Strumigenys arnoldi group

Strumigenys arnoldi group Bolton (2000)

Species

Afrotropical

Malagasy

Worker Diagnosis

Afrotropical

Apical fork of mandible usually without intercalary teeth (a single species with an intercalary denticle, Strumigenys katapelta). Right mandible with two preapical teeth (a single species with one), the proximal longer than the distal. Left mandible usually with two preapical teeth but some species (dextra-complex) with one. MI 26-77.

Scape rarely subcylindrical, usually weakly to very markedly dorsoventrally flattened. Scape usually relatively short, SI 52-77, but elongate in some species, SI 80-90. Eyes very small or vestigial, maximum eye diameter much less than maximum width of scape.

Upper scrobe margin with a narrow to broad laminate border.

Ventrolateral margin of head without trace of a preocular notch, the margin continuous in front of the eye. Ventral surface of head without a preocular transverse groove but postbuccal groove distinct.

Ventral surface of petiole usually with a conspicuous spongiform strip or curtain, only rarely otherwise; spongiform lobes of postpetiole present but first gastral sternite without a basal spongiform pad.

Pilosity. Pronotal humeral hair absent or present. Apicoscrobal hair absent; upper scrobe margin fringed by a continuous row of small hairs. Cephalic ground-pilosity usually conspicuous and scale-like to spoon-shaped, at least on anterior half of dorsum. Cephalic dorsum with 0-6 standing hairs, usually with a transverse row of 4 near occipital margin and a pair close to highest point of vertex; variously reduced in individual species. Mesonotum usually with a single pair of standing hairs (rarely more). First gastral tergite with simple to remiform hairs; flagellate hairs always absent from gaster.

Sculpture. Head and dorsal alitrunk reticulate-punctate, pronotal dorsum frequently with longitudinal or oblique rugulae or costulae. Pleurae and side of propodeum smooth and gaster unsculptured except for basigastral costulae (except in Strumigenys didyma). Members of the arnoldi-group are best diagnosed by the complete absence of a preocular notch in the ventrolateral margin of the head and consequent lack of a ventral preocular transverse groove that extends across the ventral surface. Coupled with this, the eye is very small, and subappressed to appressed scale-like or spoon-shaped ground-pilosity, at least on the anterior half of the head, occurs in most species of the group.

Malagasy

Apical fork of mandible with 2 teeth; always with one long preapical tooth. In some species a second (distal) preapical tooth or denticle is present, between the long (proximal) preapical tooth and the apicodorsal tooth; when present the distal preapical tooth is often weaker on the left mandible than on the right. Mandible in full-face view short (MI 27 - 47), narrow, linear and outcurved in full-face view; the dorsum, proximal of the basalmost tooth, slightly concave.

Antenna usually 6-merous with funicular segments 2 and 3 small and often difficult to discern, but antenna 4-merous in Strumigenys micrans, Strumigenys schuetzi, Strumigenys lutron, Strumigenys levana.

Leading edge of scape a dorsoventrally flattened convex lamella.

Eye very small or vestigial, usually with 4 or less ommatidia.

Upper scrobe margins in full-face view widely divergent behind the frontal lobes.

Ventrolateral margin of head without trace of a preocular notch, the margin continuous in front of the eye. Ventral surface of head without a preocular transverse groove but postbuccal groove is distinct.

Promesonotum flat to slightly convex dorsally and bluntly marginate dorsolaterally.

Spongiform appendages of petiole usually well developed into a ventral curtain (narrow strip in Strumigenys abdera); lateral lobes present. Postpetiole with lateral and ventral lobes. Lamella on propodeal declivity usually well developed into a wide strip below the triangular propodeal spines (narrow in Strumigenys charino, micrans, Strumigenys mola).

Pilosity. Pronotal humeral hair absent or present. Apicoscrobal hair absent. Head with curved spatulate to spoon-shaped or orbicular hairs present on dorsum of head behind clypeus at least on anterior half (absent in abdera), anterior clypeal margin, lateral clypeal margin, upper scrobe margin (curved anteriorly) (short, simple appressed hairs in abdera), and leading edge of scape. Dorsum of head without erect hairs or with a transverse row of 4 hairs close to the occipital margin (abdera, Strumigenys alapa, charino, levana, lutron, Strumigenys manga, micrans, mola). Mesonotum without erect hairs, or with one pair on the mesonotum (abdera, alapa, lutron, manga, micrans, mola) or with two pairs (levana). Dorsal surface of postpetiole, and gaster with short filiform to narrowly clavate hairs; entire body usually lacking flagellate hairs.

Sculpture. Fine dense reticulate-punctate to reticulate-granulate sculpture blankets the entire dorsum of the head; the pronotum reticulate-punctate and occasionally with longitudinal costulae; remainder of the dorsal alitrunk reticulate-punctate (propodeum not reticulate-punctate in manga); petiole with dense reticulate-punctate sculpture or with faint reticulate-punctate sculpture that is almost effaced. Gaster unsculptured except for basigastral costulae.

Glands. Scape gland absent (Strumigenys bathron, charino, Strumigenys dolabra, lutron, manga, micrans, mola, schuetzi, toma) or visible as a elongate patch near apex of ventral scape (abdera, alapa, Strumigenys heliani, levana). Femoral and tibial gland bullae absent. Gland at base of calcar conspicuous. Tarsal glands absent (alapa, bathron, toma) or visible on at least first three tarsi of fortarsi, decreasing in size from basitarsus where it is elongate to the third tarsal segment where it is oval. Mesopleural gland visible and set in a circular notch.

Notes

Afrotropical

The group contains 20 species in the Afrotropical region, divisible into four complexes.

arnoldi complex

Left mandible with two preapical teeth. Funicular segments 2 and 3 small but obvious, not fused together nor fused to segment 4, the funiculus distinctly with 5 segments. Combined length of funicular segments 2 and 3 more than half the length of segment 4 (the penultimate segment). Scapes moderately to strongly dorsoventrally flattened and short to moderate, SI 52-79. Head averaging broader and mandibles shorter, CI 70-97, MI 34-58.

dextra complex

Left mandible with only one preapical tooth (the proximal); right mandible usually with 2 preapical teeth (one species with 1) but the distal small and sometimes concealed by the opposing apicodorsal tooth at full closure. Funicular segments 2 and 3 small but obvious, not fused together nor fused to segment 4, the funiculus distinctly with 5 segments. Combined length of funicular segments 2 and 3 more than half the length of segment 4 (the penultimate segment).

nimbrata complex

Left mandible with two preapical teeth. Funicular segments 2 and 3 extremely reduced, partially or entirely fused together and partially fused to segment 4 so that the funiculus appears to have only 3 segments in total, the second of which is minute; combined length of funicular segments 2 and 3 less than half the length of segment 4 (the penultimate segment)

havilandi complex

Left mandible with two spiniform preapical teeth. Funicular segments 2 and 3 small but obvious, not fused together nor fused to segment 4, the funiculus distinctly with 5 segments. Combined length of funicular segments 2 and 3 more than half the length of segment 4 (the pen ultimate segment). Scapes slender and relatively long, SI 80-90. Head averaging narrower and mandibles longer, CI 67-74; MI 52-77.

Malagasy

In the Malagasy region members of this group are most similar to species of the emmae group, adsita group and dexis groups but differ in mandibular dentition and hairs on upper scrobe margin. The apicoscrobal hair is absent (present in emmae); apical fork of mandible is never composed of 3 spiniform teeth as in adsita-group and mandibles are symmetric, each with either with 3 or 4 teeth (asymmetric in dexis-group).

In addition, the arnoldi-, emmae-, and adsita-groups can be distinguished from the dexis-group by the following characters: eye always small to minute (usually with 4 or less ommatidia) and the lower scrobe margin rounded, never forming a sharp ridge with ventral surface of head. In the dexis-group the eyes are usually conspicuous, never with 4 or less ommatidia, but if eyes small then the lower scrobe margin forms a sharply marginate ridge with ventral surface of head.

The arnoldi-group is also very speciose in the Afrotropical region (see there). The group diagnosis above is somewhat modified from the Afrotropical, to give a best representation of the Malagasy fauna. Within this region members of the group fall into four discrete complexes of related species.

abdera complex

Right and left mandible each with a spiniform proximal preapical tooth and a smaller distal preapical tooth or denticle; distal preapical is weakest on left mandible and may be a minute denticle. Antenna with 6 segments.

alapa complex

Right and left mandible each with one spiniform preapical tooth, without preapical denticles more distally. Antenna with 6 segments.

lutron complex

Right and left mandible each with a spiniform proximal preapical tooth and a smaller distal preapical tooth or denticle; distal preapical is weakest on the left mandible. Antenna with 4 segments.

schuetzi complex

Right and left mandible each with one spiniform preapical tooth, without preapical denticles more distally. Antenna with 4 segments.

Strumigenys schuetzi

References

Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028.