Key to Australian Polyrhachis Subgenera

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The following key to Australian Polyrhachis subgenera is based on Kohout (2010[1]). See Definitions of habitats for definitions of the habitats used below.

1

  • Mesonotum armed with a pair of upwards and backwards curved spines; petiole distinctly higher than full height of mesosoma, terminating in a pair of hook-like spines (arboreal) (Cape York Peninsula) => Polyrhachis (single species, Polyrhachis bellicosa)
  • Mesonotum without spines; petiole lower than full height of mesosoma, dorsum armed with spines or teeth of various configurations or virtually unarmed => 2

2

  • Mesosoma completely laterally immarginate => 3
  • Mesosoma at least partly laterally marginate => 5

3

  • Small species (head length 1.25-1.65mm); dorsum of mesosoma relatively short, strongly longitudinally and transversely convex; pronotal spines reduced to acute teeth or absent; body uniformly black, highly polished => 4
  • Small to large species (head length 1.40-3.60mm); dorsum of mesosoma elongate, only weakly to moderately convex; pronotal spines relatively long, acute; colour of body variable, mostly black, but also reddish-brown or bicoloured (arboreal or lignicolous) (tropical Queensland and Northern Territory) => Myrmhopla (part) (species key)

4

  • Sides of head with longitudinal carina separating gena from ventral parts of head; propodeal spines, if present, very short; petiole scale-like, armed with four spines or teeth of various lengths and configurations, only rarely reduced to mere denticles (Polyrhachis brevinoda) (arboreal) (Northern Territory, Queensland and coastal New South Wales) => Cyrtomyrma (species key)
  • Sides of head without longitudinal carina; propodeal spines long; petiole columnar, armed with a pair of horizontal spines that conform to shape of first gastral segment and a pair of distinct intercalary teeth (arboreal) (Cape York Peninsula and north Queensland) => Myrmhopla (part) (single species, Polyrhachis mucronata)

5

  • Pronotal humeri simply rounded or, at most, bluntly angular => 6
  • Pronotal humeri armed with spines or acute teeth => 9

6

  • Dorsum of petiole usually narrowly rounded, rarely with a distinct platform (Polyrhachis thusnelda), armed with a pair of more-or-less horizontal, backwards directed or diverging, acute spines; propodeal spines rarely hook-like (Polyrhachis ammonoeides); propodeal spines always present, mostly horizontal or weakly elevated (subterranean, rarely lignicolous or lithocolous) (Australia-wide, except south, south-west and Tasmania) => Hagiomyrma (species key)
  • Dorsum of petiole variable, with two, three or four upward directed spines or teeth of various lengths and configurations, or petiole virtually unarmed; propodeal spines present or reduced to mere teeth => 7

7

  • Small species (head length 1.15-1.65mm); petiole columnar with two or three spines; body light coloured, mostly yellowish- or reddish-brown (arboreal) (tropical north Queensland and Northern Territory only) => 8
  • Small to large species (haed length 1.10-2.80mm); petiole scale-like, usually with four teeth or short spines, but rarely also with one (Polyrhachis pseudothrinax) or two (for example Polyrhachis prometheus) elongated spines or virtually unarmed with only shallow median emargination; body mostly black or rarely reddish-brown (Polyrhachis incerta) (subterranean or lignicolous, nocturnal and crepuscular foragers) (Australia-wide, including Tasmania) => Campomyrma (species key)

8

  • Petiole armed with three spines, middle spine distinctly longer than lateral spines; propodeal spines acute, distinctly elevated or virtually vertical (arboreal) (Northern Territory and north Queensland) => Myrmothrinax (species key)
  • Petiole armed with two short spines; propodeal spines reduced to short, upturned teeth (arboreal) (north Queensland) => Myrmatopa (part) (species key)

9

  • Pronotal humeri produced into broad-based short teeth with lateral margins distinctly expanded, virtually laminate; mesonotal and propodeal margins often elaborate, variously incised or with laterally dilated laminate lobes (for example Polyrhachis schoopae); body mostly broad and stocky with short appendages, generally with abundant pilosity and pubescence often masking underlying sculpturation (subterranean or rarely lignicolous) (Australia-wide, except Tasmania) => Chariomyrma
  • Pronotal humeri produced into spines or acute teeth with lateral margins distinct, but not laminate; mesonotal and propodeal margins simple, never elaborate; body elongate with relatively long appendages and only rarely with abundant pilosity and/or pubescence (for example Polyrhachis clotho) => 10

10

  • Pronotal humeri produced into long, horizontal, anteriorly directed spines; propodeal spines reduced to short, upturned teeth; petiole scale-like, armed with a pair of acute, upward directed spines and a tooth or blunt angle situated below their bases (lignicolous or terrestrial) (Cape York Peninsula) => Myrma (species key)
  • Pronotal humeri produced into horizontal or variously elevated, mostly anterolaterally directed spines or acute teeth; propodeal spines present or rarely reduced to acute teeth (Polyrhachis alphea); petiole columnar with a pair of horizontal or elevated spines => 11

11

  • Small species (head length < 1.75mm); propodeal spines reduced to acute teeth; petiole armed with two, rather long, upward directed spines (arboreal) (Cape York Peninsula) => Myrmatopa (part) (species key)
  • Larger species (head length > 1.75mm); propodeal spines always present; petiole with more-or-less flat dorsum, armed with a pair of horizontal or variously elevated spines => 12

12

  • Pronotal dorsum flat; humeri armed with acute, somewhat elevated, slender spines; propodeal spines acute, usually longer than pronotal pair, variously elevated; dorsum of petiole with rather vague, posteriorly sloping platform; dorsa of head, mesosoma and petiole with characteristic vermiculate sculpturation and short, bristle-like, brown hairs (subterranean) (Queensland) => Hirtomyrma (species key)
  • Pronotal dorsum more-or-less longitudinally and transversely convex; humeri armed with mostly horizontal, dorsally flattened, laterally or anterolaterally directed acute spines or teeth; propodeal spines mostly horizontal, but also elevated; dorsum of petiole with rather conspicuous platform (except in Polyrhachis clio); body sculpturation never vermiculate, ranging from rugose to rather smooth; silvery or rich golden pilosity and pubescence in various densities over most body surfaces (lignicolous or rarely lithocolous) (tropical and coastal temperate Australia, except central and southern regions) => Hedomyrma


Definitions of habitats

Based on Robson & Kohout (2007[2]).

Subterranean
In the soil with or without any cover such as rocks or fallen logs.
Terrestrial
On the ground beneath logs and stones, in or between grass stems.
Lignicolous
Within the cavities of living or dead plants, including hollow stems, bamboo internodes, the base of ferns in trees, cavities under bark, or within myrmecophyte plants.
Lithocolous
On or within rock crevices.
Arboreal
Among leaves or twigs, either against a single surface such as a trunk or between adjacent surfaces such as leaves.

References

  1. Kohout, R.J. 2010. A review of the Australian Polyrhachis ants of the subgenera Myrmhopla Forel and Hirtomyrma subgen. Nov. (Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum — Nature 55(1), 167-204.
  2. Robson, S.K.A. & Kohout, R.J. 2007. A review of the nesting habits and socioecology of the ant genus Polyrhachis Fr. Smith. Asian Myrmecology 1, 81–99.