Polyrhachis breviorspinosa

Polyrhachis breviorspinosa appears to be a rather uncommon species, endemic to the islands along the north-western coast of New Guinea. Besides the specimens of the original series from Liki Island, the only other comparable specimens seen were collected on Biak Island (Biak I., beach area, 17.vii.1957, D. Elmo Hardy; Biak I., 22-30.vi.1962, J.L. Gressitt – all ) (Kohout, 2012).

Identification
Donisthorpe (1947) described P. relucens breviorspinosa in one short sentence by stating that it 'Differs from the typical form in having shorter spines to the pronotum and the petiole'. During a visit to the CASC, Kohout (2012) examined the syntypes and additional specimens from the original series (E.S. Ross coll.) and compared them with a type compared voucher specimen of Polyrhachis relucens (Latreille). The two taxa are rather dissimilar and he is confident they represent separate species. Polyrhachis breviorspinosa is clearly distinguished by its more gracile stature, markedly slender pronotal spines and propodeum, which lacks a distinct border between the dorsum and declivity. In contrast, P. relucens has a distinctly broader body, notably across the mesosoma, broadly based pronotal spines and a propodeal dorsum that is clearly separated from the declivity breviorspinosa is armed with distinctly short and slender spines and the dorsum between them is relatively narrow, weakly concave and without an intercalary spine or tooth. In contrast, the petiolar spines in P. relucens are relatively thick and the petiolar dorsum furnished with a distinct intercalary tooth. Polyrhachis breviorspinosa is more similar to Polyrhachis litigiosa Emery from New Guinea; both are slender in stature and have a uniformly black body and appendages. However, P. breviorspinosa has a distinctly less transverse mesonotal dorsum, shorter petiolar spines and markedly less abundant erect pilosity that is much diluted on the mesosomal dorsum and the gaster, and is completely missing from the antennal scapes and petiole. In contrast, the mesonotal dorsum in P. litigiosa is distinctly wider, the petiolar spines longer, the dorsum of the petiole has a minute intercalary tooth or distinct tubercula and erect to semierect, medium length hairs are abundant over most of the body surfaces, with a fringe of short hairs lining the leading edges of the antennal scapes. (Modified from Kohout, 2012.)

Distribution based on Regional Taxon Lists
Indo-Australian Region: Papua New Guinea.

Nomenclature

 *  breviorspinosa. Polyrhachis (Myrma) relucens var. breviorspinosa Donisthorpe, 1947d: 194 (w.) NEW GUINEA. Raised to species: Kohout, 2012: 27.

Syntype workers from Liki I., Maffin Bay, New Guinea, viii.1944 (E.S. Ross) (examined by Kohout, 2012).

Additional References

 * Kohout, R.J. 2012. A review of the Australian Polyrhachis ants of the subgenera Myrma Billberg, Myrmatopa Forel, Myrmothrinax Forel and Polyrhachis Fr. Smith (Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum – Nature 56(1): 25-59.