Monomorium aureorugosum Heterick

Figs. 28, 73-74.

Etymology.- Latin "aureus" ("golden") + "rugosus" ("wrinkled")

Material examined.- Holotype: [[worker]], Prov. Toamasina, 6.9 km NE Ambanizana, 15°34'S, 50°00'E 825m 2.xii.1993 B.L. Fisher #976(41)-19/sifted litter (leaf mold, rotten wood) rainforest (CAS). Paratypes: Prov. Toamasina (specimens with same collection data as holotype): 1 [[worker]] (ANIC) 12 [[worker]] (BMNH); 1 [[worker]] (CAS) 23 [[worker]] (MCZ).

Other material examined: Prov. Antsiranana: RNI Marojejy, 20.xi.1993 Alpert et al. (4 [[worker]]) (MCZ); RNI Marojejy, 10 km NW Manantenina 15-22.x.1996 (1 [[worker]]). Prov. Toamasina: P.N. Masoala, 26.ii-2.iii.2003 D. Silva et al. (1 [[worker]]); 1 km W Sahafary, along Onive River, Masoala Peninsula 25.iv.1996 Alpert et al. (16 [[worker]]) (MCZ).

Worker description.- Head: Head oval; vertex planar or weakly concave; frons shining and smooth except for piliferous pits; pilosity of frons a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter decumbent setae or setulae. Eye moderate, eye width 1-1.5x greatest width of antennal scape; (in full-face view) eyes set above midpoint of head capsule; (viewed in profile) eyes set anteriad of midline of head capsule; eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin. Antennal segments 12; antennal club not clearly defined. Clypeal carinae indicated by multiple weak ridges; anteromedian clypeal margin broadly convex; paraclypeal setae short and thickened, not reaching basal margin of closed mandibles; posteromedian clypeal margin approximately level with antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes sinuate, divergent posteriad. Psammophore absent. Palp formula 2,2. Mandibular teeth five; mandibles triangular and smooth (except for piliferous pits); masticatory margin of mandibles approximately vertical or weakly oblique; basal tooth approximately same size as t4 (five teeth present), or, smaller than t4 (five teeth present).

Mesosoma: Promesonotum shining, with whorls of rugae on sides of promesonotum, these becoming longitudinal on dorsum; (viewed in profile) promesonotum broadly convex; promesonotal setae greater than twelve; standing promesonotal setae a mixture of well-spaced, distinctly longer, erect and semi-erect setae which are curved distally and often paired, interspersed with much shorter, incurved, decumbent setae; appressed promesonotal setulae few, mainly on sides of promesonotum. Metanotal groove absent. Propodeum shining, with strong, transverse rugae dorsally, laterally and on declivitous face; propodeal dorsum flat throughout most of its length; propodeum always smoothly rounded; standing propodeal setae consisting of two or more prominent pairs anteriad, often with another pair of prominent setae posteriad, and other smaller setae on/around dorsal and declivitous surfaces of propodeum; appressed propodeal setulae very sparse or absent; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum. Vestibule of propodeal spiracle absent or not visible. Propodeal lobes present as blunt-angled flanges; Petiolar spiracle laterodorsal and situated slightly anteriad of petiolar node; node (viewed in profile) broad and thick, with short vertex anteriad, node sloping posteriad; appearance of node transversely rugose, shining between sculpture; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 1:1.

Petiole and postpetiole: Anteroventral petiolar process present as a thin flange tapering posteriad to absent or vestigial; ventral petiolar lobe absent; height ratio of petiole to postpetiole between 4:3 and 1:1; height-length ratio of postpetiole about 1:1; postpetiole strongly rugose; postpetiolar sternite not depressed at midpoint, its anterior end an inconspicuous lip or small carina.

Gaster: Pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with a few appressed setulae.

General characters: Color head, gaster and appendages yellow, mesosoma reddish-orange. Worker caste monomorphic.

Holotype measurements: HML 3.61 HL 1.12 HW 1.02 CeI 91 SL 1.02 SI 100 PW 0.75.

Other worker measurements: HML 3.52-3.90 HL 1.10-1.20 HW 1.00-1.09 CeI 89-93 SL 1.02-1.07 SI 98-103 PW 0.74-0.82 (n=13).

Remarks.- Monomorium aureorugosum is one of two very large members of the M. hildebrandti group with a restricted range in far north-eastern Madagascar. This ant, along with M. infuscum , is known only from a small number of workers. Because their ranges overlap, and they are clearly closely related, it is tempting to combine the two forms. However, they appear to represent distinct species, not only because there exist no examples of intermediate color, but because there are subtle but consistent differences in the morphometrics pertaining to the antennal scape (i.e., the SL for M. aureorugosum is 1.02-1.10mm, while that for M. infiiscum is 0.86-1.00mm, and their respective SI"s are 98-103 and 92-99).

Monomorium aureorugosum is known from Antsiranana and Toamasina provinces, where it appears to be confined to rainforest. A nest series has been collected from soil below tree roots by researchers from MCZ. Individual workers have been taken from sifted leaf litter, and in pitfall, Winkler and yellow pan traps.