Acanthostichus quadratus

The type material was found in the stomach of a toad (Bufo crucifer).

Identification
A member of the serratulus species complex. 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.

Type Material
Worker, female, BOLIVIA: Misiones de Mosetenes, Rio Beni [seen]. Acanthostichus quadratus, lectotype worker ({MCSN) and paralectotype subdichthadiiform female (MCSN) (here designated); Amazonas, Staudinger and (followed by illegible name]; Acanthostichus quadratus Em.; Typus (MCSN) [all seen]; Acanthostichus serratulus var. niger, lectotype (here designated) and 1 paralectotype, both workers. Est[acion] Exp[erimental] Loreto (Misiones – Arg[entina]). Dr. A. A. Oglobin. # 1940. TIPUS. Acanthostichus serratulus Sm. V. niger Snts. [both seen].

References based on Global Ant Biodiversity Informatics

 * Brandao, C.R.F. 1991. Adendos ao catalogo abreviado das formigas da regiao neotropical (Hymenoptera: Formicidae). Rev. Bras. Entomol. 35: 319-412.
 * Cuezzo, F. 1998. Formicidae. Chapter 42 in Morrone J.J., and S. Coscaron (dirs) Biodiversidad de artropodos argentinos: una perspectiva biotaxonomica Ediciones Sur, La Plata. Pages 452-462.
 * Emery C. 1895. Die Gattung Dorylus Fab. und die systematische Eintheilung der Formiciden. Zoologische Jahrbücher. Abteilung für Systematik, Geographie und Biologie der Tiere 8: 685-778.
 * Emery C. 1911. Hymenoptera. Fam. Formicidae. Subfam. Ponerinae. Genera Insectorum 118: 1-125.
 * Favretto M. A., E. Bortolon dos Santos, and C. J. Geuster. 2013. Entomofauna from West of Santa Catarina State, South of Brazil. EntomoBrasilis 6 (1): 42-63.
 * Fernández, F. and S. Sendoya. 2004. Lista de las hormigas neotropicales. Biota Colombiana Volume 5, Number 1.
 * Figueiredo C. J. de, R. R. da Silva, C. de Bortoli Munhae, and M. S. de Castro Morini. 2013. Ant fauna (Hymenoptera: Formicidae) attracted to underground traps in Atlantic Forest. Biota Neotrop 13(1):  176-182
 * Forel A. 1906. Fourmis néotropiques nouvelles ou peu connues. Annales de la Société Entomologique de Belgique 50: 225-249.
 * Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
 * Kusnezov N. 1962. El género Acanthostichus Mayr (Hymenoptera, Formicidae). Acta Zoologica Lilloana 18: 121-138.
 * MacKay W. P. 1996. A revision of the ant genus Acanthostichus (Hymenoptera: Formicidae). Sociobiology 27: 129-179
 * Medeiros Macedo L. P., E. B. Filho, amd J. H. C. Delabie. 2011. Epigean ant communities in Atlantic Forest remnants of São Paulo: a comparative study using the guild concept. Revista Brasileira de Entomologia 55(1): 7578.
 * Morini M. S. de C., M. Yashima, F. Y. Zene, R. R. da Silva, and B. Jahyny. 2004. Observations on the Acanthostichus quadratus (Hymenoptera: Formicidae: Cerapachyinae) visiting underground bait and fruits of the Syagrus romanzoffiana, in an area of the Atlantic forest, Brazil. Sociobiology 43(3): 573-578.
 * Santschi F. 1933. Fourmis de la République Argentine en particulier du territoire de Misiones. Anales de la Sociedad Cientifica Argentina. 116: 105-124.
 * Suguituru S. S., M. Santina de Castro Morini, R. M. Feitosa, and R. Rosa da Silva. 2015. Formigas do Alto Tiete. Canal 6 Editora 458 pages
 * Vittar, F. 2008. Hormigas (Hymenoptera: Formicidae) de la Mesopotamia Argentina. INSUGEO Miscelania 17(2):447-466