Comprehensive DescriptionRead full entry
Trachymyrmex dichrous HNS n. sp.
Worker (holotype). - Total length 5.0 (4.5-5.1) mm; head length 1.04 (0.99-1.07) mm; head width 0.99 (0.88-1.01) mm; maximum diameter of eyes 0.21 (0.17-0.22) mm; scape length 1.04 (0.93-1.07) mm; thorax length 1.65 (1.51-1.70) mm; petiole length 0.40 (0.35-0.40) mm; petiole width 0.24 mm; postpetiole length 0.38 (0.29-0.38) mm; postpetiole width 0.43 (0.40-0.43) mm; hind femur length 1.65 (1.49-1.70) mm. Head capsule black, rest of body medium brown, scapes and gaster with reddish hues. Long, yellowish brown, silky hairs abundant on head, thorax and pedicel, where they are recurved; same hairs, less recurved and more bristle-like on gaster, strictly oblique on scapes and legs. Dense pubescence of lighter color inclined or appressed on head, pedicel, gaster and appendages, erect or suberect on thorax, but never masking the integument.
Head as shown in Fig. 7. Mandibles smooth and shining except laterally on. base where they are finely striate; chewing border with approximately 9 teeth. Head capsule very finely granulate, opaque. Clypeus antero-mesially notched. Frontal lobes triangular, frontal carinae diverging caudad, fading out at posterior third of head. Front and vertex inconspicuously tuberculate, integument rough. Preocular carinae not curving mesad above eyes, but fading out somewhat behind eyes. Posterior half of antennal scrobe indistinct. Supraocular tumulus more or less vestigial; occipital corners likewise not prominent but rounded and edentate. Occiput in full-face view distinctly notched in the middle. No carinae on vertex. Inferior occipital corner indistinctly marginate and rounded. Inferior border of cheeks practically immarginate. Eyes moderately convex, more than 15 facets across greatest diameter. Scapes of antennae as long as head capsule, greatly surpassing occipital corner. All funicular segments decidedly longer than broad.
Thorax as shown in Fig. 8. Integument subopaque but sculpture indistinct. Hairs not arising from prominent tubercles. Pronotum with indistinct humeral angle, antero-inferior corner rounded, lateral teeth low, mesial teeth absent. Mesonotum with rather prominent anterior conical spines, facing obliquely laterad, followed by two pairs of small denticles, the posterior pair almost indistinct. Thorax constricted dorso-laterally at mesoepinotal junction, lacking a suture. Basal face of epinotum narrow, laterally indistinctly marginate; anteriorly indistinctly, posteriorly distinctly dentate; the latter representing the extremely short and inconspicuous epinotal spines. Epinotal stigma prominent. Femora thin, cylindrical, hind femora about as long as thorax.
Petiole and postpetiole as shown in Figs. 8 and 9. Piligerous tubercles prominent. Petiole pedunculate, node proper twice as broad as peduncle. Postpetiole flattened above, with a deep postero-median excision. Gaster opaque, with minute piligerous tubercles rather evenly distributed. Tergite I antero-laterally vestigially marginate.
Female and male unknown.
Specimens examined: 22 workers, as follows: Brasil, Goias State, Anapolis, January 7, 1966, W. W. Kempf leg. 16 workers (holotype and paratypes, WWK n. 4230); same locality but different nest, January 4, 1966, W. W. Kempf leg. 4 workers (paratypes, WWK n. 4199); Sao Paulo State, Agudos, December 13, 1955, W. W. Kempf leg. 1 worker (paratype, WWK n. 1493); Mato Grosso State: Chapada, May 1959, C. Amann leg. 1 worker (WWK, paratype).
Discussion. - Although highly distinctive, dichrous HNS belongs to the species-group which is characterized by smooth mandibles, by a more or less defined antennal scrobe, by rather straight preocular carinae that do not curve mesad above eyes, by the lack of a basal lobe on antennae. This group comprises by far the greatest number of species in the genus.
Within this group, dichrous HNS may at once be recognized by the ensemble of the following characters: triangular frontal lobes, lack of paired carinae on vertex, lack of an inferior occipital spine or tooth, lack of midpronotal teeth, lack of conspicuous tubercles on thorax, postero-dorsal border of postpetiole deeply excised. In addition, dichrous HNS has the antero-inferior angle of pronotum rounded, a character which is only found in isthmicus HNS and another still undescribed but otherwise completely different species. T. isthmicus HNS differs from dichrous HNS in the shape of the frontal lobes, the completely margined antennal scrobe, the presence of midpronotal teeth, the quadricarinate tergum I of the gaster. The same characters, plus the dentate antero-inferior pronotal corner, separate oetkeri HNS and urichi HNS , the closest sympatric species, from dichrous HNS .
The present species, which was found in Anapolis near km 46 of the Goiania highway, in a scrub-covered xerophilus woodland ("cerrado") by the gravel road leading to Leopoldo Bulhoes, at an altitude over 1000 m. The single nest entrance was surrounded by a sizeable crater of loosely heaped up earth crumbs. The lone stray worker from Agudos was taken from the ground in open and rather dry parkland. Hence it is probable that this species is a typical denizen of the vast "campos", that characterize the vegetation of central Brazil.