Octostruma gymnogon

Octostruma gymnogon is a montane species. It occurs mostly in mature cloud forest. On the Barva Transect in Costa Rica it shows a sharp elevationally parapatric distribution with Octostruma amrishi and is restricted to elevations above 400 m. Almost all collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. Dealate queens and intercaste workers occasionally occur together with workers in litter samples. Additional comments are included under Octostruma balzani. (Longmino 2013)

Identification
Longino (2013) - Mandible with 8 teeth, tooth 1 a broad blunt lamella, strongly differentiated from tooth 2, teeth 2–5 acute, similar in shape, with denticles between them; teeth 5–8 forming an apical fork, with 5 and 8 large, 6 and 7 small partially confluent denticles (O. balzani complex); face setation, lacking erect setae on posterolateral margins of head (present in Octostruma balzani, Octostruma megabalzani, and Octostruma trithrix) and on the posteromedian margin (present in Octostruma amrishi); mesosomal dorsum lacking a pair of erect setae (present in O. balzani, O. megabalzani, and O. trithrix); metanotal groove not impressed in profile view (impressed in O. balzani and O. megabalzani).

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica, Guatemala, Honduras, Nicaragua, Panama.

Nomenclature

 *  gymnogon. Octostruma gymnogon Longino, 2013: 33, figs. 1E, 3D, 5D, 24, 42 (w.q.) COSTA RICA.

Worker
HW 0.62–0.68, HL 0.56–0.59, WL 0.62–0.68, CI 109–114 (n=6). Matching in almost every respect the description for O. balzani, except the differences outlined in the Diagnosis and key. Octostruma gymnogon is generally darker brown than either O. amrishi or O. balzani.

Queen
HW 0.66, HL 0.60, WL 0.79, CI 110 (n=1). Similar in all respects to Octostruma balzani.

Type Material
Holotype worker: COSTA RICA, Alajuela: Casa Eladio, Rio Peñas Blancas, 10.31667, -84.71667, ±2 km, 800 m, 26 Apr 1987, primary wet forest, sifted leaf litter (J. Longino#1579-s), unique specimen identifier CASENT0627379]. Paratype workers, queen: same data INBC, CASENT0627380; same data except (J. Longino#1578-s), ENT 143374; , LACM ENT 143375; 27 Apr 1988 (J. Longino#2015-s) , LACM ENT 143379; , LACM ENT 143380]; 10 May 1989 (J. Longino#2529-s) , INBIOCRI001281404; , INBIOCRI001281422; 23 May 1990 (J. Longino#2701-s) , INBIOCRI001282517; 2 Mar 2004 (J. Longino#5278-s) CASC, JTLC000005383; , JTLC000005390.

Etymology
The name refers to the lack of a spatulate seta on the posterolateral vertex margin. It is a noun in apposition and thus invariant.

References based on Global Ant Biodiversity Informatics

 * Longino J. T. 2013. A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae). Zootaxa 3699(1): 1-61.
 * Longino J. T. L., and M. G. Branstetter. 2018. The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants. Ecography 41: 1-12.
 * Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/