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Ants of the subfamily Pseudomyrmecinae: tabular key to species groups of Pseudomyrmex

About 85% of the 200-odd species in the ant genus Pseudomyrmex can be placed reliably within one of nine major species groups (Ward, 1989). This tabular key summarizes the salient worker characteristics of each of these groups. The table should permit the assignment of most worker-based samples to a species group, but bear in mind that there is a residue of taxonomically isolated species that will not fit the diagnosis of any group. The characters used in this table are explained after the table.

Species group Palp
formula(e)
Number of
teeth on
masticatory
margin of
mandible
Median clypeal
lobe:
laterally rounded
or angulate
Pilosity on
mesosoma:
common
(MSC > 10)
versus
sparse
(MSC < 8)
Tibial pilosity:
common
(HTC + MTC > 10)
or
sparse
(HTC + MTC < 8)
Eye size:
short
(REL 0.36-0.46)
versus
elongate
(REL 0.48-0.68)
Other
gracilis group 6,4 7-10 rounded1 common3 common3 elongate pronotum laterally margined
tenuis group 6,4 6 rounded sparse sparse elongate metanotal groove absent
sericeus group 6,4; 5,4 8-10 rounded sparse sparse elongate silky (sericeous) integument
pallens group 6,4 5-6 rounded usually sparse sparse variable
viduus group 6,4; 5,3; 4,3 5-7 usually rounded2 common common4 short broad petiole, PWI > 0.70
oculatus group 6,3; 5,3 5-6 rounded common usually sparse elongate tectiform clypeal lobe
subtilissimus group 6,3 5 rounded sparse sparse elongate frontal carinae elevated
pallidus group 5,3; 4,3 5 angulate sparse sparse variable
ferrugineus group 5,3; 4,3 6 variable common sparse short inhabiting swollen-thorn acacia

1 Somewhat angulate in P. laevigatus
2 Angulate in P. malignus and P. tachigaliae
3 Except P. simulans
4 Except P. tachigaliae

Explanation of characters

The palp formula is the number of maxillary palp segments, followed by number of labial palp segments. In some specimens these segments can be counted in situ; in other instances dissection and slide preparation are necessary.

Number of teeth on the masticatory margin of mandible. This refers to the median number of teeth on the masticatory (biting) margin, within a series of workers from a given nest or population. Mandibular dentition generally shows little variation within a species, but deviations from the “typical” number of teeth occur occasionally. For more details on mandible morphology and terminology see Figure 1 below, which illustrates a mandible bearing six teeth on the masticatory margin.

Median clypeal lobe. The two conditions being contrasted here are an anterolateral margin that is (i) rounded or bluntly angled, versus (ii) sharply angulate.

Mesosomal and tibial pilosity. MSC, MTC and HTC are the number of standing hairs (setae) on the mesosoma dorsum (as seen in profile), external face of mesotibia, and external face of metatibia, respectively. For further details about setal counts see “Use Of Morphometric Measurements”

Eye size. REL is an index of eye size, calculated as EL/HL (eye length/head length). For further details on the measurement of EL and HL see “Use Of Morphometric Measurements”.

Figure 1. Worker, right mandible.

Literature Cited

  • Ward, P.S. 1989. Systematic studies on pseudomyrmecine ants: revision of the Pseudomyrmex oculatus and P. subtilissimus species groups, with taxonomic comments on other species. Quaestiones Entomologicae 25:393-468.

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