Strumigenys emarginata group

Strumigenys emarginata group Bolton (2000)

Worker Diagnosis
Mandibles in full-face view and at full closure triangular to elongate triangular, with serially dentate masticatory margins that usually engage throughout their visible length; sometimes apices of basal most teeth may meet but not fully interlock. In profile only extreme apex of mandible down-curved. In ventral view outer margin of mandible without a prebasal inflected angle. MI 6-19.

Dentition. Basally with a dental row of 5 narrowly triangular to spiniform teeth, distal to which are 2 smaller teeth, 4 minute denticles and a small apical tooth, giving a total dental count of 12.

Basal lamella of mandible a high narrow triangle that may be acute or truncated apically, or a high narrow rectangle with concave sides; not visible in full-face view when mandibles fully closed.

Labrum terminates in a pair of elongate triangular to conical narrow lobes.

Clypeus with anterior margin usually concave in full-face view, varying from evenly shallowly concave across the entire width to deeply concave medially; only rarely more or less transverse. In ventral view the lateral clypeal margins extend well beyond the outer margins of the fully closed mandibles through the basal third or more of their length.

Clypeal lateral and anterior margins with a continuous fringe of spatulate to spoon-shaped hairs that curve anteriorly on the lateral margins and toward the midline on the anterior margin. Dorsum of clypeus without standing hairs but usually with anteriorly directed minute to conspicuous hairs that are narrowly spatulate to suborbicular and are decumbent to appressed.

Preocular carina visible in full-face view but sometimes very narrow behind level of frontal lobes.

Ventrolateral margin of head between eye and mandible angulate to sharply marginate, straight to extremely shallowly concave. Postbuccal impression usually shallow but distinct, sometimes broad.

Cuticle of side of head within scrobe densely punctate or reticulate-punctate.

Scape short to moderate, SI 48-83, dorsoventrally flattened, the dorsum and ventre converging anteriorly so that the leading edge is a flange or even a thin lamella. Ventral surface of scape behind the leading edge usually distinctly concave.

Leading edge of scape with a row of spatulate, remiform or spoon-shaped hairs, some or all of which are curved or inclined toward the base of the scape.

Pronotum without a median longitudinal carina.

Propodeum bidentate to bispinose, lamella on declivity usually vestigial to absent but sometimes developed.

Spongiform appendages of petiole and postpetiole large to massively developed. Base of first gastral sternite in profile without a pad or crest of dense spongiform tissue.

Pilosity. Very variable through the group, often with clavate, spatulate, spoon-shaped, suborbicular or other bizarre setae present, but never with flagellate hairs. Pronotum usually without humeral hairs, but if present the hair is not distinctly different in structure or size from other hairs on the dorsal alitrunk. Some species with extremely reduced pilosity. Ground-pilosity of head and alitrunk sometimes absent but generally of small curved spatulate to spoon-shaped hairs. Dorsal (outer) surfaces of middle and hind tibiae without elongate freely projecting hairs.

Sculpture. Fine to absent; commonly the dorsum of the head behind the clypeus and promesonotum reticulate-punctate, the latter area sometimes almost smooth or with feeble longitudinal costulae, but never with coarse rugose or sulcate sculpture.

Previously described species of this endemic Afrotropical group were fully discussed by Bolton (1983), so only minimal diagnostic notes are repeated here. The group as currently defined includes the mandibularis-group and emarginata-group of the 1983 survey. The only character separating the original groups was antennomere count, with 4 segments in the former and 6 in the latter. It is now apparent that the change from 6 to 4 segments, by loss of the two reduced segments between the first funicular segment and the club, has been achieved within groups on a number of separate occasions. The character is consequently of relatively little importance in higher taxonomy, but useful in identification.

Five complexes of closely related species occur within the group, with the following diagnoses.

mandibularis complex
Strumigenys fulda, Strumigenys mandibularis, Strumigenys ninda, Strumigenys tigrilla

Antenna 4-segmented. Anterior clypeal margin narrow and deeply concave. Propodeal tooth subtended by a broad lamella. Standing hairs absent or very sparse on dorsal surfaces of head and body. CI 73-88, MI 6-12, SI 48-54.

chyatha complex
Strumigenys behasyla, Strumigenys cavinasis, Strumigenys chyatha, Strumigenys impidora, Strumigenys sharra

Antenna 6-segmented. Anterior clypeal margin shallowly to deeply concave. Dorsa of head and alitrunk without standing hairs; first gastral tergite without, or with sparse short, standing hairs. Cephalic dorsum usually with appressed scale-like or suborbicular hairs present (absent only in impidora, perhaps secondarily). Pronotal sculpture fine and dense, usually of minute close-packed longitudinal striolae upon a granular surface. CI 56-67, MI 7-16, SI 63-78.

emarginata complex
Strumigenys emarginata, Strumigenys exunca, Strumigenys noara, Strumigenys robertsoni, Strumigenys subsessa

Antenna 6-segmented. Anterior clypeal margin transverse to broadly shallowly concave. Mediobasal area of first gastral tergite depressed, concave, base of sclerite with a distinctly dented appearance and the basigastral costulae radiating from each side of the depression. First gastral tergite in dorsal view with suture line between limbus and sclerite proper distinctly arched-concave on each side of the midline. Eye large, its maximum diameter distinctly greater than the maximum width of the scape, with 5-7 ommatidia in the longest row and its outer curvature usually visible in full-face view. Pilosity of head and alitrunk variable but first gastral tergite with numerous standing long hairs. CI 59-65, MI 15-18, SI 70-83.

hensekta complex
Strumigenys hensekta

Antenna 6-segmented. Anterior clypeal margin transverse. Densely hairy, with numerous standing simple hairs on cephalic dorsum (from about highest point of vertex to occipital margin), on promesonotum, and on first gastral tergite. Pronotal humerus with a laterally projecting stout hair. Pleurae and side of propodeum mostly or entirely reticulate-punctate. CI 66-69, MI 17-18, SI 59-65.

truncatidens complex
Strumigenys datissa, Strumigenys gatuda, Strumigenys truncatidens

Antenna 6-segmented. Anterior clypeal margin broadly shallowly concave. Sparsely hairy, with few to many standing hairs on cephalic dorsum behind highest point of vertex, none on dorsal pronotum, 1-3 pairs on mesonotum, numerous on first gastral tergite. Pleurae and side of propodeum mostly or entirely smooth. CI 70-77, MI 10-18, SI 58-67.