Monomorium infuscum Heterick

Fig. 28.

Etymology.- Latin "infuscus" ("dusky" "dark brown" "blackish")

Material examined.- Holotype: [[worker]], Prov. Toamasina, 5.3 km SSE Ambanizana, Andranobe, 15°40'S, 49°58'E 425 m 21.xi.1993 B.L. Fisher #926(43)-12/sifted litter (leaf mold, rotten wood) rainforest (CAS). Paratypes: Prov. Toamasina (all specimens with same collection data as holotype): 1 [[worker]] (ANIC); 12 [[worker]] (BMNH); 12 [[worker]] (MCZ).

Other material examined: Prov. Toamasina: 6.9 km NE Ambanizana, Andranobe, 2.xii.1993 (3 [[worker]]) 8.xii.1993 (3 [[worker]]) 9.xii.1993 (3 [[worker]]) B.L. Fisher; Ambanisana, P.N. Masoala 2-6.iii.2003 Silva et al. (1 [[worker]]).

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 around 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 always well-defined; anteromedian clypeal margin emarginate, clypeal carinae terminating in blunt angles, or, emarginate, clypeal carinae terminating in small denticles; paraclypeal setae moderately long and fine, curved; 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).

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, dorsum and sides of propodeum mainly smooth, with weak to strong striolae on declivitous face and on metapleuron; propodeal dorsum flat throughout most of its length; propodeum smoothly rounded or with indistinct angle; 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 sharp, acute angled flanges.

Petiole and postpetiole: Petiolar spiracle lateral 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) between 1:1 and 3:4; anteroventral petiolar process present as a thin flange tapering posteriad; ventral petiolar lobe absent; height ratio of petiole to postpetiole about 4:3; height-length ratio of postpetiole between 1:1 and 3:4; 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 dark reddish- or yellowish-brown. Worker caste monomorphic.

Holotype measurements: HML 3.22 HL 1.04 HW 0.98 CeI 94 SL 0.94 SI 96 PW 0.72.

Other worker measurements: HML 2.87-3.63 HL 0.96-1.16 HW 0.86-1.07 CeI 89-96 SL 0.86-1 00 SI 92-99 PW 0.63-0.78 (n=15).

Remarks.- Monomorium infiiscum is known only from a few workers from three sites near Ambanizana, Toamasina Province. Samples have been collected from rotten wood, sifted leaf litter and pitfall trap, in rainforest. Differences between this species and the very similar M. aureorugosum are provided in "Remarks" under the latter species.