Strumigenys extemena group

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Strumigenys extemena group Bolton (2000)

Species

Malesian-Oriental-East Palaeartic

Worker Diagnosis

Mandibles stoutly elongate-triangular in full-face view; when fully closed the masticatory margins only engage in the apical halves or less of their length (usually from about tooth 9 to apex). Proximal to this with an elongate tooth -lined triangular space between the mandibles. Dorsal surface of each mandible near base with a very distinct sharp transverse edge or rim that extends across its width, parallel to the clypeal margin; the mandible surface between the rim and the clypeal margin appears in dorsal view as a deep transverse impression. In ventral view outer margin of mandible weakly inflected prebasally. MI 29-38.

Dentition. Mandible with 22-24 small teeth and denticles in total, without a distinct basal row of relatively larger teeth. Largest tooth may be the basal or tooth 2 or 3 from the base, but tooth 5, 6, or 7 is also enlarged, larger than those immediately preceding or following. Distal of tooth 9 the mandible curves abruptly downward, bears 12-14 minute teeth and denticles and terminates in a small apical tooth.

Basal lamella of mandible very small, low and rounded, followed by the basal tooth without a diastema.

Labrum terminates in a pair of narrow digitate to conical lobes.

Clypeus with anterior margin broad, evenly shallowly convex in full-face view or with the convexity accentuated in the small median area between the inner margins of the closed mandibles. True lateral margin of clypeus very short before merging with the preocular carina.

Clypeal dorsum either hairless, or with minute appressed pubescence, or with small appressed scale-like or orbicular hairs. Anterior and lateral margins of clypeus without projecting hairs.

Preocular carina conspicuous in full-face view.

Vertex at or close to its highest point traversed by a raised ridge or crest that may be bluntly rounded and indistinct through to acute and sharply defined.

Ventrolateral margin of head poorly defined in front of eye, well below level of lowest point of mandibular insertion and tending to terminate at the posterior margin of the buccal cavity. Postbuccal impression vestigial.

Cuticle of side of head within scrobe shagreenate to densely reticulate-punctate.

Scape very short to short, SI 49-57, narrow in its basal third, the leading edge immediately distal of the narrow portion may be strongly convex, distinctly angled, or project as a small subbasal lobe; scape broadest at this point.

Leading edge of scape distal to broadest point with a row of spatulate to spoon-shaped hairs that are small to minute and curved toward the apex of the scape; largest hair frequently at or very close to broadest point of scape.

Pronotum without a median longitudinal carina, bluntly to sharply marginate dorsolaterally and its dorsum flat to shallowly concave. In profile the mesonotum forms one or two separate convexities or humps behind the pronotum.

Propodeum with or without short triangular teeth that are emergent from the lamellae, but the latter always broadly present through the entire depth of the declivity.

Spongiform appendages of petiole and postpetiole large to massive, very conspicuous and sharply defined. Base of first gastral sternite in profile with a weak crest of spongiform tissue or without spongiform tissue.

Pilosity. Pronotal humeral hair absent or present; when present short and straight. Dorsolateral margins of head in full-face view without projecting hairs; apicoscrobal hair absent. Standing hairs sparse to absent on cephalic dorsum and alitrunk, present on first gastral tergite. Ground-pilosity of head absent to sparse, when present of minute inconspicuous appressed hairs. Dorsal (outer) surfaces of middle and hind tibiae with minute appressed apically directed hairs, without freely projecting elongate pilosity; extreme apex of tibia may have 1-2 specialised enlarged hairs overhanging the basitarsus.

Sculpture. Dorsum of head behind clypeus usually finely densely reticulate-punctate, rarely almost smooth. Pleurae and sides of propodeum smooth to weakly reticulate-punctate.

Disc of postpetiole smooth.

Notes

The only previously described species of this group, Strumigenys extemena, from Singapore, is the type-species of the now-abandoned genus Dysedrognathus (Bolton, 1999). Nine species are now known, ranging from Borneo and Sumatra to Nepal. All are very sparsely represented in collections and are apparently rare.

Taken together the nine share a remarkable mandibular structure that, whilst remaining within the limits of Pyramica, has a number of unique features, as described above and also discussed under individual species and in the gyges group notes. Without doubt the form of mandible evolved here forms the template from which the very specialized mandible seen in the murphyi group has developed. The other characters originally invoked to isolate Dysedrognathus grade morphoclinally back to Pyramica in the newly discovered species.

References

  • Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028.