Acanthostichus quadratus

Identification
Mackay (1996) - This species is closely related to Acanthostichus serratulus, but differs in the quadrate petiole (elongate in A. serratulus). It is similar to Acanthostichus kirbyi, but differs in that the clypeus is relatively wider (Fig. 13) and the two lateral teeth on the clypeus are almost always absent.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Bolivia, Brazil, Ecuador, Peru.

Nomenclature

 *  quadratus. Acanthostichus quadratus Emery, 1895j: 750, fig. OO.A; pl. 16, figs. 5, 6; pl. 17, fig. 12 (w.q.) BOLIVIA. Senior synonym of niger: Mackay, 1996: 162.
 * niger. Acanthostichus serratulus var. niger Santschi, 1933e: 105 (q.) ARGENTINA. Junior synonym of serratulus: Kusnezov, 1962a: 132. Revived from synonymy and raised to species: Brown, 1975: 42. Junior synonym of quadratus: Mackay, 1996: 162.

Mackay (1996):

Worker
HL 0.99-1.49, HL 0.88-1.46, SL 0.49-0.78, SW 0.19-0.24, WL 1.18-1.91, PW 0.40-0.73, PL 0.41-0.83, FL 0.68-0.94, FW 0.23-0.38, SI 49-52, CI 89-99, PI 93-120, FI 2.50-3.14, SL/SW 2.60-3.06.

Median and lateral clypeal teeth poorly developed (usually absent, except in larger workers); head slightly convex posteriorly; petiole subquadrate, subpetiolar process with posteriorly directed tooth; dorsum of petiole usually moderately smooth and shining with longitudinal troughs, especially well developed near the lateral borders.

Queen
The types of A. serratulus var. niger are identical to those of A. quadratus. My concept of the female is based on a paralectotype A. serratulus var. niger mounted on a piece of card next to the lectotype worker.

HL 1.83, HW 2.10, SL 0.79, SW 0.30, EL 0.23, WL 2.63, PW 1.85, PL 0.96, FL 1.35, FW 0.50, SI 43, CI 115, PI 52, FI 2.70, SL/SW 2.63. Subdichthadiiform (Fig. 50); mandibles without teeth (except apex); frontal carinae widely separated; eyes large; malar groove apparently absent; eyes large; ocelli absent; occiput slightly concave; dorsum of mesosoma with promesonotal suture poorly developed, metanotal suture somewhat more developed; propodeal angles in form of epilaut-like carinae; petiole much wider than long (Fig. 52); posterior femur not incrassate. Mostly smooth and shining throughout, with few scattered punctures, except sides of mesosoma and petiole, (which are more heavily and deeply punctate with a few longitudinal striae), and postpetiole and gaster (which are densely and evenly punctate). Long, flexuous hairs on all surfaces, gaster with dense, short, erect pubescence. Concolorous medium brown to dark reddish brown.