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Monomorium exiguum Forel HNS

Figs. 18, 51-52.

Monomorium exiguum Forel HNS 1894a:85. Syntype [[worker]]"s (lectotype here designated), Ethiopia: (locality on label now illegible, but given as "Suedabessinien" in Bolton 1987) (MHNG) [examined].

Monomorium (Martia) exiguum Forel HNS 1913b:351.

Monomorium (Lampromyrmex) exiguum Forel HNS : Wheeler W.M. 1922:876.

Monomorium (Mitara) exiguum var. bulawayensis HNS [sic] Forel 1913c:217. Syntype [[worker]]"s (lectotype here designated), Zimbabwe: Bulawayo (MHNG) [examined].

Monomorium (Lampromyrmex) exiguum bulawayensis Forel HNS : Wheeler, W.M. 1922:876. Syn. under Monomorium exiguum Forel HNS : Bolton 1987:388.

Monomorium (Mitara) faurei Santschi HNS 1915: 260, fig. 10 ([[worker]]). Syntype [[worker]]"s (lectotype here designated), Gabon (MHNG) [examined].

Monomorium (Lampromyrmex) faurei Santschi HNS : Wheeler, W.M. 1922:876. Syn. under Monomorium exiguum Forel HNS : Bolton 1987:388.

Monomorium (Mitara) exiguum r. flavescens Forel HNS 1916:418. Syntype [[worker]]"s, Democratic Republic of Congo: St. Gabriel, Stanleyville (MHNG) [examined].

Monomorium (Lampromyrmex) exiguum flavescens Forel HNS : Wheeler, W.M. 1922:876. Syn. under Monomorium exiguum Forel HNS : Bolton 1987:388.

Monomorium minutissimum Santschi HNS 1937:225, figs. 27, 28. Syntype [[worker]] (lectotype here designated), Angola, Ebanga Rd. (NHMB) [examined]. syn. n. Syn. under Monomorium mictile Forel HNS : Bolton 1987:388.

Material examined.- M. exiguum HNS : Lectotype: [[worker]], Ethiopia, Ilg (MHNG). In view of the variability, particularly in color, that led researchers to erect new "varieties" for this species, a lectotype has been chosen for M. exiguum HNS that fixes the species name for populations with dark, longer-headed specimens that have the characteristics mentioned in the original description. This particular specimen has been glued in the normal way, dorsal surface uppermost. Paralectotype: [[worker]], same data as lectotype, here designated for a specimen that has been pointed on the same pin as the lectotype and glued on its back. This specimen has been repinned with photocopies of the original labels (MHNG). M. exiguum bulawayense HNS (corrected ending): Lectotype: [[worker]], Zimbabwe, Arnold (MHNG). The lectotype fixes this name for populations with dark, shorter headed specimens as mentioned in the description for M. exiguum bulawayense HNS . The carded lectotype specimen is the one glued on the RHS of the card (the head of the LHS specimen is damaged). Paralectotype: [[worker]], same data as lectotype (MHNG). (No effort has been made to separate the fragile, carded lectotype and paralectotype.). M. faurei HNS : Lectotype: [[worker]], Gabon, F Faure, 1914 (NHMB Reg. No. 203). The lectotype fixes the name for populations of M. exiguum HNS with a slightly bicolored appearance (i.e., yellowish-brown head and gastral apex and yellowish mesosoma, nodes, appendages and gastral base. The sides of the gaster in this form are often infuscated). The carded lectotype is the single specimen on the top card rectangle on a pin holding three rectangles. Paralectotypes: (i) Four carded workers, same data as the lectotype (bottom two rectangles) (NHMB). (ii) One worker and two detached worker heads mounted between two cover clips, these held by a pinned slip of cardboard, "Guinea fr." [Guinea], Mamou, Silvestri (NHMB). M. exiguum flavescens HNS : Lectotype: [[worker]], Democratic Republic of Congo: St. Gabriel, Stanleyville, Kohl (MHNG). The lectotype fixes the name for populations with relatively pale workers with a strongly constricted mesosoma as mentioned in the description of M. exiguum flavescens HNS . Paralectotype: (i) One worker, same data as lectotype (MHNG). This paralectotype has been removed from the same pin as the lectotype and repinned with photocopies of the original labels. (ii) Two workers, same data as the lectotype (MNHG). M. minutissimum HNS : Lectotype: [[worker]], Angola, Ebanga Rd., A. Monard, 16.xi.1932 (NHMB - Reg. No. 207). The lectotype fixes the name for populations of this taxon, which appears to be essentially the same as M. faurei HNS , though said by Santschi to have a more deeply incised metanotal groove. The lectotype is headless. (NB. This specimen is described as a "holotype" by Bolton (1987), but Santschi clearly examined more than one specimen as is indicated by the range of body length given in his description. However, no other syntype specimens are known to still exist.).

Other material examined: Prov. Antananarivo: Res Ambohitantely, 24.1 km 59 NE Ankazobe 17-22.iv.2001 Rabeson et al. (1 [[worker]]); Ambohitantely, 20.9 km 72 NE Ankazobe 17-22.iv.2001 Rabeson et al. (4 [[worker]]). Prov. Antsiranana: Montagne Francais, 7.2 km 142 SE Diego Suarez 22-28.ii.2001 Fisher et al. (1 [[worker]]); Reserve Ambre, 3.5 km 235 SW Sakaramy 26-31.i.2001 Fisher et al. (1 [[worker]]); Res. Spec. Ankarana, 22.9 km 224 SW Anivorano Nord 10-16.ii.2001 Fisher et al. (1 [[worker]]) 6-20.iii.2001 R. Harin Hala (6[[male]]). Prov. Fianarantsoa: 28 km SSW Ambositra, Ankazomivady 9.i.1998 (4[[worker]], 1[[queen]]), 11.i.1998 (3[[queen]]), 14.i.1998 (1 [[worker]]) BL. Fisher. Prov. Mahajanga: P. N. Ankarafantsika, Ampijoroa, 40 km 306 NW Andranofasika 26-31.iii.2001 Fisher et al. (2 [[worker]]); P. N. Ankarafantsika, Ampijoroa, 5.4 km 331 NW Andranofasika 26-31.iii.2001 Rabeson et al. (26 [[worker]], 1 [[queen]]); P. N. Ankarafantsika, Ankoririka, 10.6 km 13 NE Tsaramandroso 9-14.iv.2001 Rabeson et al. (9 [[worker]]); P. N. Tsingy de Bemaraha, 3.4 km 93 E Bekopaka 6-10.xi.2001 Fisher et al. (5 [[male]]); P. N. Tsingy de Bemaraha, 10.6 km 123 ESE Antsalova 16-20.xi.2001 Fisher et al. (4 [[worker]]). Prov. Toamasina: SF Tampolo, 10 km NNE Fenoarivo Atn. 10.iv.1997 BL. Fisher (1 [[worker]]). Prov. Toliara: Beza-Mahafaly, 27 km E Betioky 23.iv.1997 BL. Fisher (49 [[worker]], 7 [[queen]]); Cap Sainte Marie, 12.3 km 262 W Marovato 11-15.ii.2002 Fisher et al. (6 [[queen]]); Cap Sainte Marie, 14.9 km 261 W Marovato 13-19.ii.2002 Fisher et al. (3 [[worker]]); Foret Mahavelo, Isantoria Riv., 5.5 km 37 NE Ifotaka 31.i.2002 Fisher et al. (59[[worker]], 7[[queen]]); Foret de Petriky, 12.5 km W 272 Tolagnaro 22.xi.1998 B.L. Fisher (3 [[worker]]); Mahafaly Plateau, 6.2 km 74 ENE Itampolo 25.ii.2002 Fisher at al. (7[[male]]); P. N. Kirindy Mite, 16.3 km 127 SE Belo sur Mer 6-10.xii.2001 Fisher et al. (3 [[queen]]); P. N. Andohahela, 1.7 km 61 ENE Tsimelahy 16-20.i.2002 Fisher et al. (40[[worker]], 7[[queen]]); 2.7 km WNW Ste Luce, 9-11.xii.1998 B.L. Fisher (1[[worker]]); Vohibasia Forest, 59 km NE Sakaraha 13 i. 1996 BL. Fisher (6 [[worker]]).

Worker description.- Head: Head rectangular, 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 below 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 11; antennal club three-segmented. Clypeal carinae weakly to strongly defined; anteromedian clypeal margin straight; 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 straight, parallel. Psammophore absent. Palp formula2,2. Mandibular teeth three, plus minute, basal denticle or angle; mandibles with sub-parallel inner and outer margins, smooth (except for piliferous pits); masticatory margin of mandibles approximately vertical or weakly oblique; basal tooth a small to minute denticle or angle, much smaller than t3 (four teeth present).

Mesosoma: Promesonotum shining and mainly smooth, vestigial striolae, if present, confined to lower anterior mesopleuron; (viewed in profile) anterior promesonotum smoothly rounded, thereafter more-or-less flattened; promesonotum on same plane as propodeum, promesonotal setae seven to 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 strongly impressed, with distinct transverse costulae, or, metanotal groove vestigial. Propodeum shining and smooth, with a few weak striolae on metapleuron; propodeal dorsum convex; propodeum always smoothly rounded; standing propodeal setae consisting of one prominent pair anteriad, with other shorter setae very sparse or absent; 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 vestigial flanges or small strips of cuticle only.

Petiole and postpetiole: Petiolar spiracle lateral and situated within anterior sector of petiolar node; node (viewed in profile) conical, vertex tapered; appearance of node shining and smooth throughout; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 1:1; anteroventral petiolar process absent or vestigial; ventral petiolar lobe present; height ratio of petiole to postpetiole between 3:2 and 4:3; height-length ratio of postpetiole about 1:1; postpetiole shining and smooth; postpetiolar sternite without anterior lip or carina, or this structure vestigial.

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

General characters: Color variable, pale yellow to brown. Worker caste monomorphic.

Lectotype worker measurements ( M. exiguum HNS ): HML 0.93 HL 0.36 HW 0.28 CeI 78 SL 0.22 SI 79 PW 0.18.

Lectotype worker measurements ( M. exiguum bulawayense HNS ): HML 1.00 HL 0.39 HW 0.32 CeI 81 SL 0.26 SI 83 PW 0.20.

Lectotype worker measurements ( M. faurei HNS ): HML 0.88 HL 0.35 HW 0.29 CeI 83 SL 0.22 SI 76 PW 0.18.

Lectotype worker measurements ( M. exiguum flavescens HNS ): HML 0.89 HL 0.36 HW 0.30 CeI 82 SL 0.22 SI 75 PW 0.18.

Lectotype worker measurements ( M. minutissimum HNS ): No measurements taken as lectotype is headless.

Other worker measurements (non-types): HML 0.79-0.97; HL 0.33-0.39 HW 0.26-0.29 CeI 73-81 SL 0.22-0.26 SI 81-93 PW 0.16-0.20 (n=20).

Queen description.- Head: Head rectangular; vertex weakly concave or planar; 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 setae or setulae, which are decumbent or appressed, longer setae thickest on vertex. Eye elliptical, margin sometimes shallowly concave; (in full-face view) eyes set at about midpoint of head capsule; (viewed in profile) eyes set posteriad of midline of head capsule.

Mesosoma: Anterior mesoscutum smoothly rounded, thereafter more-or-less flattened; pronotum, mesoscutum and mesopleuron shining and mainly smooth, vestigial striolae, if present, confined to anterior katepisternum; length-width ratio of mesoscutum and scutellum combined between 2:1 and 3:2; axillae contiguous, or nearly so; standing pronotal/mesoscutal setae a mixture of well-spaced, distinctly longer, erect and semi-erect setae which are curved distally, interspersed with much shorter, incurved, decumbent setae; appressed pronotal, mescoscutal and mesopleural setulae few, mainly on sides of pronotum and mesopleuron. Propodeum shining and smooth, with a few weak striolae on metapleuron; propodeum smoothly rounded or with indistinct angle; propodeal dorsum convex; standing propodeal setae consisting of up to a dozen or more longer erect and shorter sub-erect setae; appressed propodeal setulae very sparse or absent; propodeal spiracle nearer metanotal groove than declivitous face of propodeum; propodeal lobes present as vestigial flanges only, or absent.

Wing: Wing not seen (queens dealated).

Petiole and postpetiole: Petiolar spiracle lateral and situated slightly anteriad of petiolar node; node (viewed in profile) cuneate, vertex tapered; appearance of node shining, with vestigial sculpture; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 2:1 and 1:1; anteroventral petiolar process present as a thin flange tapering posteriad; height ratio of petiole to postpetiole between 4:3 and 1:1; height -length ratio of postpetiole between 4:3 and 1:1; postpetiole shining and weakly striolate posteriad; postpetiole shining and smooth; postpetiolar sternite without anterior lip or carina, or this structure vestigial (NB. May be confused with rear margin of postpetiolar sternite, which does project as a spur, length of sternite being much reduced).

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

General characters: Color yellowish-brown. Brachypterous alates not seen. Ergatoid or worker-female intercastes seen.

Queen measurements: HML 1.55-2.00 HL 0.45-0.55 HW 0.39-0.54 CeI 83-98 SL 0.34-0.42 SI 75-90 PW 0.28-0.55 (n=19).

Male description.- Head: (In full-face view) head width-mesosoma width ratio between 1:1 and 3:4; frons finely micropunctate. Compound eyes protuberant and elliptical tending to elongate; margin of compound eye clearly separated from posterior margin of clypeus. Ocelli turreted. Ratio of length of first funicular segment of antenna to second funicular segment between 1:1 and 3:4. Maximum number of mandibular teeth and denticles three.

Mesosoma: Mesoscutum broadly convex; pronotum and mesoscutum shining and mainly smooth, vestigial striolae, if present, confined to lower anterior mesopleuron; parapsidal furrows vestigial or absent; notauli absent; axillae widely separated (i.e., by width of at least one axilla), axilla fused with scutellum to narrowly separated (i.e., less than width of one axilla).

Wing: Wing veins predominantly depigmented, with distal segments reduced to vestigial lines; vein m -cu absent; vein cu -a absent.

Petiole and postpetiole: Petiolar spiracle lateral and situated slightly anteriad of petiolar node; node (viewed in profile) conical, vertex tapered, appearance of node shining and smooth; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 4:3 and 1:1; anteroventral petiolar process absent or vestigial; height ratio of petiole to postpetiole between 1:1 and 3:4; height -length ratio of postpetiole between 2:1 and 4:3; postpetiole shining, with vestigial sculpture.

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

General characters: Color light to medium brown, appendages pure brown to off-white.

Male measurements: HML 1.37-1.96 HL 0.41-0.51 HW 0.42-0.48 CeI 102-116 SL 0.10-0.19 SI 24-34 PW 0.44-0.66 (n=11).

Remarks.- Monomorium exiguum HNS ranges throughout Madagascar, but is most abundant in Toliara Province, where is it is often among the most commonly collected Monomorium HNS in sifted litter samples. Interestingly, the paler " flavescens HNS " and " bulawayense HNS " forms also occur in Madagascar, along with M. exiguum HNS sensu stricto. In the taxon faurei HNS the head is darker than the mesosoma, and the gaster is pale with darker infuscation on its basal half, as well as on the sides of the first gastral tergite. This variant, too, is quite common on Madagascar. Monomorium exiguum HNS workers from Madagascar tend to have a slightly more tapered petiolar node than their counterparts on the African mainland.

Based on comparative type material I have seen, Monomorium exiguum HNS is part of a complex that includes, at least, the exclusively African Monomorium mictile Forel HNS , Monomorium rosae Santschi HNS and Monomorium taedium Bolton HNS . An 11-segmented antenna, an elongate and flattened head capsule, weakly developed clypeal carinae, a dorsally rather flattened rather than evenly convex propodeum and the low, strongly conical form of the petiole are common to all of these taxa. Monomorium rosae HNS is placed in a different complex by Bolton (1987) on the basis of the appearance of the worker postpetiole, but in actual fact, the shape of the postpetiole in larger, darker specimens of Monomorium exiguum HNS approaches that of M. rosae HNS , if it is not identical. The degree of obliqueness seen in the posterior face of the postpetiole appears to be proportional to the size of the worker, rather than a distinct feature at the species level, let alone the species-complex level, in all three species mentioned above.

The distinction between the above four species, if indeed it truly exists, is minimal. In appearance the workers form a continuum, with the bright yellow M. mictile HNS being the smallest species and the very dark M. rosae HNS the largest. To give just one instance, the relevant measurements supplied by Bolton (1987) for M. exiguum HNS (40 specimens) and M. rosae HNS (12 specimens) certainly give this reviser pause for thought! With M. exiguum HNS in regular font, M. rosae HNS in bold, these read: TL (i.e., total length); 1.5-1.7/1.6-2.0 HL 0.36-0.42/0.42-0.50, HW 0.28-0.32/0.33-0.40 CI (=CeI) 74-80/76-82 SL 0.22-0.27/0.28-0.35 SI 74-84/85-94 PW 0.17-0.21/0.21-0.25 AL (i.e., mesosoma length) 0.36-0.44/0.42-0.56. Apart from the larger size, the only real difference that I can discern between a M. rosae Santschi HNS syntype from the Democratic Republic of Congo and large, brown specimens of M. exiguum HNS I have seen from Madagascar is the presence of faint sculpture on the lower mesopleuron in M. rosae HNS . Fresh M. rosae HNS material, which I have not seen, is said by Bolton to be "blackish-brown to black".

Monomorium mictile HNS is separated from M. exiguum HNS by Bolton (1987) on the basis of the presence or absence of erect infrahumeral setae. These are supposedly absent in M. mictile HNS and long and erect in M. exiguum HNS . In fact the setae are present, but short and appressed in M. mictile HNS . This particular character does not seem to be useful as a means of separating similar species in the M. monomorium HNS species group, at least in Madagascar. Where hundreds or even thousands of workers are available for examination, I have noticed variability in the number, length and alignment of the promesonotal setae, including differences in the length and alignment of the infrahumeral setae. This phenomenon may not be recognizable where only a few, isolated specimens are available for study. For now, I would allow for the separation of M. mictile HNS from M. exiguum HNS , as all Malagasy specimens I have seen of the latter have erect or semi-erect infrahumeral setae (albeit of different lengths). The same applies to Monomorium taedium HNS , for which I have seen three paratype workers. Apart from their somewhat larger size (HW = 0.34 mm) and lack of erect infrahumeral setae they look exactly like brown M. exiguum HNS . Interestingly, the postpetiole of the paratype specimens of M. taedium HNS is quite globose, as in smaller M. exiguum HNS .

As well as six syntypes of M. mictile HNS , I have also examined 15 syntype workers of the form Monomorium exiguum mictile HNS "sudanicum" and the lectotype worker of Monomorium minutissimus HNS , both of which taxa Bolton regarded as conspecific with M. mictile HNS . The "sudanicum" workers are certainly the same species as the M. mictile syntypes HNS and share the same uniform, bright yellow coloration, but I differ with Bolton on the identity of the headless lectotype worker of M. minutissimum HNS . Leaving aside the absence of the head (which was said by Santschi to be yellowish-brown like the gaster), the morphology of this specimen is identical with that of the M. faurei HNS type material, and has the typical coloration of this form of M. exiguum HNS . I therefore consider this taxon to be a junior synonym of M. exiguum HNS rather than M. mictile HNS . (NB. Because of the way the ant is glued on its side to its rectangle, the infrahumeral setae are not readily apparent, and may have been destroyed during the mounting process.)

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