Strumigenys acarai

The types were collected from leaf litter.

Identification
Sosa-Calvo et al. (2010) - worker: Small (TL 1.62–1.79); eyes vestigial, consisting of one or two ommatidia; masticatory margin of mandibles with an inconspicuous tooth, visible under high magnifications; leading edge of antennal scapes with some hairs that curve toward the base of scape; dorsum of promesonotum rugulose and with a conspicuous median longitudinal ruga that extends for entire length of promesonotum; petiole lacking a ventral process or spongiform tissue of any kind.

Strumigenys acarai  seems to belong to the Strumigenys silvestrii species group (sensu Bolton 2000), sharing with some members of that group: (i) the ventral margin of petiole lacking spongiform tissue; (ii) the small worker size (HL 0.39–0.43, HW 0.29–0.33, TL 1.62–1.79, WL 0.38–0.42 in S. acarai, HL 0.36–0.52, HW 0.28–0.44, TL 1.5–2.2, WL 0.36–0.56 in the S. silvestrii group); (iii) the apical fork of mandibles lacking intercalary denticles; (iv) the leading edge of the antennal scapes having two or more hairs that are curved or inclined toward the base of the scape; (v) the eyes minute, usually with only 1–3 ommatidia in total; (vi) the preocular carina short and ending before the level of the eye; (vii) the propodeal spines usually present; and (viii) the head and alitrunk usually sculptured but the mesopleuron and metapleuron entirely smooth and shining.

Strumigenys acarai shares with Strumigenys carinithorax, in addition to the character states mentioned above, the presence of a median fine longitudinal carina on the mesonotum. Strumigenys acarai differs from S. carinithorax, however, by having the ground-pilosity of the head, from above level of eye to close to occipital margin, very narrowly spatulate (almost simple) rather than spatulate as in S. carinithorax; the mandibles with a pair of minute inconspicuous preapical denticles proximal to the midlength of the mandibles rather than with a pair of spiniform preapical teeth as found in S. carinithorax, which are located in the distal third, and with a minute pair of denticles that may be difficult to see that are just proximal to the midlength of the mandibles (Bolton 2000); the leading edge of the antennal scapes with some multifurcated narrowly spatulate hairs rather than spoon-shaped hairs of S. carinithorax. Strumigenys acarai shares with Strumigenys waiwai the presence of multifurcated hairs. In the former species, however, these hairs seem to be restricted to the leading edge of the antennal scapes, whereas in the latter these hairs are present on the dorsum of the head. S. acarai and S. waiwai also differ from each other in mandibular dentition (inconspicuous pair of teeth at midlength of mandibles in S. acarai, and having a pair of spiniform teeth and a minute, but conspicuous pair of teeth at midlength of mandibles in S. waiwai), in the sculpture of the dorsum of the promesonotum (rugulose and with a conspicuous median longitudinal ruga in S. acarai, and strongly aerolate in S. waiwai), and in the length of the costulae on first gastral tergite (longer than the maximum length of the disc of postpetiole in S. acarai, and barely as long as the disc of postpetiole in S. waiwai).

Distribution based on Regional Taxon Lists
Neotropical Region: Guyana.

Castes
Known only from the worker caste.

Nomenclature

 *  acarai. Pyramica acarai Sosa-Calso, Schultz & LaPolla, 2010: 26, figs. 26-39 (w.) GUYANA.

Worker
holotype (and paratypes): GL = 0.40 (0.35–0.41), HL = 0.42 (0.39–0.41), HW = 0.31 (0.29–0.33), ML = 0.25 (0.24–0.25), PL = 0.20 (0.15–0.19), PPL = 0.09 (0.08–0.11), PW = 0.18 (0.17–0.19), SL = 0.29 (0.27–0.30), TL = 1.77 (1.62–1.79), WL = 0.41 (0.38–0.42).

Indexes: CI = 73 (74–81), MI = 59 (58–64), PI = 48 (38–51), SI = 94 (88–96). (n = 10)

Head: mandibles elongate with outer margin convex; inner margin of mandibles with minute inconspicuous preapical denticle in mandible’s midlength, visible under high magnification; apical fork of mandibles lacking intercalary teeth; anterior margin of clypeus slightly concave or transverse; dorsum of antennal scape imbricate; anterior edge of antennal scape with at least 3 narrowly spatulate hairs curving toward base, some hairs on scape multi-furcate; hairs on upper margin of scrobe narrowly spatulate and curving anteriorly; apicoscrobal hair flagellate; dorsum of head strongly areolate; ocular carina failing to reach level of eyes; eyes minute, with only 1 (one paratype, most of them with two) or 2 ommatidia; dorsum of head with fine subdecumbent hairs, some of which curve medially and with pair of erect hairs present on cephalic margin (very difficult to see).

Mesosoma: humeral hair flagellate; anterior portion of pronotum, in dorsal view, strongly reticulate; dorsum of promesonotum rugulose and with conspicuous median longitudinal ruga or carina that extends for entire length of promesonotum; areas between rugae smooth and shining; dorsum of promesonotum with subdecumbent hairs that curve medially, most hairs directed backwards; posterior half of promesonotum areolate; mesonotum with pair of flagellate simple hairs; dorsum of propodeum and declivity of propodeum areolate; mesopleuron and metapleuron mostly smooth and shining; mesopleuron and metapleuron divided by strip of aerolate sculpture that originates at ventral margin of mesopleuron and metapleuron and extends dorsally in direction of metanotal groove, this strip incomplete, fading before it connects with metanotal groove; propodeal spines long; declivity of propodeum with a thin carina.

Metasoma: dorsum and sides of petiole strongly areolate; ventral margin lacking spongiform tissue or process of any kind; node of petiole, in lateral view, with two transverse rows each consisting of four long subdecumbent and simple hairs and composed of two hairs medially and two hairs distally; posterior margin of petiolar node with small spongiform crest, best seen in fronto-dorsal view; in dorsal view, lateral projections of crest conspicuous and triangular; postpetiole with ventral and lateral spongiform lobes well developed; dorsum of postpetiole with longitudinal rugae, areas between rugae smooth and shining; base of first gastral sternite bearing conspicuous pad of spongiform tissue; basigastral costulae longitudinal and sharply defined, longer than maximum length of disc of postpetiole; dorsum of first gastral tergite with numerous long flagellate hairs; entire tergite posterior to basigastral costulae smooth and shining.

Type Material
Holotype: worker, labeled ‘‘GUYANA: Upper Takutu-Upper Essequibo, Acarai Mountains, New Romeo Camp, 1069 m., 58°57.8289W, 1°19.9389N; 14.x.2006; T. R. Schultz, J. Sosa-Calvo, C. J. Marshall, R. Williams; 1° upland forest; leaf-litter sample. (JSC061014-01)’’ USNM ENT No. 00537294. .

Paratypes: 9 workers, labeled ‘‘GUYANA: Upper Takutu-Upper Essequibo, Acarai Mountains, New Romeo Camp, 1069 m., 58°57.8289W, 1°19.9389N; 14.x.2006; T. R. Schultz, J. Sosa-Calvo, C.J. Marshall, R. Williams; 1° upland forest; leaf-litter sample. (JSC061014-02, JSC061014-03). USNM ENT No. 00537295–00537303. ( (1), (1), and  (6))

Etymology
The name of this species refers to the Acarai Mountains, in the Upper Takutu-Upper Essequibo region of southern Guyana, where specimens of this species were collected.

References based on Global Ant Biodiversity Informatics

 * Sosa-Calvo J., T. R. Schultz, and J. S. LaPolla. 2010. A review of the dacetine ants of Guyana (Formicidae: Myrmicinae). Journal of Hymenoptera Research 19: 12-43.