the basidorsal mandible, discussed under those species.

Like other members of the group extemena has a short, broad head and relatively long mandibles, CI 89, MI 38, with HW 0.40-0.41 and SL 0.24 (after Taylor, 1968b).

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia, Singapore.

Nomenclature

 *  extemena. Dysedrognathus extemenus Taylor, 1968d: 133, figs. 3, 4 (w.) SINGAPORE. Combination in Pyramica: Bolton, 1999: 1672; in Strumigenys: Baroni Urbani & De Andrade, 2007: 119. See also: Bolton, 2000: 419.

Type Material
Bolton (2000) - Holotype worker and paratype worker, SINGAPORE: Bukit Timah Nature Reserve, 8.iii.1965, berlesate no. B45, leafmould on granite, degraded coastal hill forest (D. H. Murphy) [examined].