Octostruma obtusidens

Octostruma obtusidens is a moderately abundant lowland species. All Central American records are from sea level to 800 m. It occurs in mature to highly disturbed rainforest and in seasonal moist forest. Most collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. In quantitative 1 m2 litter plot samples, it can occur in up to 11% of samples. Dealate queens are occasionally found together with workers in litter samples. One nest was observed at La Selva Biological Station in Costa Rica. A colony occurred in a 2–3 cm diameter nest in a soil cavity beneath a rotting palm trunk. The colony was polygynous, with at least 4 dealate queens. The nest contained an egg of Phasmatodea. (Longino 2013)

Identification
Face lacking transverse arcuate carina; basal five teeth of mandible bluntly rounded; face sculpture foveolate with at most faint longitudinal rugulae (longitudinally rugose on Octostruma excertirugis); ground pilosity curved, projecting from surface; first gastral tergite punctate over entire surface (punctate on anterior half, fading to nearly smooth and shining posteriorly on O. excertirugis). (Longino 2013)

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

Nomenclature

 *  obtusidens. Octostruma obtusidens Longino, 2013: 44, figs. 1F, 3E, 4, 5F, 10B, 12A, 14E, 33, 43 (w.q.) COSTA RICA.

Worker
HW 0.67-0.74, HL 0.62-0.64, WL 0.76-0.80, CI 104-116 (N=6). Labrum wider than long, strap-like lateral portions converging from base to near apex, joined by thin translucent cuticle medially but leaving distinctly bilobed apex, with distinct median notch; mandible triangular, in profile view with mandible closed, in same plane as clypeus, apex of mandible not down-turned; mandible with 8 teeth, tooth 1 continuous with basal rim of dorsal surface, teeth 1–5 bluntly rounded, similar in shape, a denticle between 4 and 5, teeth 6–7 smaller, not as blunt, tooth 8 long and acute; masticatory margin evenly curved, with no development of downturned apical fork; dorsal surface of mandible smooth and shining; ventral surface rounding into dorsal surface; scape flattened, with pronounced anterobasal lobe, dorsal surface roughened, microfoveolate; clypeus with broad, shallow emargination anteriorly; clypeal dorsum convex medially, clypeal suture impressed, forming shallow trough between clypeus and frons; clypeus and face densely foveolate, overlain with faint irregular rugulae; frontal carinae faint, nearly obsolete; antennal socket deep, dorsal rim of socket continuous with pronounced dorsal margin of antennal scrobe; antennal scrobe deep, pocket-like, strongly delimited dorsally, posteriorly, and ventrally with sharply defined laminar cuticular rim; compound eye small, circular, composed of about 7 ommatidia; feeble carina extends from ventral margin of antennal socket across floor of scrobe to compound eye; scrobe foveolate; occipital carina extends a short distance onto ventral surface of head, fading at level of compound eye; undersurface of head foveolate.

Promesonotum and dorsal face of propodeum forming an even convexity in profile, promesonotal suture not impressed, promesonotum with broad, weak, longitudinal impression; metanotal groove not impressed; propodeum with distinct dorsal and posterior faces meeting at a broadly obtuse angle; propodeal spines well-developed, acute, laterally flattened, internal surface concave, with dorsal margin of spine forming carina that curves medially but does not extend to midline, spine extending ventrally as thin infradental carina; irregular rugulae extend between propodeal spines, faint to absent medially, weakly separating dorsal and posterior faces of propodeum; propodeal spiracle large, diameter similar to width of base of propodeal spine, located below propodeal spine and abutting posterior margin; dorsum of promesonotum foveolate, overlain with weak rugulae; side of mesosoma and dorsal face of propodeum foveolate; posterior face of propodeum smooth, sublucid.

Petiole in profile with peduncle differentiated from node, node with differentiated anterior face; node subquadrate, with long sloping dorsal face and short vertical posterior face; anteroventral margin with pronounced, anteriorly-directed peg-like tooth; postpetiole low, broad, crescent-shaped in dorsal view; dorsum of petiolar node and postpetiole foveolate; first gastral tergite and sternite densely punctate.

Anterior labral lobe with radiating tuft of soft, thick, translucent, capitate setae of unequal length projecting from apex; each larger mandibular tooth with fully appressed seta running length of tooth; dorsal surface of scape, clypeus, face, promesonotal dorsum, legs, dorsal petiolar node, dorsal postpetiole, and first gastral tergite covered with conspicuous ground pilosity of small clavate setae that are strongly curved and projecting from the surface (not appressed), ground pilosity absent from side of mesosoma, dorsal and posterior propodeum; larger erect, brush-like spatulate setae conspicuous, anterior margin of scape with about 10, face with about 12, promesonotum with 4, apex of mesotibia with 5, petiolar node with 2, postpetiole with 2, first gastral tergite with 16 evenly distributed on tergite, first gastral sternite with 15–20 smaller clavate setae, more clustered posteriorly and medially.

Color orange.

Queen
HW 0.72–0.78, HL 0.68–0.71, WL 0.96–0.99, CI 102–113 (n=3). Mandible smooth and shiny; clypeus and face irregularly rugose, rugae somewhat longitudinally oriented on frons; antennal scrobe foveolate; ocelli distinct; compound eye large, multifaceted, about 12 ommatidia in longest row.

Mesosoma with queen-typical alar sclerites; anterior pronotum shallowly foveolate rugulose, lateral pronotum foveolate; mesoscutum and scutellum with weak foveolation overlain with prominent longitudinal rugulae; mesopleuron, metapleuron, and side of propodeum punctate; transverse mesopleural sulcus prominent, delimited above and below with a distinct carina; transverse metapleural sulcus delimited with an elliptical carina; dorsal face of propodeum foveolate rugulose, posterior face smooth; propodeal spines similar to worker; first gastral tergite and sternite punctate.

Ground pilosity thin and sparse, not clavate like worker; erect setae long and clavate, not spatulate and brush-like; face with about 22 erect setae, pronotum with 5–8, mesoscutum with 10–12, axilla with 1, scutellum with 2, metanotum with 2, petiolar node with 2, postpetiole with 6, first gastral tergite with 35–40.

Color orange to red orange, ocellar triangle darker brown.

Type Material
Holotype worker: COSTA RICA, Heredia: La Selva Biological Station, 10.43333, -84.01667, ±2 km, 50 m, 16 Mar 1993, wet forest, nest under dead wood (J. Longino#3390), unique specimen identifier CASENT0629827. Paratype workers, queen: same data, CASENT0627385; CASC, CASENT0629813; , CASENT0629814; , CASENT0629815; , CASENT0629816; , CASENT0629817; , CASENT0629818; , CASENT0629819; , CASENT0629820; CASC, CASENT0629821; CASC, CASENT0629822; CASC, CASENT0629823; CASC, CASENT0629824; CASC, CASENT0629825; , CASENT0629826.

Etymology
The name refers to the blunt teeth on the mandible. It is a noun in apposition and thus invariant.

References based on Global Ant Biodiversity Informatics

 * 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.