Eurhopalothrix oscillum

This species inhabits mature wet forest from mid-elevation slopes to lower cloud forest. It is known from 300–1500 m elevation, but is most abundant from 500–1000 m. All specimens are from Winkler samples of sifted litter and rotten wood from the forest floor. On Cerro Saslaya in Nicaragua, sampling along an elevational transect from 300–1600 m yielded the species in samples from 760–1180 m. It occurred in 11% of miniWinkler samples at a 1000 m site that was intensively sampled but did not occur at a similarly sampled 300 m site. Similarly, on Cerro Musún, a transect from 700–1400 m yielded the species in the 1000–1100 m interval. In the Peñas Blancas Valley in the Cordillera de Tilarán, Costa Rica, it is moderately frequent in Winkler samples at 800 m elevation, but does not occur above 1000 m. On the Barva Transect in the Cordillera Volcánica Central, it occurred in 1% of miniWinkler samples at 300 m elevation and 5% of miniWinkler samples at 500 m elevation. It was not encountered at similarly sampled sites at 1100 m, 1500 m, and 2000 m. (Longino 2013)

Identification
Mandible with single tooth row; face with 18 specialized spatulate setae; ground pilosity of face spatulate, decumbent, weakly differentiated from specialized projecting setae, extending across entire face, including median area and frontal lobes; pronotum with 1 pair spatulate setae, lacking on mesonotum; first gastral tergite with at most 3 pairs spatulate setae in two longitudinal rows. Similar to Eurhopalothrix circumcapillum, Eurhopalothrix megalops, Eurhopalothrix ortizae, Eurhopalothrix schmidti, Eurhopalothrix semicapillum. (Longino 2013)

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

Nomenclature

 *  oscillum. Eurhopalothrix oscillum Longino, 2013: 133, figs. 14C, 27, 36 (w.) COSTA RICA.

Worker
HW 0.67–0.70, HL 0.64–0.67, SL 0.37–0.40, SLL 0.03–0.05, CI 100–108, SLI 9–13 (n=7). Labrum anterolateral gibbosities of basal portion developed as sharply right-angled, ventrally-directed teeth, apical portion elongate, flexed dorsally, relatively narrow, with a minute notch at apex; apex with a fringe of short, non-capitate translucent setae; mandible triangular, dorsal surface convex, smooth and shining apically, grading to punctate basally, rounding into ventral surface; interior surface concave, smooth and shining; masticatory margin a single row of 11 flattened acute triangular teeth, basal tooth broader and less acute than other teeth, more laminar and translucent; scape with moderately developed basal lobe; scrobe deep, sharply delimited dorsally and ventrally, abutting deep antennal socket; surface of scrobe very faintly punctate, sublucid; eye small, about 5 ommatidia across greatest diameter; clypeus approximately planar, uniformly punctate, dull; sides of head above eyes moderately angulate; surface of face uniformly convex and uniformly sculptured with dense, confluent puncta; occipital carina indistinct; undersurface of head uniformly punctate; postgenal suture a well-developed longitudinal trough, darker than surrounding cuticle.

Promesonotal profile forming an even convexity, meeting flat dorsal face of propodeum at obtuse angle; 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 rounding into narrow infradental lamella that extends down posterior face to propodeal lobe; propodeal spiracle small, directed posteriorly in small concavity between base of propodeal spine and dorsum of metapleural gland bulla; all of mesosoma except posterior face of propodeum uniformly punctate with smooth interspaces; posterior face of propodeum smooth to very faintly sculptured; no transverse carinae between bases of propodeal spines; puncta on promesonotum larger than those on katepisternum and side of propodeum; interspaces sublucid on promesonotum, more matte on katepisternum and side of propodeum.

Petiolar peduncle joins anterior face of petiolar node at rounded obtuse angle; anterior face of node meets sloping flat dorsal face at rounded right angle; posterior face of node very short; ventral margin of petiole with short, acute, anteroventral tooth; postpetiole low and broad, with a broad longitudinal sulcus dorsally; first gastral sternite lacking anterior sagittal keel; petiole, postpetiole, and gaster densely sculptured with confluent puncta.

Dorsal surface of scape covered with uniform short, decumbent, spatulate setae; leading edge of scape with projecting spatulate setae, short near apex of scape, gradually lengthening to longest setae on basal lobe; ground pilosity on clypeus sparse, narrow, fully appressed; ground pilosity of face larger, similar in shape and slightly larger than those on scape, decumbent, more or less uniformly distributed across entire face, including frontal lobes; projecting specialized setae spatulate, about twice as long as wide, curved, about twice as large as ground pilosity (and thus not highly differentiated from it), full complement typically 18, with curved anterior row of 8, transverse median row of 4, and posterior row of 6 on vertex margin; ground pilosity present on promesonotal dorsum and dorsal margin of propodeal spine, similar in size and shape to that on scape but sparser; typically one pair of projecting spatulate setae on pronotum, similar to those on face; legs with ground pilosity similar to that on face, dense on apices of femora, dorsal and anterior faces of mid and hind tibia, dorsal and posterior face of foretibia, sparser elsewhere; apex of foretibia with 1 larger spatulate seta, apices of mid and hind tibia with 2; basitarsus with 3–5 pairs suberect clavate setae, remaining tarsomeres each with pair of suberect clavate setae, tarsal setae smaller on foretarsus than on mid and hind tarsus; 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; first gastral tergite with very sparse, very thin, fully appressed ground pilosity, but relatively conspicuous because lighter colored than dark cuticle; larger specialized setae clavate, full complement 3 pairs in two longitudinal rows, but full complement rarely all present.

Color dark brown.

Queen
HW 0.68–0.70, HL 0.66–0.70, SL 0.38–0.39, SLL 0.04–0.05, CI 100–102, SLI 9–14 (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; puncta fading on anterodorsal katepisternum, leaving small smooth patch; pronotum with 1 pair spatulate setae; mesoscutum with 6 straight, erect, narrowly clavate setae; axilla with clavate seta; scutellum with 1 pair spatulate setae; first gastral tergite with number and arrangement of erect setae similar to worker, but setae straight, longer, more narrowly clavate.



Type Material
Holotype worker: Costa Rica, Alajuela: Casa Eladio, Rio Peñas Blancas, 10.30877 -84.7165, ± 1km, 830 m, 10 May 1989, wet forest, ex sifted leaf litter (J. Longino#2529-s), unique specimen identifier INBIOCRI001281403. Paratype workers: same data as holotype, CASENT0639387, CASENT0639388; , CASENT0639389; , CASENT0639390; , CASENT0639391; , CASENT0639392; , CASENT0639393; , CASENT0639394; , CASENT0639395; , CASENT0639396, CASENT0639397.

Etymology
Latin for mask, in reference to the mask-like faces of Eurhopalothrix. It is a noun in apposition and thus invariant.

References based on Global Ant Biodiversity Informatics

 * 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/