Strumigenys akalles group

Strumigenys akalles group Bolton (2000)

Species

Malesian-Oriental-East Palaeartic

Worker Diagnosis

Apical fork of mandible with 3 teeth in a near-vertical series, the apicodorsal easily the longest and stoutest; without intercalary denticles or with a single denticle that arises from the dorsal surface of the apicoventral tooth. A single stout preapical tooth is present close to the apicodorsal tooth (see discussion below). Mandibles linear but short and stout, MI 18-28; in ventral view (and usually also in full-face view) the outer margin with a marked prebasal inflected angle.

Anterior clypeal margin broadly shallowly convex.

Scape stout, its leading edge with a series of crenellations or papillae from which long simple erect hairs arise; scape short, SI 59-67.

Apical antennomere not constricted basally.

Ventrolateral margin of head broadly concave in front of eye, the eye itself located on an acutely triangular projection of the margin that slopes outward and downward; apex of this projection extends beyond the eye and forms a sharp anteroventrally directed tooth or point below and beyond the midlength of the eye.

Propodeal teeth subtended by a narrow lamella.

Spongiform appendages of waist segments all present; lateral lobe of petiole small and posterior in profile.

Pilosity. Standing hairs everywhere simple, usually fine and soft, without bizarre pilosity. Pronotal humeral hair present, longer but not otherwise differentiated from the other main pilosity of the dorsal alitrunk. Dorsolateral margin of head with numerous freely laterally projecting hairs. First gastral tergite with filiform or flagellate hairs, such hairs also present on head and alitrunk. Hind tibia and basitarsus with long suberect to erect projecting hairs. Hairs on leading edge of scape long, suberect to almost erect.

Sculpture. Head reticulate-punctate; alitrunk variably sculptured. Disc of postpetiole mostly to entirely smooth. Gaster unsculptured except for basigastral costulae, the latter no longer than the maximum length of the postpetiole disc.

Notes

Interpretation of the mandibular apex is ambivalent. As described above, and at first glance, there appears to be a tridentate apical fork, of which the apicodorsal tooth is the largest, preceded on the inner margin by a single stout preapical tooth. On closer examination an alternative explanation of the apical fork morphology suggests itself. In this scenario there are two stout preapical teeth, the distal and larger of which has migrated to the mandibular apex where it has assumed the position of the apicodorsal tooth. The two teeth of the original apical fork have shifted downward and are now ventral to this new apicodorsal tooth. Of the two alternatives I suspect that the second is correct.

Two other species-groups in the region have strongly tridentate apical forks, the chapmani group and the trixodens group. In the latter the three teeth form a more or less vertical series and the apicomedian tooth appears to be a secondarily hypertrophied intercalary tooth that has become long and spiniform between the original apicodorsal and apicoventral fork teeth. In contrast the oblique tridentate fork of the chapmani-group, like that of the akalles-group, appears to have originated by the migration to the apex of an originally preapical tooth. However, unlike the akalles-group, Strumigenys chapmani and its relatives have no other preapical teeth.

The shape of the ventrolateral margin of the head in the vicinity of the eye is unique. Viewed obliquely from above the margin is extended laterally into an acutely triangular prominence. The eye is located on the dorsal surface of the prominence, close to its apex, but the apex itself projects beyond the outer margin of the eye as a small sharp tooth.

References

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