Pheidole gracilis

The species was collected at 1300 m in elevation, in montane rainforest. Nests were located in dead branches above ground.

Identification
Salata and Fisher (2020) - A member of the Pheidole sikorae species group. Moderately large species. Major: Head in full-face view sub-oval and not widening posteriorly, with anterior and posterior sides slightly convex, in lateral view sub-oval; ventral and dorsal faces convex; sides of the head with dense, short, decumbent to suberect pilosity; medial part of frons with moderately thick, longitudinal, interrupted, and moderately dense rugae, interspaces rugulate, rugae directed slightly outward on posteromedial part; occipital lobes predominantly smooth, only anterior part with indistinct, dense, thin, and longitudinal rugae; area posterolateral from eyes with indistinct, dense, thin, and longitudinal rugae, posteriormost part smooth; scape, when laid back, exceeding the midlength of head by approximately two-fifths of its length; inner hypostomal teeth distinct, low, closely spaced, triangular, with rounded apex directed upward; outer hypostomal teeth dentate, wider and higher then inner teeth; inner and outer hypostomal teeth closely spaced and connected by indistinct concavity; mesosoma distinctly foveolate; promesonotum with additional sparse and moderately thick, irregular to transverse rugae on dorsum; katepisternum with smooth notch; body yellowish orange. Minor: Head foveolate; vertex with additional, short, and transverse rugulae; area posterolateral from eyes with weaker sculpture that appears smooth; scape, when laid back, exceeding the posterior head margin by two-fifths of its length; promesonotum low and moderately long; promesonotal groove present; propodeal spines moderately large with narrow base; mesosoma foveolate; katepisternum with smooth notch; body yellow to orange.

Pheidole gracilis is a member of a group of species characterised by distinctly reduced head sculpture in major workers with occipital lobes entirely or predominantly smooth, area posterolateral from eyes partially or entirely smooth and shiny or with reduced sculpture and smooth notches. The group consists of four species: Pheidole litigiosa, Pheidole masoandro, P. gracilis, and Pheidole tampony Pheidole gracilis is known only from Parc National Montagne d'Ambre in Antsiranana and its distribution doesn't overlap with other members of this group. Morphologically the species is most similar to P. litigiosa, known from the vicinity of Antananarivo, and P. masoandro, described from Anosyenne Mts. in Toliara. Its major workers can be easily separated from both of those taxa based on more developed head sculpture with occipital lobes anteriorly covered by indistinct, dense, thin, and longitudinal rugae and distinctly foveolate promesonotum; minor workers can be separated based on foveolate mesosoma and low and long promesonotum. Minor workers of P. gracilis are similar to minors of P. tampony and Pheidole befotaka but can be separated based on more developed head sculpture with additional, short, and transverse rugulae on vertex and area posterolateral from eyes with weak but distinct sculpture and lacking smooth notches.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Nomenclature

 * . Pheidole gracilis Salata & Fisher, 2020: 64, figs. 30A–F, 63L, 65L (w.) MADAGASCAR.

Worker
Major (N = 8): HL: 1.22-1.32 (1.27); HW: 1.22-1.33 (1.27); SL: 0.72-0.82 (0.77); EL: 0.16-0.19 (0.17); WL: 1.08-1.22 (1.15); PSL: 0.16-0.21 (0.18); MTL: 0.76-0.83 (0.79); PNW: 0.48-0.53 (0.51); PTW: 0.14-0.17 (0.16); PPW: 0.3-0.37 (0.33); CI: 97.3-103.5 (99.8); SI: 56.7-63.3 (60.7); PSLI: 12.8-16.9 (14.6); PPI: 43.1-55.8 (49.0); PNI: 38.8-41.4 (39.8); MTI: 59.3-65.7 (62.1).

Head. In full-face sub-oval, not widening posteriorly, with anterior and posterior sides slightly convex. In lateral view sub-oval; ventral and dorsal faces convex; inner hypostomal teeth visible. Sides of the head with dense, short, decumbent to suberect pilosity; whole head with dense, long, decumbent to erect pilosity. Medial part of frons with moderately thick, longitudinal, interrupted, and moderately dense rugae, interspaces rugulate, rugae directed slightly outward on posteromedial part; lateral sides with thick, dense, and longitudinal rugae with distinctly rugulate interspaces. Occipital lobes predominantly smooth, only anterior part with indistinct, dense, thin, and longitudinal rugae. Area posterolateral from eyes with indistinct, dense, thin, and longitudinal rugae, posteriormost part smooth and shiny. Gena with relatively sparse and thick longitudinal rugae and smooth to indistinctly rugulate interspaces. Centre of clypeus smooth and shiny, lateral sides with indistinct rugulae; median notch present, moderately wide, and shallow; median longitudinal carina absent; lateral longitudinal carinae absent. Scape, when laid back, exceeding the midlength of head by two-fifths of its length; pilosity subdecumbent to erect. Inner hypostomal teeth distinct, low, closely spaced, triangular, with rounded apex directed upward; outer hypostomal teeth dentate, wider and higher than inner teeth; inner and outer hypostomal teeth closely spaced and connected by indistinct concavity. Mesosoma. In lateral view, promesonotum short, angular, and moderately low, posterior mesonotum moderately steep, mesonotal process indistinct, tubercle-like; promesonotal groove absent; metanotal groove absent; propodeal spines moderately long, with narrow base and acute apex; humeral area weakly produced. Surface shiny and distinctly foveolate; promesonotum with additional sparse and moderately thick, irregular to transverse rugae on dorsum; katepisternum with smooth notch. Pilosity sparse, long, and erect. Petiole. Shiny with sparse foveolae; node finely foveolate, triangular, with rounded and thick apex, in rear view node dorsoventrally slightly concave; pilosity moderately sparse and erect. Postpetiole. Shiny and foveolate; dorsum with reduced sculpture and smooth notch; in dorsal view oval, lateral margins medially with two wide and dentate projections; pilosity long, moderately sparse, and erect. Gaster. Shiny and smooth; pilosity moderately sparse, moderately long, and erect. Colour. Yellowish orange with yellow legs.

The following characters are found in most Pheidole sikorae species-group majors in Madagascar (Salata and Fisher 2020b). These characters also occur in , except for any differences noted in the paragraph above. Dorsal face of head in lateral view not depressed posteriorly; antennal sockets shallow; frontal lobes absent; head in full-face view with distinct median concavity; antenna 12-segmented, with 3-segmented club; masticatory margin of mandible with large, stout apical and preapical teeth, followed by a long diastema and then a short and crenulate tooth just before the rounded basal angle; outer surface of mandible mostly smooth and shining, sometimes with weak and sparse foveolae; antennal scrobes absent; promesonotum strongly convex, well above the level of propodeum; petiolar peduncle with small horizontal lobes on its basal part; postpetiole short with slightly convex dorsum; petiolar peduncle without horizontal lobes on its basal part; body unicolourous.

Minor (N = 10): HL: 0.65-0.71 (0.69); HW: 0.55-0.58 (0.56); SL: 0.69-0.74 (0.71); EL: 0.12-0.14 (0.13); WL: 0.84-0.89 (0.86); PSL: 0.1-0.12 (0.11); MTL: 0.58-0.66 (0.61); PNW: 0.36-0.4 (0.38); PTW: 0.07-0.1 (0.09); PPW: 0.15-0.19 (0.16); CI: 118.3-123.9 (121.5); SI: 123.7-132.8 (126.8); PSLI: 15.0-17.8 (16.3); PPI: 49.7-66.0 (57.0); PNI: 65.1-69.6 (67.4); MTI: 103.8-112.7 (108.9).

Head. Cephalic margin slightly convex. Pilosity relatively sparse, moderately long, decumbent to subdecumbent. Sculpture shiny and foveolate; vertex with additional, short, and transverse rugulae; area posterolateral from eyes with weaker sculpture that appears smooth; antennal sockets with few thick, curved outward rugae and foveolate interspaces. Clypeus with median longitudinal carina absent; two lateral longitudinal carinae absent. Scape, when laid back, exceeding the posterior head margin by two-fifths of its length; pilosity dense, suberect to erect. Mesosoma. In lateral view, promesonotum low and moderately long, arched; promesonotal groove present; metanotal groove distinct; propodeal spines moderately large with narrow base, triangular. Sculpture shiny and foveolate; katepisternum with smooth notch. Pilosity very sparse, moderately long, and erect. Gaster. With sparse, erect pilosity. Colour. Orange to yellow.

The following characters are found in most Pheidole sikorae species-group minors in Madagascar (Salata and Fisher 2020b). These characters also occur in , except for any differences noted in the paragraph above. Antennal sockets shallow; frontal lobes absent; occipital carina absent; head in full-face view oval, posterior and anterior of eyes convex; antenna 12-segmented, with 3-segmented club; humeral area not developed; clypeus smooth and shiny, its anterior margin regularly convex; promesonotum well above the level of propodeum; petiole smooth, with node moderately low, triangular, and small, with few short, erect setae; petiolar peduncle with ventral face slightly convex; postpetiole smooth, short, low, and slightly convex, with few short, erect setae; gaster smooth and shiny; body unicolourous.

Type material
Holotype. Madagascar. 1 major worker; Antsiranana; Parc National Montagne d'Ambre, 12.2 km 211°SSW Joffreville; -12.59639, 49.1595; alt. 1300 m; 2 Feb 2001; Fisher et al. leg.; montane rainforest, ex dead branch above ground; BLF02825; CASENT0403308, middle specimen on the pin. Paratypes. 6w., 4s.; same data as for holotype, CASENT0403307, CASENT0872252, CASENT0403309, CASENT0403310 (CASC,, ).

Etymology
Latin for slender in reference to body sculpture.