Octostruma stenognatha

The type was collected "in soil cover berlesate from very moist forest".

Identification
Octostruma stenognatha, Octostruma batesi, and Octostruma betschi are all similar in size and head shape and possibly form a clade. Although geographic coverage is poor, the known specimens form an allopatric or parapatric replacement series in South America. (Longino 2013)

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil.

Nomenclature

 *  stenognatha. Octostruma stenognatha Brown & Kempf, 1960: 196, figs. 25, 28 (w.q.) BRAZIL.

Worker
Holotype. TL 2.2, HL 0.52, HW 0.52 (CI 100), WL 0.56 mm. Paratype workers: TL 2.0-2.3, HL 0.49-0.56, HW 0.49-0.56 (CI 94-103), WL 0.52-0.60 mm, based on 33 workers from at least 14 different nest series from 4 different localities in all parts of the known range. Paratypes, ergatoid females (or gynecoid workers): TL 2.6-2.8, HL 0.58-0.60, HW 0.60-0.63 (CI 100-106), WL 0.65-0.71 mm, based on 4 examples.

The holotype, paratypes and ergatoids are very similar to the corresponding castes of Octostruma balzani, but the head averages narrower and differs slightly but significantly in form. Sides of head in the region of the eyes less strongly converging and longer; distance between anteocular and postocular angles normally exceeding distance between postocular and occipital angles (usually the postocular angle — occipital angle distance is slightly greater in balzani). Dorsum of head gently convex, with a shallow median impression centered on the vertex (dorsum not divided into convex occipital and flat or concave frontal surfaces as it is in balzani).

Mandibles narrower than in balzani, with nearly or quite straight outer margins; basal tooth subtriangular, pointed, its basal border sloping sharply away to the basal margin of the mandible in such a way as to leave a gap in front of the clypeus at full closure (though the gap may be hard to see if the labrum is extended beneath it). Masticatory margin with 7 triangular teeth plus 1-3 minute intercalary denticles. Basal lobe of scape more broadly rounded (less produced) than in balzani.

Alitrunk and remainder of body formed much as in balzani, but petiolar node not so strongly compressed anteroposteriorly, its dorsum only slightly broader than long and about half as wide as postpetiole.

Ground pilosity even less well-developed than in the average balzani worker. Erect clavate-spatulate hairs more abundant and longer than in average balzani workers, but not exceeding the maximum number for that species; usually 16-18 erect hairs on cephalic dorsum, of which the hair nearest the eye is placed slightly in front of the eye (more mesad of eye in balzani). The postpetiole carries 4 hairs along the posterior margin, of which the outer pair is placed on the posterolateral angles. Alitrunk with 1 or 2 pairs, petiolar node with a single pair.

Color and sculpture as in balzani, except that the interpunctural spaces on the gastric dorsum seem to be smoother and more shining than the average for balzani.

The ergatoids have slightly coarser sculpture and more erect hairs than the worker has; eyes much larger than in worker; ocelli small, forming an obtuse triangle; petiolar node more transverse.

Queen
Dealate paratype: TL 2.7, HL 0.58, HW 0.58 (CI 100), WL 0.78 mm. With true pterothorax and other modifications of its caste; erect hairs more abundant than in ergatoid or worker.



Type Material
Longino (2013) - Holotype worker: Brazil, São Paulo, Agudos, 23 Jan 1955, in soil cover berlesate from very moist forest (W. W. Kempf, No. 1334) (not examined). Paratype workers, worker intercastes: same data as holotype; São Paulo, Cantareira, 1 Mar 1959 (Kempf & Santos); Rio de Janeiro, Itatiaia (J. F. Zikán, Coll. Borgmeier); Santa Catarina, Nova Teutonia, 27° 11' S, 52° 23' W, Aug 1952 (F. Plaumann) ] (examined). Paratype queen not examined.

References based on Global Ant Biodiversity Informatics

 * Brown W. L., Jr., and W. W. Kempf. 1960. A world revision of the ant tribe Basicerotini. Stud. Entomol. (n.s.) 3: 161-250.
 * Calixto J. M. 2013. Lista preliminar das especies de formigas (Hymenoptera: Formicidae) do estado do Parana, Brasil. Universidad Federal do Parana 34 pages.
 * 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.
 * Feitosa R. dos S. M. and A. S. Ribeiro. 2005. Mirmecofauna (Hymenoptera, Formicidae) de serapilheira de uma área de Floresta Atlântica no Parque Estadual daCantareira  São Paulo, Brasil. Biotemas 18: 51-71.
 * Fleck M. D., E. Bisognin Cantarelli, and F. Granzotto. 2015. Register of new species of ants (Hymenoptera: Formicidae) in Rio Grande do Sul state. Ciencia Florestal, Santa Maria 25(2): 491-499.
 * Kempf W. W. 1961. Nota preliminar sôbre a fauna das formigas de Agudos, S. P. (Hymenoptera: Formicidae). Revista Brasileira de Entomologia 10: 205-208.
 * Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
 * Longino J. T. 2013. A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae). Zootaxa 3699(1): 1-61.
 * Pacheco, R., R.R. Silva, M.S. de C. Morini, C.R.F. Brandao. 2009. A Comparison of the Leaf-Litter Ant Fauna in a Secondary Atlantic Forest with an Adjacent Pine Plantation in Southeastern Brazil. Neotropical Entomology 38(1):055-065
 * Resende J. J., G. M. de M. Santos, I. C. do Nascimento, J. H. C. Delabie, and E. M. da Silva. 2011. Communities of ants (Hymenoptera  Formicidae) in different Atlantic rain forest phytophysionomies. Sociobiology 58(3): 779-799.
 * Rosa da Silva R. 1999. Formigas (Hymenoptera: Formicidae) do oeste de Santa Catarina: historico das coletas e lista atualizada das especies do Estado de Santa Catarina. Biotemas 12(2): 75-100.
 * Rosa da Silva R., and B. Cortes Lopes. 1997. Ants (Hymenoptera: Formicidae) from Atlantic rainforest at Santa Catarina Island, Brazil: two years of sampling. Rev. Biol. Trop. 45(4): 1641-1648.
 * Silva R. R., R. S. Machado Feitosa, and F. Eberhardt. 2007. Reduced ant diversity along a habitat regeneration gradient in the southern Brazilian Atlantic Forest. Forest Ecology and Management 240: 61-69.
 * Silva R.R., and C. R. F. Brandao. 2014. Ecosystem-Wide Morphological Structure of Leaf-Litter Ant Communities along a Tropical Latitudinal Gradient. PLoSONE 9(3): e93049. doi:10.1371/journal.pone.0093049
 * Silvestre R., M. F. Demetrio, and J. H. C. Delabie. 2012. Community Structure of Leaf-Litter Ants in a Neotropical Dry Forest: A Biogeographic Approach to Explain Betadiversity. Psyche doi:10.1155/2012/306925
 * Siqueira de Castro F., A. B. Gontijo, W. Duarte da Rocha, and S. Pontes Ribeiro. 2011. As comunidades de formigas de serapilheira nas florestas semidecíduas do Parque Estadual do Rio Doce, Minas Gerais. MG.BIOTA, Belo Horizonte 3(5): 5-24.
 * Stroher P. R., A. L. S. Meyer, E. Zarza, W. L. E. Tsai, J. E. McCormack, and M. R. Pie. 2019. Phylogeography of ants from the Brazilian Atlantic Forest. Organisms Diversity & Evolution https://doi.org/10.1007/s13127-019-00409-z
 * Suguituru S. S., D. R. de Souza, C. de Bortoli Munhae, R. Pacheco, and M. S. de Castro Morini. 2011. Diversidade e riqueza de formigas (Hymenoptera: Formicidae) em remanescentes de Mata Atlântica na Bacia Hidrográfica do Alto Tietê, SP. Biota Neotrop. 13(2): 141-152.
 * 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
 * Suguituru S. S., R. Rosa Silva, D. R. de Souza, C. de Bortoli Munhae, and M. Santina de Castro Morini. Ant community richness and composition across a gradient from Eucalyptus plantations to secondary Atlantic Forest. Biota Neotrop. 11(1): 369-376.
 * Ulyssea M.A., C. E. Cereto, F. B. Rosumek, R. R. Silva, and B. C. Lopes. 2011. Updated list of ant species (Hymenoptera, Formicidae) recorded in Santa Catarina State, southern Brazil, with a discussion of research advances and priorities. Revista Brasileira de Entomologia 55(4): 603-611.
 * da Silva R. R., and R. Silvestre. 2000. Diversidade de formigas (Hymenoptera: Formicidae) em Seara, oeste de Santa Catarina. Biotemas 13(2): 85-105.
 * da Silva, R.R. and R. Silvestre. 2004. Riqueza da fauna de formigas (Hymenoptera: Formicidae) que habita as camadas superficiais do solo em Seara, Santa Catarina. Papéis Avulsos de Zoologia (São Paulo) 44(1): 1-11