Strumigenys acarai Sosa-Calvo, Schultz

Jeffrey Sosa-Calvo, Ted R. Schultz & John S. Lapolla, 2010, A Review of the Dacetine Ants of Guyana (Formicidae: Myrmicinae), Journal of Hymenoptera Research 19, No. 1, pp. 11-43 : 26-30

Strumigenys acarai Sosa-Calvo, Schultz , and LaPolla, n. sp.

( Figs 26–39 )

Material examined. — Holotype: worker, labeled ‘‘ GUYANA: Upper Takutu-Upper Essequibo, Acarai Mountains, New Romeo Camp , 1069 m., 58 ° 57.828 ' W, 1 ° 19.938 ' N; 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 . (UGBC). Paratypes: 9 workers, labeled ‘‘ GUYANA: Upper Takutu-Upper Essequibo, Acarai Mountains, New Romeo Camp , 1069 m., 58 ° 57.828 ' W, 1 ° 19.938 ' N; 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. (BMNH (1), MCZC (1), and USNM (6))

Diagnosis (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.

Description (worker). —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 ( Fig. 30 ); 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 ( Fig. 35 ); 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.

Measurements: 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)

Gyne and male.— Unknown.

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.

Comments.— Strumigenys acarai seems to belong to the S. 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 S. carinithorax Borgmeier , 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 S. waiwai (described here) 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. The two species described here ( 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 ).

Figs 26–36 . Continued.

MODIFIED VERSION OF KEY IN BOLTON (2000)

In Bolton’s (2000) key, Strumigenys acarai will not key out to any of the known species. The key for the species of Strumigenys of the Neotropics can be modified as below to include S. acarai . Numbering of couplets follows Bolton (2000).

48. Cephalic dorsum with two pairs of short erect hairs that differ from other cephalic ground-pilosity, one pair close to occipital margin, other close to highest point of vertex. Ventral surface of petiole with curtain or fringe of spongiform tissue, or at least with spongiform lobes linked by carina......... couplet 49 of Bolton (2000)

– Cephalic dorsum without or with one pair of short erect hairs that differs from other cephalic ground-pilosity, when one present it is close to occipital margin. Ventral surface of petiole without spongiform tissue, sometimes with rounded or angular anteroventral cuticular process....... 52a (different to couplet 52 in Bolton 2000)

52a. Mandible with minute inconspicuous denticle close to midlength.... acarai new species

– Mandible with 1 or 2 very conspicuous spiniform preapical teeth, distal one in apical third, proximal one close to midlength.............. couplet 52 in Bolton (2000)

Figures

Figs 26–36. Scanning electron micrographs of a paratype worker of Strumigenys acarai, new species. 26, Head and mandibles in full-face view. 27, Cephalic capsule in full-face view. 28, Mandibles in dorsal view. 29, Tooth on inner margin of mandibles in dorsal view. 30, antennal scapes and hairs on leading edge of scape in full-face view. 31, Lateral view. 32, Dorsal view. 33, Lateral view of mesosoma. 34, Dorsal view of mesosoma. 35, Dorsal view of waist segments (petiole and postpetiole). 36, Dorsal view of postpetiole and first gastral tergite.

Figs 37–39. Automontage images of the holotype worker of Strumigenys acarai, new species. 37, Full-face view. 38, Lateral view. 39, Dorsal view.