Megalomyrmex osadrifti

Known from types collected from rainforest leaf litter.

Identification
Boudinot et al. (2013) - Worker uniquely identified among Central American Megalomyrmex as follows: (1) katepisternum smooth and shining; (2) mandibular teeth, excluding apical two, small and fine; (3) occipital carina not visible in full-face view; (4) eyes of normal development and relatively close to anterolateral corner of clypeus (EL > 0.12 mm, OMI < 60); (5) scapes relatively long (SI > 90); (6) dorsal and posterior faces of propodeum meeting at broad curve. Queen similarly identifiable as worker, but with less robust petiolar and postpetiolar nodes, alate.

Sympatric with Megalomyrmex drifti, it is separated from this species by having a distinct basal and masticatory mandibular margins and M. osadrifti also has a well-rounded propodeum and relatively long scapes, whereas M. drifti has a dorsolaterally marginate and more angular propodeum. Furthermore, M. osadrifti is often larger (ML usually > 0.70 mm, vs. ML usually < 0.70 mm). Separated from Megalomyrmex megadrifti by the propodeum shape and the relatively short malar space (OMI < 60).

Distribution
Osa Peninsula (Puntarenas province) of Costa Rica; sea-level to 300 m elevation. Occurs in sympatry with M. drifti.

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

Nomenclature

 * . Megalomyrmex osadrifti Boudinot, et al. 2013: 57, figs. 41, 155-158, 241 (w.q.) COSTA RICA.
 * Type-material: holotype worker, 3 paratype workers, 1 paratype queen.
 * Type-locality: holotype Costa Rica: Puntarenas, 13 km. SSW Pto Jimenez, 8.40667°N, 83.3283°W±200 m., 130 m., 10.iii.2008, #JTL 6209-49, tropical rainforest, sifted litter (J.T. Longino); paratypes: 3 workers with same data, 1 queen with same data but #JTL 6209-26.
 * Type-depositories: MCZC (holotype); BMNH, MCZC, MZSP, USNM (paratypes).
 * Distribution: Costa Rica.

Worker
(holotype): HW 0.50, HL 0.58, SL 0.53, OMD 0.08, EL 0.16, ML 0.77, CI 85, SI 91, EI 33, OMI 49. (n=5): HW 0.48–0.52, HL 0.56–0.61, SL 0.50–0.57, OMD 0.06–0.09, EL 0.15–0.16, ML 0.73–0.80, CI 83–86, SI 87–93, EI 31–33, OMI 40–57.

Head Palpal formula 3,2. Basal and masticatory margins of mandible distinct, demarcated by an angle with a small tooth. Mandible with 5–6 teeth; apical two teeth largest, apical tooth slightly longer than subapical; 3–4 basal teeth small, evenly spaced or sometimes crowded somewhat anteriorly, away from basal tooth. Dorsal surface of mandible smooth and shining, interrupted by weak piligerous punctae. Clypeus truncate in profile view, with median seta often raised on a small tubercle. Clypeal carinae present, weak, and parallel until near anterior edge of clypeus. Clypeus, between antennal insertions, narrower than maximum width of scape. Antennal fossa surrounded by 2–3 complete carinulae. Malar area roughened in anterior half, smooth posteriorly. Compound eye with several ocular setae. Compound eye relatively close to lateral clypeal margin (OMI < 40). Scapes relatively long (SI > 90). Occipital carina short, distinct; obscured by vertex in full-face view; extending anteroventrally less than one eighth length of postgenal bridge. Mesosoma Katepisternum, promesonotum, and propodeum smooth and shining, excluding 3–4 close-set metapleural carinulae. Metapleural carinulae not reaching meso-metapleural suture. Metanotum deeply incised. Foraminal carina incomplete dorsomedially. Meso- and metabasitarsi tubular. Metasoma Petiole and postpetiole predominantly smooth and shining, except for girdling carinulae around posterior bases. Subpetiolar process a broad, truncate denticle in profile view. Postpetiolar sternum weakly dentate anteriorly. Lancets of sting apparatus flattened, narrow, broadening apically. Setation Fine; head dorsum with somewhat dilute longer suberect to erect setae in addition to short appressed to decumbent setae; scape with appressed to suberect setae; promesonotum with about 12 setae on each lateral half, about half of these setae long; first gastric tergum with somewhat dilute long subdecumbent to suberect setae in addition to numerous short appressed setae. Head, meso- and metasoma black to dark red-brown; mandibles, antennae, and legs yellow-brown.

Queen
(n=2): HW 0.58–0.59, HL 0.65, SL 0.57–0.60, OMD 0.08, EL 0.20–0.21, ML 0.95–0.99, CI 0.90, SI 0.89–0.91, OMI 0.38–0.39.

Similar to worker; differing by presence of an alate-condition mesosoma, stronger sculpturation and more pronounced propodeal angle.

Type Material
Holotype worker COSTA RICA, Puntarenas: 13 km SSW Pto. Jimenez, 8.40667°N 83.3283°W ±200 m, 130 m, 10 Mar 2008, tropical rainforest, ex sifted leaf litter (J.T. Longino#JTL6209-49) [CASENT0630909, ]. Paratype workers: (3) same data as holotype [CASENT0630907, ; CASENT0630908, ; CASENT0630910, ]. Paratype queen: (1) same data as holotype except #JTL6209-26 [CASENT0630911, MCZ].

Etymology
This species is morphologically similar to Megalomyrmex drifti and the Osa Peninsula of Costa Rica is the type locality.

References based on Global Ant Biodiversity Informatics

 * Boudinot B. E., T. P. Sumnicht, and R. M. M. Adams. 2013. Central American ants of the genus Megalomyrmex Forel (Hymenoptera: Formicidae): six new species and keys to workers and males. Zootaxa 3732(1): 1-82.
 * 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.