Strumigenys excisa group

Strumigenys excisa group Bolton (2000)

Species

Neotropical

Strumigenys asaphes
Strumigenys azteca
Strumigenys dontopagis
Strumigenys excisa
Strumigenys longinoi
Strumigenys prex
Strumigenys rogata
Strumigenys superstes Booher & Uhey 2020
Strumigenys turpis

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.

Notes

Booher & Uhey (2020) included the following regarding this species group (the text following this paragraph is from Bolton 2000): All 10 previously described species are endemic to Neotropical/Panamanian forests in Central America and southern Mexico. Collections of the excisa group are sparse and almost exclusively from samples of leaf litter in nondisturbed tropical forests (Bolton 2019; García-Martínez et al. 2015, 2017; Jack Longino personal communication). Two species, S. turpis and S. asaphes, are known from just a few specimens and several others (Strumigenys augustandrewi, Strumigenys dontopagis, Strumigenys erikae, Strumigenys longinoi, and S. prex) seem to be restricted to specific rainforest preserves. S. rogata and S. excisa are the most frequently collected species and have the largest ranges, from Costa Rica to southern Mexico with S. rogata having the northern-most record with a specimen collected in a subtropical montane forest ~200 km east of Mexico City (20.0°N, -97.5°W). Although several species in the excisa group have been collected in cool montane forests, climatic records from geographic collection sites of excisa group species reveal S. superstes inhabits a more extreme cold and dry region.

This mainly Central American group is defined by the structure of the postpetiole, which is autapomorphic, combined with extensive reduction or even total loss of spongiform appendages. These features, combined with the form of the mandibles, labrum and head capsule, make identification of the group quite easy. The species within the group can be organized into the following species-complexes.

azteca-complex

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

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

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.

Strumigenys longinoi

not placed to a complex

Described in 2020, Strumigenys superstes was not placed in an excisa species-group complex.

References