Hagiomyrma

This is currently a subgenus of Polyrhachis. Kohout (2013) - Hagiomyrma can be considered the most ‘Australian’ subgenus of Polyrhachis, with almost all of its constituent species endemic to Australia. Only four of the presently recognised 48 species were originally described from beyond the Australian mainland, with three of them, P. denticulata Karavaiev, P. schenkii Forel and P. semiobscura Donisthorpe, reported from Australia in recent years (Kohout & Taylor 1990: 514, 519), while the fourth species, P. metella Fr. Smith, appears to be endemic to New Guinea. The distributions of most Hagiomyrma species are centred on coastal Queensland, however, some (e.g. P. ammonoeides Roger, P. pilbara ) occur only in north-western Western Australia, while the ranges of several others (e.g. P. crawleyi Forel, P. schenkii Forel) extend along the northern Australian coastline from the Kimberley region in the west to Cape York Peninsula in the east. Only four species follow the eastern Australian seaboard from Queensland south to central New South Wales, with two (P. ammon and P. semiaurata Mayr) reaching as far south as Victoria and one of them (P. ammon) extending westwards to the Australian Capital Territory.

Identification
Kohout (2013) - Hagiomyrma is one of the relatively well-defined subgenera of the genus Polyrhachis. A marginate mesosomal dorsum, mostly rounded pronotal humeri and more-or-less horizontal, posteriorly directed propodeal spines, make most members of this subgenus easily recognisable.

Key to Polyrhachis Hagiomyrma group species

Biology
Most species seemingly prefer open Eucalyptus forests and savannah woodlands. However, two new species were most recently recorded from the spinifex grasslands of central Australia, with one from the Tanami Desert and the other from the MacDonnell Ranges. In stark contrast, two species, P. diversa and P. vernoni, are rainforest dwelling species. Virtually all known species of the subgenus, except the apparently lignicolous P. semiobscura Karavaiev, are ground-nesting (both terrestrial and subterranean) and their nesting habits were discussed in detail by Kohout (1997) and Robson & Kohout (2007). The lithocolous nesting habit of P. thusnelda Forel was reported by Robson & Kohout (2005) and a similar nesting habit inside rock crevices has recently been discovered in P. anderseni (Kohout unpublished).

Species Groups
based on Kohout 2013

The subgenus Hagiomyrma had never been formally subdivided (Emery 1925; Dorow 1995) until Andersen (2000) introduced four species-groups pertinent to his work on the ants of monsoonal Australia. He recognised the ammon-group, schenkii-group, trapezoidea-group and an unnamed ‘Group A’, that he distinguished mostly by the shape of the petiolar dorsum, the comparative length of the petiolar and propodeal spines, the length of the antennal scapes and the colour of the body. Three more species-groups are proposed here, the metella-group, the penelope-group and the tubifera-group, with Andersen’s ‘Group A’ incorporated within the trapezoidea-group. Most of these groups intergrade on morphological grounds and within the groups the species tend to polarise into several complexes.

ammon group
Andersen (2000) included two species, P. ammon and P. angusta, within the ammon-group which is expanded here to incorporate 16 species. It includes most of the larger species of the subgenus (generally HL > 1.90) which have promesonotal lateral margins that are only weakly converging posteriorly (PMI < 160) and generally hairless scapes. The species have uniformly black ground colour which is often obscured by golden or silvery pubscence. The dorsum of the gaster is usually covered with rich, golden pubescence (except in P. semiaurata Mayr) with a rather distinct, very dark, reddish-brown, median patch in the species of the callima-complex, or without a dark patch in the species of the ammon-complex. Most species of the ammon-group have a scale-like petiolar node, however, P. burwelli has a columnar petiole with a widely rounded dorsum. The majority of ammon-group species tend to be stoutly built, but some species closely related to P. ammonoeides Roger and P. angusta Forel (ammonoeides-complex) are more slender and elongate and feature distinctly dilate pronotal humeri and rather long, widely divergent, propodeal spines. Polyrhachis ammonoeides has hairs along the antennal scapes and somewhat more distinct sculpturation, and so is intermediate between the ammon-group and the pilbara-complex of the newly proposed penelope-group (see below).

metella group
Polyrhachis metella has always been a difficult species to place. With its strongly anteriorly converging pronotal margins, rather long and slender propodeal and petiolar spines, very high declivity and flat-topped petiole, it resembles some members of Hedomyrma and can be considered an intermediate between that subgenus and Hagiomyrma. It is clearly unrelated to other species of the trapezoidea-group and is consequently placed into a newly proposed metella-group.

penelope group
Most of the smaller species of the subgenus (HL < 1.90) are incorporated into the newly proposed penelope-group. Besides their smaller size and black body colour, most species have golden or silvery pubescence fairly evenly distributed over the gastral dorsum (except P. electra ) or have virtually no gastral pubescence. Consequently most species lack a median patch on the gastral dorsum as seen in species within the ammon-group. The species of the penelope-group can be divided into three complexes. Species in the pilbara-complex are characterised by bristle-like hairs along the antennal scapes and rather coarsely reticulate-punctate body sculpturation. In contrast, species of theanderseni- and penelope-complexes lack antennal hairs and their body sculpture is distinctly more finely, reticulate-punctate. Also, species in the anderseni-complex have the bases of petiolar spines closely approximate and the dorsum of petiole transversely narrow and medially concave. (Species in the penelope-complex, feature widely divergent petiolar spines and a transversely wide and vitually straight petiolar dorsum.

schenkii group
The schenkii-group, as conceived by Andersen (2000), includes mostly reddish-coloured species with the leading edge of the antennal scapes fringed with short, bristle-like hairs (except in P. bohemia) and relatively coarsely reticulate or vermiculate-punctate body sculpturation. Besides P. schenkii Forel, P. lachesis Forel and P. lydiae Forel, listed by Andersen (2000), the group also includes P. paxilla Fr. Smith and several newly described species. Within the group species tend to polarise into two complexes, centring on either P. schenkii or P. lachesis. Species allied to P. schenkii are smaller (HL <1.90), with strongly posteriorly converging promesonotal margins (PMI ± 200) and finer sculpturation. In contrast, the species more closely related to P. lachesis, are larger (HL ± 2.00), with the promesonotal margins less strongly converging posteriorly (PMI < 185) and with more-or-less distinct, vermiculate-rugose sculpturation.

tubifera group
Polyrhachis tubifera Forel, previously placed in the ammon-group by Andersen (2000), is here included, with P. diversa, in a new tubifera species-group characterised by a distinctly short and broad mesosomal dorsum, propodeal spiracles situated on relatively long, laterally projecting tubercules and very short propodeal and petiolar spines.

trapezoidea group
The trapezoidea-group was proposed by Andersen (2000) to accommodate P. trapezoidea and ‘a few species of Hagiomyrma’ with a ‘dorsally flattened petiolar node’. Besides P. trapezoidea Mayr, only two other species, P. thusnelda Forel and the more distantly related P. metella Fr. Smith, feature a high columnar petiole with a distinctly flat dorsum. Two other species, P. darlingtoni and P. nourlangie, feature a distinctly low and broad petiole with a somewhat flat dorsum and very short petiolar spines. These latter species also agree with Andersen’s (2000) definition of his ‘Group A’, that constituted mostly ‘smaller, more gracile species with very reduced petiolar spines’. Polyrhachis nourlangie is ‘endemic to sandstone escarpments of the northern Top End’ and is undoubtedly the species Andersen was refering to when proposing his new group. Polyrhachis darlingtoni and P. nourlangie are closely related and form a distinct darlingtoni-complex within the trapezoidea-group.

Nomenclature

 *  HAGIOMYRMA [subgenus of Polyrhachis]
 * Hagiomyrma Wheeler, W.M. 1911c: 860 [as subgenus of Polyrhachis]. Type-species: Formica ammon, by original designation.

Description
Kohout (2013)

Worker
Small to moderately large ants (HL 1.30-2.80) with general characteristics of the genus. Anterior clypeal margin usually with distinct, denticulate, median flange (as in P. ammon), simply truncate (as in P. anderseni) or with deep, open, ‘V’-shaped emargination (as in P. metella Fr. Smith). Clypeus with median, longitudinal carina; sinuate or straight in profile. Frontal carinae sinuate with moderately raised margins at midlength; central area relatively wide with more-or-less distinct frontal furrow or weakly raised carina. Dorsum of mesosoma distinctly laterally marginate along its entire length. Pronotal dorsum generally near quadrate with lateral margins subparallel or converging posteriorly (as in P. schenkii Forel, P. trapezoidea Mayr or P. weiri ); more rarely margins anteriorly converging (strongly as in P. metella Fr. Smith or weakly as in P. darlingtoni, P. dougcooki and P. feehani ). Pronotal humeri unarmed with margins weakly to moderately laminate, often dilated, widely or narrowly rounded or more rarely bluntly angular (as in P. schenkii Forel and P. vernoni ). Promesonotal suture distinct; metanotal groove often distinct laterally, but weakly impressed dorsally, or virtually lacking. Propodeum armed with a pair of more-or-less horizontal, subparallel or divergent, acute spines. Petiole scale-like or rarely columnar (as in trapezoidea-group species), armed with a pair of acute spines that can be subparallel or divergent, horizontal or curved downwards (as in P. uncaria ), upwards (as in P. stricta ), or re-curved and hook-like (as in P. ammonoeides Roger); dorsum narrowly rounded or rarely with flat platform that can be horizontal (as in P. thusnelda Forel) or sloping posteriorly (as in P. trapezoidea Mayr, P. darlingtoni and P. nourlangie ).

Queen
Very similar to worker, with usual characters identifying full sexuality, including three ocelli and complete thoracic structure with wings. Besides larger size (except in P. semiaurata Mayr), differing in distinctly larger eyes and distinctly shorter propodeal and petiolar spines. Sculpturation, pilosity, pubescence and colour virtually identical to that in worker.

Male
Males are unknown for most of the species and as such their treatment was not attempted here. However, where known, their presence in collections is indicated under each species.