Strumigenys excisa group

Strumigenys excisa group Bolton (2000)

Worker Diagnosis
Mandibles in full-face view and at full closure short triangular, serially dentate, margins engage throughout their visible lengths. In profile dorsal margin of mandible distal of clypeus downcurved. In ventral view outer margin of mandible passes through a shallow prebasal curve, without a marked prebasal inflected angle. MI 16-22.

Dentition. Counting from the base, mandible with 7-9 stout conical teeth that may be somewhat recurved; teeth approximately the same size or size increases markedly from tooth 1 to tooth 6 or 7. Apically 2-3 denticles or a slightly enlarged apical tooth may be present; total dental count 10-12.

Basal lamella large, broad basally and at least as tall as any of the teeth, apically tapering slightly and its median free margin rounded or truncated; not visible or with its anterior margin just visible in full-face view with mandibles fully closed. Basal tooth follows lamella without a diastema.

Labrum with lobes broad, elongate and flattened, either spatulate or bluntly triangular, separated by a marked U- or V-shaped impression. Lateral margins of lobes either evenly divergent or divergent to just beyond midlength then convergent to the apex.

Clypeus with anterior margin approximately transverse to broadly and shallowly concave across its width; anterolateral angles rounded and lateral margins weakly convex. Outer margins of fully closed mandibles intersect anterior clypeal margin at or mesad of the anterolateral angles.

Clypeal dorsum hairless, or with minute appressed pubescence or fine simple hairs that may be subdecumbent or suberect, the lateral margins with or without projecting fine simple hairs.

Frontal lobes and frontal carinae expanded laterally, fused with the lateral expansions of the clypeus so that the dorsolateral margin of the head is continuous from front to back (usually a minute indentation at j unction of clypeus and frontal lobe).

Preocular carinae not visible in full-face view, concealed by lateral expansion of frontal lobes and frontal carinae.

Ventrolateral margin of head sharply marginate in front of eye, the margination concave and sometimes terminates anteriorly in an angle or small tooth. Postbuccal impression shallow, or narrow and deeply incised.

Cuticle of side of head within antennal scrobe smooth and shining.

Scape very short to short, SI 44-60, not markedly dorsoventrally flattened, with a shallowly convex leading edge and without a pronounced subbasal angle.

Leading edge of scape hairless or with simple apically directed hairs that may be decumbent or elevated; without spatulate or spoon-shaped hairs and without hairs that are directed or curved toward the base of the scape.

Spongiform appendages. Petiole without trace of ventral spongiform tissue. Petiole node in dorsal view with lateral lobes varying from absent to moderate in size; when present often lamellate rather than spongiform. Postpetiole without ventral lobes but lateral lobes varying from small dentiform projections to moderate aliform lobes that may be thin and lamellate rather than spongiform; no posterior spongiform collar. Base of first gastral sternite in profile without trace of spongiform tissue.

Postpetiole in dorsal view very distinctly broadly U-shaped or V-shaped, with a deeply concave anterior margin and convex posterior margin.

First gastral sternite in profile with longitudinal outline convex or concave from midlength to base; basally the stemite transversely shallowly convex to markedly concave on each side of the midline to the lateral margin; the tergite overhangs the flattened stemite laterobasally.

Pilosity. Curved to flagellate fine simple hairs absent to abundant on dorsal surfaces of head and body; dorsolateral margins of head with or without freely laterally projecting hairs; pronotum with or without humeral hair.

Sculpture. Dorsum of head behind clypeus never covered with reticulate-punctate sculpture. Pleurae and side of propodeum unsculptured. Basigastral costulae usually fine and scratch-like, generally longer dorsolaterally than mediodorsally and frequently effaced medially.

azteca-complex
Strumigenys azteca, Strumigenys prex, Strumigenys rogata, Strumigenys turpis

In these four species the inner cuticular margins of the mandibles, from which the teeth arise, diverge anteriorly and form an inverted V-shape from base to apex when the mandibles are fully closed (full-face view). Counting from the base teeth 1 to 6 increase markedly in length. The divergence of the inner margins allows the lengthening teeth to remain interlocked at full closure rather than causing them to overlap. Standing pilosity is extremely sparse to moderately dense. The first gastral sternite is markedly dorsoventrally compressed basally. In profile the longitudinal outline of the sternite is depressed or concave basally for up to half of its length and is transversely concave basally from the midline to the lateral margin on each side.

The four species currently recognised in this complex are closely related and all are represented by relatively sparse material.

excisa-complex
Strumigenys asaphes, Strumigenys dontopagis, Strumigenys excisa

In these three species the inner cuticular margins of the mandibles, from which the teeth arise, are roughly parallel at full closure. The basal tooth is small, arising from near the base of the anterior margin of the basal lamella. Second tooth is larger, intermediate in size between teeth 1 and 3. Teeth 3-7 are large and conical, slightly recurved; teeth 4-6 are the largest on the margin. Distal of tooth 7 there are two small teeth and a slightly larger apical tooth, to give a total dental count of 10. Fine erect pilosity is abundant on all dorsal surfaces of the head and body, and many fine hairs freely project laterally from the dorsolateral margins of the head. In two of the species (Strumigenys dontopagis, Strumigenys excisa) the longitudinal outline of the first gastral sternite in profile is evenly convex, but in asaphes it is markedly concave in its basal third.

S. excisa was the type-species and sole member of the genus Borgmeierita Brown (1953a). This was later synonymised with Glamyromyrmex by Brown (1973a); both names have now been abandoned (Bolton, 1999).

S. asaphes forms a link between the species of the azteca-complex and those of the excisa-complex as it combines the gastral structure of the first with the dentition of the second.

longinoi-complex
Strumigenys longinoi

The single species included here is relatively large (see measurements) and has a remarkably dorsoventrally flattened head, reminiscent of that seen in the substricta-group. On the mandible the teeth are roughly the same size from 1 (basal) to 7; the inner cuticular margins from which the teeth arise are approximately parallel at full closure. Dorsa of head, alitrunk, waist segments and gaster completely lack standing hairs. The longitudinal outline of the first gastral sternites in profile is convex from the midlength to the base.