Strumigenys mnemosyne

Known from rainforest litter-samples.

Identification
Bolton (2000) - A member of the Strumigenys mnemosyne-group. The species Strumigenys daspleta, mnemosyne and Strumigenys runa, each known only from a holotype worker and all occurring in Borneo, form an exceptionally close complex. They hold most features in common but show some interesting differences that lead me to conclude that three distinct species are present rather than three individuals of a single variable form. Comparative characters that isolate the three species are as follows.

Elongate straight freely projecting hairs are present on the leading edge of the scape in both daspleta and runa; such hairs are absent in mnemosyne. In mnemosyne and runa the posterior margin of each occipital lobe has a minute indentation in the outline about half way between the end of the median collar and the lateral angle of the lobe; this indentation is covered and partly concealed by the fine cuticular carina that runs along the margin. In daspleta the indentation is much longer and deeper, and the cuticle spanning it forms an elongate fenestra or blister that occupies more than half the length between the median collar and the posterior angle.

Pilosity on the dorsum of the head and alitrunk is much denser in daspleta than in the other two and is short and stubbly, the hairs being too closely crowded to be counted easily. In mnemosyne hairs are much sparser, longer and blunted; they are few enough to be easily distinguished and counted on the dorsal head, and are arranged in pairs on the alitrunk. The situation in runa is intermediate between these two extremes, but in this species the dorsal outline of the pronotum in profile is concave in its posterior half while the other two are shallowly convex in this area. Finally, the petiole node in profile forms a high narrowly rounded anterior peak in mnemosyne and runa, posterior to which the dorsum slopes steeply away. In daspleta the entire dorsal node is more broadly and evenly rounded, without an obvious anterior peak.

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

Nomenclature

 *  mnemosyne. Pyramica mnemosyne Bolton, 2000: 446, figs. 266, 291 (w.) BORNEO. Combination in Strumigenys: Baroni Urbani & De Andrade, 2007: 124

Worker
Holotype. TL 1.4, HL 0.38, HW 0.30, CI 79, ML 0.07, MI 18, SL 0.16, SI 53, PW 0.18, AL 0.36. Leading edge of scape without elongate straight hairs that project anterodorsally. With head in full-face view the lateral margin from the frontal lobe to the occipital corner with 4 freely projecting stiff hairs. Posterior margins of occipital lobes in full-face view with a minute indentation on each side that is spanned by a small strip of cuticle. Standing hairs on dorsum of head sparse, straight to very slightly curved and appearing blunt apically. Cephalic hairs apparently arranged as follows, though some loss by abrasion may have occurred: an anterior pair (or broken transverse row) at about the level of the eye; a transverse row just in front of the highest point of the vertex; an irregular arched transverse row in front of the occipital margin. Dorsum and sides of head entirely unsculptured. Eye minute and inconspicuous, of a single tiny ommatidium. Upper scrobe margin not sharply defined posteriorly, rounded, especially behind the level of the eye; the scrobe itself shallow and indistinct. Pronotal dorsum evenly shallowly convex in profile. Alitrunk entirely smooth, standing hairs on the dorsum sparse, short and bristly, arranged in distinct pairs. Lamina on propodeal declivity narrowing dorsally, reaching higher than level of top of spiracle. Freely projecting long hairs on middle and hind tibiae and basi tarsi very conspicuous. Node of petiole in profile narrowly rounded, forming an anterior peak behind which the dorsum slopes steeply downward. Straight to weakly curved standing hairs numerous on waist segments and first gastral tergite. Petiole and disc of postpetiole unsculptured, first gastral tergite unsulptured except for the basigastral costulae. Petiole node in dorsal view broader than long, without a posterior collar.

Type Material
Holotype worker, Malaysia: Sarawak, 4th. Division, Gn. Mulu Nat. Pk RGS Expd., Long Pala, 26.ix.1977, lowl. rainforest leaf litter (B. Bolton).