Odontomachus biumbonatus

Identification
Key to Odontomachus of the New World

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil, Ecuador, French Guiana, Guyana, Peru, Suriname.

Nomenclature

 *  biumbonatus. Odontomachus biumbonatus Brown, 1976a: 131, fig. 22, pl. 1B (w.q.) ECUADOR.

Worker
Holotype: TL 13.6, HL 3.66, HW (across vertex) 2.50, HW (across ocular prominences) 2.76, ML 1 .90, scape L 2.96, eye L 0.48, WL 3.76 mm; CI 68, MI 52, SI 118.

Paratypes (smallest worker, Rio Taruma, Amazonas): TL 10.3, HL 2.78, HW (vertex) 1.80, HW (ocular prominences) 2.08, ML 1.56, scape L 2.50, eye L 0.38, WL 3.00 mm; CI 65, MI 56, SI 139.

Holotype and 4 worker paratypes from 4 localities, including those with largest and smallest heads: TL 10.3-13.6, HL 2.78-3.72, HW (vertex) 1.80-2.50, ML 1.56-1.92, WL 3.00-3.76, SL 2.50-3.00 mm; CI 65-68, MI 52-56, SI 118-139, ex 36 paratypes from 9 localities.

Head and mandibles massive, form as in Odontomachus laticeps, vertex notably wider than trunk and gaster. Callows with finely serrate inner (ventral) mandibular borders and three stout sharp-edged teeth at apex, the basal most of these of these subrectangular and with 1-2 smaller supplementary points on proximal edge. Older specimens (most foraging workers) with the apical teeth more or less worn down to rounded stumps. Palpi segmented 4, 3. Striation of head complete on dorsum, moderately fine (6-7 striae per 0.1 mm sample square on middle of left half of vertex), extending nearly halfway down sides, shining. Antennal fossae and sides of head smooth and shining, usually bluish-opalescent. Mandibles nearly smooth above, shining, with a few coarse punctures. Outer borders of mandibles, like antennae, densely punctate, weakly shining, with dense appressed to decumbent pubescence. Scapes slightly surpassing posterior margins of head when held back. Cervical cavity and underside of head smooth and shining.

Trunk robust; metanotum developed as a depressed transverse band, separated from mesonotum by a narrow depression with short longitudinal rugae. Propodeum weakly convex in profile over anterior half, followed by a shallow concavity of variable extent. Anterior propodeal convexity usually weakly longitudinally sulcate as seen from above. Declivity short and moderately convex.

Pronotum finely striate in very varied patterns: whorled, longitudinal, oblique, or transverse, but normally with at least some transverse striation forming a posterior band; mesonotum and propodeum transversely striate, the striae coarser on propodeal declivity. Mesopleura smooth and shining, except for anterior and posteroventral ends, which have variable striation; smooth part often bluish opalescent.

Head in center of vertex with a pair of long, anteriorly inclined hairs (L 0.04-0.05 mm), and sometimes in front of these a few shorter decumbent to suberect hairs. Long oblique hairs also present on undersides of mandibles, anterior underside of head (a few very short, delicate erect hairs here also ), and coxae, trochanters and basal half of undersides of femora. Pronotum with a group of 4-10 coarse, curved erect hairs, mostly 0.05-0.06 mm. long.

Pubescence on head moderately abundant but spaced, decumbent to appressed, crossing the striation in most places, and therefore easily seen at a magnification of 20x. On trunk, pubescence inconspicuous, more restricted, dilute, mostly directed caudad and appressed. Legs shining, finely punctulate and with dense, short decumbent pubescence, except posterior (mesial) surfaces of femora, which are smooth and shining.

Petiolar node shape as in fig. 22; the characteristic abruptly rooted apical spine is slender, acute and nearly erect, i.e., on or near the major axis of the node, and may even be tilted slightly cephalad. Posterior face of node vertically sulcate ; sulcus flanked near mid-height by a pair of low swellings, best seen in oblique posterolateral view, from which the species takes its name. Node shining, smooth or nearly so on all surfaces above the alutaceous basal part, with scattered punctures; fine decumbent pubescence directed upward on anterior face and sides.

First gastric tergum glassy smooth, often with bluish reflections, with scattered coarse punctures from which arise numerous tapered, -fine, yellowish hairs, subdecumbent to suberect, about 0.15 to 0.55 (mostly 0.3-0.4 mm.) long. Pubescence long (0.12-0.15 mm.) and fine, appressed to decumbent, conspicuous but not crowded, the separated hairs only rarely touching one another (Plate I, B). Remaining segments of gaster also shining, with a partly feeble alutaceous sculpture varying to smooth and shining, with punctures. In some samples, especially from Para and Amazonian Peru, even the disc and posterior part of the first gastric tergum may have a very faint microreticulum visible in good light at magnifications of about 40x or more, but this does not interfere with the shininess of the integument of this segment. All segments of gaster, both above and below, with numerous hairs and sparse pubescence like the first tergum.

Body color in mature workers dark reddish-brown to piceous, often appearing black or nearly so to the naked eye. Mandibles, antennae and legs usually a little lighter, castaneous.