Tetramorium barbigerum

Known only from the type collection from Okombahe in Namibia.

Identification
Bolton (1980) - Within the solidum-complex of this group T. bargigerum is closest related to Tetramorium jordani, Tetramorium signatum and Tetramorium pogonion. It is easily separated from others in the complex as in Tetramorium grandinode the unique development of the petiole and postpetiole in that species renders it unmistakable, and it is unlikely to be confused with Tetramorium rufescens and Tetramorium glabratum as they are red in colour. T. solidum itself is isolated within the complex by possessing hairs on the dorsal alltrunk, which are absent in all other species.

Of the three that remain all have much coarser and denser cephalic sculpture than T. bargigerum with very conspicuous longitudinal costulae or sharp rugulae. Besides this T. jordani lacks propodeal spines, their place being taken by a pair of minute tubercles or merely by an angle; T. pogonion is smaller (HW 0.86-0.92) with relatively larger eyes (0.29-0.31 x HW), and in both T. pogonion and T. signatum the head does not narrow in front of the eyes.

Mbanyana et al (2018) - Tetramorium barbigerum is easily distinguished from all species of the Tetramorium solidum group by its head shape, which is narrower in front of the eyes than behind. Morphologically, this species is similar to Tetramorium jordani and Tetramorium signatum in that they are all black in colour and lack erect hairs on the mesosoma, but the sculpture in Tetramorium signatum is much stronger developed compared to T. jordani and T. barbigerum. Tetramorium barbigerum and T. jordani have a feeble cephalic sculpture, fading out at the level of the eyes and replaced by a fine superficial punctation. These two species can be easily distinguished from each other by the lack of propodeal spines/teeth in T. jordani (PSLI 1–2) and the presence thereof in T. barbigerum (PSLI 7–8).

Distribution based on Regional Taxon Lists
Afrotropical Region: Namibia.

Nomenclature

 *  barbigerum. Tetramorium barbigerum Bolton, 1980: 243, figs. 19, 20, 25 (w.) NAMIBIA.

Worker
Holotype: TL 5-1, HL 1:29, HW 1-24, CI 96, SL 0-92, SI. 74, PW 0-78, AL 1-32. Paratypes (20 measured): TL 4-8—5-4, HL 1:30-1:34, HW 1:24-1:30. CI 94-97, SL 0:91-0:95, SI 72-76, PW 0:74-0:86, AL 1-20-1-40. Maximum diameter of eye 0:30-0-33, about 0-24-0-26 x HW.

Mandibles longitudinally rugose. Anterior clypeal margin with a shallow median concavity or impression. Frontal carinae absent, the frontal lobes extended back to the level of the anterior cephalic hairs by an extremely faint raised line, ending in front of the level of the anterior margins of the eyes. Antennal scrobes absent. Maximum diameter of eye c. 0:32, about 0-24 x HW. With the head in full-face view the occipital margin shallowly concave, the corners convex and broadly rounded. Head narrowing in front of eyes, the width directly behind them (HW) 1-24, immediately in front of them 1-17. Propodeal spines in profile short, thorn-like, slightly longer than their basal width,. Metapleural lobes narrow, evenly rounded, low. Petiole in profile strongly nodiform, in dorsal view broader than long, broadest posteriorly and with the anterior face convex, rounding into the lateral margins. Postpetiole broader than long in dorsal view, the sides rounded, broader than the petiole (maximum width of petiole node dorsally 0-37, of postpetiole 0-47). Dorsum of head with fine, scattered longitudinal costulae or faint rugulae, the spaces between them weakly punctulate or shagreened. The costulate part of the sculpture strongest behind the posterior clypeal margin, fading out posteriorly so that on the occiput only the slightest vestiges of longitudinal sculpture remain, the punctulate component conspicuous. Sides of head above and behind eyes and sides of occipital lobes predominantly punctulate-shagreened. Dorsal alitrunk uniformly very finely reticulate-punctulate, the punctures very tightly packed and appearing shagreened in places. Vestigial traces of costulae may be seen in places, especially on the pronotum. Dorsal surfaces of petiole and postpetiole very feebly shagreened, shining in patches. Base of first gastral tergite with vestigial shagreening which is almost effaced. Erect hairs absent from dorsal alitrunk, petiole, postpetiole and first gastral tergite, present on clypeus, gastral segments behind the first and on the first sternite. Dorsum of head behind clypeus with two pairs of hairs, the first situated between the levels of the posterior margins of the antennal fossae and the anterior margins of the eyes, the second located close to the occipital corners. Ventral surface of head with a strongly developed psammophore. Hind tibiae with appressed long pubescence. Colour uniform blackish brown, the appendages somewhat lighter.

Paratypes: Conforming to description of holotype but in a few specimens the impression of the anterior clypeal margin slightly more strongly or more weakly developed. The erect hairs on the cephalic dorsum are easily lost by abrasion and one or two are missing in some of the paratypes. Colour not particularly variable but a few paratypes black.

Mbanyana et al. (2018) - (workers N = 6) HL 1.214–1.266(1.244); HW 1.201–1.240 (1.223) SL 0.827–0.891 (0.857); EL 0.297–0.323 (0.308); PH 0.570–0.590 (0.583); PW 0.747–0.806 (0.775); WL 1.227–1.356 (1.294); PSL 0.089–0.098 (0.093); PTH 0.354–0.374 (0.363); PTL 0.354–0.384 (0.370); PTW 0.364–0.384 (0.375); PPH 0.517–0.568 (0.536); PPL 0.295–0.403 (0.362); PPW 0.443–0.472 (0.462); OI 24–26 (25); CI 95–101 (98); SI 67–72 (70); DMI 56–62 (60); LMI 42–49 (45); PSLI 7–8 (8); PeNI 46–50 (48); LPeI 95–108 (102) DPeI 108–132 (101); PpNI 58–62 (60); LPpI 57–76 (68); DPpI 117–153 (129); PPI 118–127 (123).

Type Material
Holotype worker, South West Africa: 10 miles [16 km] W. of Okombahe, 920 m, 10.v.1958 (R. E. Ross & R. E. Leech). Paratypes. Thirty-seven workers with same data as holotype (CASC; ; ; ).

Mbanyana et al. (2018) examined - Holotype. Namibia: worker, 10 mi. (16 km) W of Okombahe, 920 m a.s.l., 10 May 1958, R.E. Ross and R.E. Leech leg. (: CASTYPE13386). Paratypes. Namibia: 17 pinned workers, same data as holotype (CASC: CASENT0270787 to CASENT0270792); 3 pinned workers, same data as holotype.

References based on Global Ant Biodiversity Informatics

 * Bolton B. 1980. The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Ethiopian zoogeographical region. Bulletin of the British Museum (Natural History). Entomology 40: 193-384.
 * Mbanyana N. 2013. Taxonomy, phylogeny and biogeography of seed-harvesting ants in the Tetramorium solidum-group (Hymenoptera: Formicidae). Masters of Science in the Department of Botany and Zoology at Stellenbosch University 115 pages.
 * Mbanyana N., F. Hita Garcia, H. G. Robertson, and J. J. Le Roux. 2018. A taxonomic revision of seed harvester ants of the Tetramorium solidum group (Hymenoptera: Formicidae) in southern Africa. European Journal of Taxonomy 454: 1-59.