Eurhopalothrix xibalba

This species occurs in mature wet forest across a broad range of elevations, from near sea level to nearly 1700 m elevation. All known collections are from Winkler or Berlese samples of sifted leaf litter and rotten wood. At low-elevation sites it is always low density, occurring in < 1% of quantitative miniWinkler samples. At two mid-elevation sites it occurred at higher densities: 9% at a 1500 m site on the Barva Transect in Costa Rica, and 18% at 1120 m in Parque Nacional Azul Meambar in Honduras. (Longino 2013)

Identification
Masticatory margin of mandible with double row of teeth, outer series of lower triangular teeth, inner row of 3 long, spiniform teeth; erect setae on face strongly spatulate; basal lobe of scape strongly developed, SLI 21–25; HW 0.57–0.66. Similar to Eurhopalothrix gravis, Eurhopalothrix hunhau. (Longino 2013)

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

Nomenclature

 *  xibalba. Eurhopalothrix xibalba Longino, 2013: 144, figs. 2G, 7B, 10A, 33, 36 (w.) COSTA RICA.

Worker
HW 0.57–0.66, HL 0.56–0.64, SL 0.36–0.40, SLL 0.08–0.10, CI 101–105, SLI 22–25 (n=10). Labrum longer than broad, anterolateral gibbosities of basal portion developed as short, sharp, ventrally-directed teeth, apical portion of labrum elongate, in approximately same plane as basal portion (not flexed dorsally), distinctly bilobed with elongate, bluntly triangular lobes; lobes with fringe of translucent setae, apical setae capitate; mandible triangular, dorsal surface convex, roughened, dull, rounding into ventral surface; interior surface concave, smooth and shining; masticatory margin with two tooth rows, an outer row of 10 teeth and an inner row of 3 long needle-shaped teeth, behind outer teeth 3–6 and projecting beyond them, nearly 2x length of flanking outer teeth; tooth 1 of outer row broader than others, low, blunt; tooth 2 long and acute; teeth 3–6 low, blunt; teeth 7 and 10 long and sharp, similar to teeth of inner row; teeth 8–9 shorter; scape with strongly developed basal lobe; scrobe deep, sharply delimited dorsally and ventrally, abutting deep antennal socket; surface of scrobe smooth; eye small, comprising 4–5 partially fused ommatidia; clypeus convex posteromedially, sloping to slightly concave anterior apron, anterior margin with broad, semicircular emargination; surface superficially roughened; juncture of clypeus and frons a shallow transverse trough, continuing to sides of head (frontal lobes convex like medial clypeus); sides of head above eyes strongly angulate; surface of face posterior to clypeofrontal trough uniformly convex, minutely and confluently punctate posteriorly, grading to superficially roughened anteriorly; occipital carina indistinct; undersurface of head minutely punctate to superficially roughened; postgenal suture a well-developed longitudinal line that is darker than surrounding cuticle.

Promesonotal profile evenly convex to somewhat flat-topped, posterior portion more or less in same plane as sloping, flat dorsal face of propodeum; metanotal groove a small impression, anterior border of dorsal face of propodeum delimited with small, raised rim; dorsal and posterior faces of propodeum distinct, meeting at obtuse angle, dorsal face shorter than posterior face; propodeal spine laminar, translucent, triangular, acute, ventral margin curving into narrow infradental lamella that extends down posterior face to propodeal lobe; propodeal spiracle relatively large, directed posteriorly; dorsal promesonotum shallowly punctatorugulose; anterior and lateral pronotum, mesopleuron, lateral propodeum, dorsal and posterior faces of propodeum punctate; puncta smaller and shallower on mesopleuron and side of propodeum; without transverse carinulae between propodeal spines.

Petiolar peduncle joins anterior face of petiolar node at obtuse angle; petiolar node subquadrate, anterior face meeting dorsal face at right angle; transverse carina separates dorsal face and short, concave posterior face; ventral margin of petiole with strongly developed anteroventral tooth; postpetiole low and broad, with a shallow longitudinal sulcus dorsally and a distinct posteromedian impression; first gastral sternite lacking anterior sagittal keel; petiole, postpetiole, first gastral tergite covered with dense, small, puncta, interspaces less than or equal to width of puncta; first gastral sternite similar, but puncta and interspaces larger.

Dorsal surface of scape uniformly covered with short, decumbent, spatulate setae; leading edge of scape with projecting setae, shortest near apex, gradually lengthening to longest on basal lobe; ground pilosity of short, flattened, appressed to decumbent setae uniformly distributed across face, frontal lobes, clypeus, and undersurface of head; projecting specialized setae strongly spatulate to pompon-like, about 2x longer than wide, much larger than ground pilosity and highly differentiated from it, full complement 18, with curved anterior row of 8, transverse median row of 4, and posterior row of 6 on vertex margin; ground pilosity similar to that on face abundant on promesonotal dorsum, dorsal half of propodeal spines, dense on dorsa of petiolar node and postpetiole, sparser on first gastral tergite; 3 pairs projecting spatulate setae on promesonotum; legs with dense, strongly flattened, appressed to decumbent setae on apices of femora, posterior face of foretibia, entire midtibia, anterior face of hindtibia, somewhat sparser on other surfaces; apices of fore, mid and hind tibia with 2 larger spatulate seta; basitarsus and remaining tarsomeres with abundant, spatulate setae; two large spatulate setae on hind margin of dorsal face of petiolar node; row of 4 spatulate setae on hind margin of postpetiole, median pair smaller than lateral pair; specialized setae of first gastral tergite spatulate, full complement 4 pairs in two longitudinal rows, posterior pair flanked by additional pair (4 setae along posterior margin).

Color orange.

Queen
HW 0.67–0.68, HL 0.65–0.66, SL 0.40–0.41, SLL 0.09–0.11, CI 102–103, SLI 23–28 (n=2). Similar to worker in most respects; ocelli present; compound eye much larger than worker eye; anepisternum separated from katepisternum by U-shaped groove; metapleuron separated from propodeum by broad U-shaped groove; pronotum punctate; anepisternum punctate with smooth matte area anteroventrally; katepisternum punctate posteriorly, smooth and matte anteriorly; side of propodeum weakly punctate; bulla of metapleural gland smooth and matte; mesoscutum and scutellum punctate; axilla separated from scutellum by broad transverse trough with coarse longitudinal rugae; pronotum with 1 pair spatulate setae; mesoscutum with 6 setae, 2 lateral spatulate, medial 4 smaller, more clavate; axilla with spatulate seta; scutellum with 1 pair spatulate setae; first gastral tergite with number and arrangement of erect setae similar to worker.

Type Material
Holotype worker: Costa Rica, Heredia: 10km NE Vara Blanca, 10.23617 -84.11767, ±1 km, 1500 m, 13 Mar 2005, montane wet forest, ex sifted leaf litter (ALAS 15/WF/03/01), unique specimen identifier INB0003665110. Paratype workers: same data as holotype but 19 Mar 2005 (ALAS 15/WF/01/31), INB0003665287; same data but (ALAS 15/WF/01/35) , INB0003665317]; same data but (ALAS 15/WF/ 01/37) , INB0003665331; same data but (ALAS 15/WF/01/46) , INB0003665382; same data but (ALAS 15/WF/01/47) , INB0003665389]; same data but (ALAS 15/WF/01/39) , INB0003665349]; same data but 12 Apr 2005 (ALAS 15/WF/04/15) , INB0003668071; same data but (ALAS 15/WF/04/02) UVGC, INB0003667971.

Etymology
Xibalba was the Mayan underworld or "place of fear." It is a noun in apposition and thus invariant.

References based on Global Ant Biodiversity Informatics

 * Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
 * Longino J. T. 2013. A review of the Central American and Caribbean species of the ant genus Eurhopalothrix Brown and Kempf, 1961 (Hymenoptera, Formicidae), with a key to New World species. Zootaxa 3693(2): 101-151.
 * 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/