Polyrhachis continua species-group

The species in this group are members of the subgenus Myrma.

Identification

Distribution

The continua-group comprises mostly Melanesian elements with its known distribution extending from Sulawesi and the Moluccas (Ternate I.), across New Guinea to the Bismarck Archipelago, including New Britain, New Ireland and Manus Island, and south to Cape York Peninsula in Queensland. However, the group is predominantly New Guinean, where it is most diverse, both in the number of species and morphologically.

Biology

Generally, species of the continua-group are uncommonly encountered in the field and consequently they are relatively poorly represented in most of the collections examined. Members of the continua-group are lignicolous, using various tree cavities, including rotten logs or hollow internodes of dry bamboo stems for their nesting sites. Only one species (Polyrhachis tapini) was recorded nesting in soil in the ground (Taylor, specimen label data). As continua-group species are lignicolous they are often overlooked, or missed by the more common mass-collecting methods such as insecticidal fogging or pitfall traps. Also, their colonies appear to be relatively small, mostly well under 50 individuals, which means that only a small number of workers will be foraging at any one time. This may explain why one of the described species is known only from the original series (Polyrhachis conops) and three of the newly described species (Polyrhachis gazelle, Polyrhachis planoculata and Polyrhachis sinuata) are each known only from a single specimen.

Diagnosis

Worker

Medium-sized to relatively large ants (HL > 2.30) with general characteristics of the genus and subgenus. Head with sides in front of eyes subparallel or weakly convex towards mandibular bases; sides in most species distinctly wider behind the eyes with postocular and lateral ridges extending on each side towards occipital corners. Eyes usually large, situated well back, giving face a characteristic elongated appearance; in some species eyes distinctly posteriorly protracted (e.g. Polyrhachis conops), or posteriorly truncate (Polyrhachis sinuata); however, in one species (Polyrhachis planoculata) eyes virtually flat, not reaching cephalic outline in full face view. Antennal scapes relatively long (SL >180). Mesosoma in profile with evenly convex outline, in most species without distinct border between propodeal dorsum and declivity. Sculpture of head and mesosoma ranging from rather finely and uniformly reticulate-punctate (as in Polyrhachis inusitata and Polyrhachis tapini), to distinctly longitudinally striate (as in Polyrhachis conops and Polyrhachis manusensis), with gaster finely shagreened. Appressed pubescence virtually lacking from most parts of body in all species, except for a very fine, diluted, reddish-brown patch on gastral dorsum. Dorsal surfaces of mesosoma and petiole almost completely hairless (as in Polyrhachis continua), or with rather short, erect hairs (as in Polyrhachis spinifera or Polyrhachis manusensis); head and apex of gaster in most species with several short or medium length, erect or posteriorly inclined, hairs. Colour of all species is virtually black throughout with somewhat semiopaque shine; appendages black or dark reddish brown.

Queen

Apart from distinctly larger size and usual sexual characters, including three ocelli and fully developed mesosoma with wings, very similar to worker.

Male

Males of only a few species are known and as such, their treatment has not been attempted here.

Species Complexes

Within the group the species clearly polarise into two complexes, centring on P. continua and P. conops.

Polyrhachis continua complex

Includes species with the petiole distinctly higher than wide and armed with rather elongated dorsal spines and usually very short or rudimentary lateral teeth. Distributed throughout mainland New Guinea, extending westwards to Indonesia and southwards to Cape York Peninsula in Queensland,

Polyrhachis conops complex

Includes species characterised by a petiolar node that is only marginally higher than wide and armed with short dorsal spines that are barely longer than their basal width and well developed and acute lateral teeth (except in P. gazelle). Species in this complex appear to be limited to the islands of the Bismarck Archipelago.

Related Pages

Polyrhachis
subgenus Myrma

References

Kohout, R.J. 2013. A review of the Polyrhachis continua species-group of the subgenus Myrma Billberg (Hymenoptera: Formicidae: Formicinae) with keys and descriptions of new species. Australian Entomologist 40(1), 13-46.