Aulacomyrma

Kohout (2007) revised the subgenus and summed up our meager understanding of the biology and natural history of its constituent species: Little is known about their biology and nesting habits, however, a small colony of Polyrhachis dohrni was collected by the author from a dry hollow twig on a living tree at the edge of lowland rainforest. The internal walls of the twig cavity were lined with a little silk. The only other record of a nest is of Polyrhachis wardi, collected by Dr Phil Ward, also from a dry twig of a rainforest tree. The colonies of both species were rather small, with only a few workers (5 and 11 respectively, including 2 and 3 alate queens and a single male). If such a nesting pattern is the norm for other species of the subgenus, that might explain the general scarcity of Aulacomyrma material even in the best collections. This might also account for the fact that all previously described species were based on unique specimens. In spite of the exemplary cooperation of the listed institutions, this situation has only marginally improved in this revision with almost half the new species described from single specimens.

Distribution
The known distribution of the subgenus ranges from the islands of eastern Indonesia (Aru, Misool), across the New Guinean mainland and adjacent islands (Umboi) to the Bismarck Archipelago, including New Britain and New Ireland.

Castes
Males are only known for one species in the subgenus (Polyrhachis wardi).

Nomenclature

 *  AULACOMYRMA [subgenus of Polyrhachis]
 * Aulacomyrma Emery, 1921e: 17 [as subgenus of Polyrhachis]. Type-species: Polyrhachis porcata, by original designation.
 * Aulacomyrma senior synonym of Johnia: Hung, 1967b: 402.
 *  AULACOPONE [Heteroponerinae]
 * Aulacopone Arnol'di, 1930a: 139. Type-species: Aulacopone relicta, by monotypy.
 * [Aulacopone also described as new by Arnol'di, 1930d: 159.]
 * JOHNIA [junior synonym of Aulacomyrma]
 * Johnia Karavaiev, 1927e: 43 [as subgenus of Polyrhachis]. Type-species: Polyrhachis (Johnia) schizospina, by monotypy.
 * Johnia junior synonym of Aulacomyrma: Hung, 1967b: 402.
 * Johnia junior synonym of Aulacomyrma: Hung, 1967b: 402.

Kohout (2007):

Worker
Small ants (HL 1.00-1.70) with general characteristics of the genus. Anterior clypeal margin arcuate, majority of species with small notch or shallow emargination medially. Frontal carinae sinuate with laminate lobes; frontal triangle usually indistinct or visible only in certain illuminations and views. Eyes ranging from flattened to strongly protuberant. Preoccipital margin with a distinct ridge posteriorly and laterally in all but one species (decora), where it is suppressed by overlying cephalic sculpture. Mesosoma with dorsum showing all stages from fully marginate to completely immarginate. Pronotal humeri armed with spines, teeth or simply angular. Promesonotal suture present. Mesonotal and propodeal dorsa virtually fused. Metanotal groove completely lacking or only very weakly indicated by a hairline break in dorsal sculpture and/or by shallow incisions of lateral margins in species with marginate mesosoma. Propodeum terminating posteriorly in a pair of short teeth, tubercles or simply rounded, except in one species (wilsoni), where it is armed with long, mostly outwardly directed spines. Petiole scale-like; dorsal margin acute, usually entire, but occasionally with intercalary teeth or short spines, medially emarginate or unevenly jagged, laterally armed with short spines or teeth. In several species (decora and its allies) petiole deeply transversely sculptured with dorsal margin more-or-less blunt. Base of first gastral segment usually concave medially, accomodating posterior face of petiole; dorsal margin of concavity acute or blunt and often raised above dorsum of segment; first gastral segment sometimes truncate or simply convex. Sculpture of head and body mostly consisting of regularly spaced striae that are either longitudinal or convoluted producing a characteristic “geometrical” appearance; gastral sculpture more modest, usually consisting of longitudinal striae; most distinct on sides of first gastral segment.

Queen
Very much like worker with usual characters identifying full sexuality, including three ocelli and complete thoracic structure with wings. Armament of pronotal humeri somewhat reduced, lateral petiolar spines distinctly shorter. Sculpture of head and body similar to that of worker, pattern of striation following structural characteristics of fully developed mesosoma.

Species Groups
The thirty-six species of Aulacomyrma can be divided, on the basis of external morphological characters, into two, mostly intergrading, species-groups:
 * Polyrhachis porcata species-group
 * Polyrhachis dohrni species-group

The margination of the mesosoma or its partial or complete loss is an important character, evident in a number of species that are intermediate between the dohrni-group, which includes species with a laterally marginate mesosomal dorsum and the porcata-group with a partly or completely immarginate condition. The transition is illustrated by the following series of species: exarata → planata →sculpta → excellens → porcata → orokana →geometrica →decora. In the first species, exarata, a member of the dohrni-group, the mesosoma is fully laterally and posteriorly, marginate. The second species, planata, still has complete lateral margins, but the posterior propodeal margins extend only partly towards the midline as short ridges. They fail to meet medially and there is a gap through which the dorsum meets the declivity. In sculpta, which could be considered intermediate between the dohrni- and porcata-group, the lateral margins of the mesosoma are less distinct posteriorly, leaving the propodeum only weakly marginate laterally and completely immarginate posteriorly. The margins of the mesosoma are incomplete in excellens and related species, with the pronotal margins weak and extending from the pronotal spines for only part of the length of the pronotum. The margins merge with the outermost dorsal striae and curve onto the sides of pronotum, failing to reach the promesonotal suture. The mesonotal-propodeal dorsum is usually only partly marginate, leaving one or the other laterally immarginate. In porcata there is only an indication of weak lateral margins of the mesosoma, with the propodeum terminating in barely distinct tubercles. The propodeum in orokana has a distinct transverse posterior margin, but the lateral margins of mesosoma are completely lost. A complex of species, represented in the series by geometrica, has the mesosoma virtually immarginate, although in some the outermost striae of the mesonotal dorsum form ill-defined lateral margins. Finally decora and its allies have the mesosoma completely immarginate.

Within the series, changes in other characters are also evident, notably in the convexity of the mesosomal dorsum and the degree of concavity of the anterior face of the first gastral segment. In species related to dohrni and excellens, the mesosomal dorsum between the lateral margins is almost flat or only moderately transversely convex, and the first gastral segment is more-or-less distinctly concave anteriorly. By contrast, in species related to porcata and geometrica, the dorsum of mesosoma is distinctly transversely convex and rounds onto the sides in an uninterrupted curve. Also, as the series progresses, the first gastral segment tends to be somewhat less concave and finally culminates in species having the anterior face only truncate or even convex, as in decora. In most species the surface of the petiole is shagreened with the dorsal margin distinctly acute and armed with rather well developed lateral spines. In species allied to decora, the petiolar node in lateral view is blunt with both faces deeply transversely striate and armed with rather short lateral teeth. The affinities of these species are not immediately apparent, but porcata and snellingi, both possessing a transversely striate petiole with a rather acute dorsal margin, evidently represent intermediate forms.

Parallel to the characters discussed above is a change in the form of the sculpture of the mesosoma which, in dohrni-group species, consists mostly of simple, longitudinal striation. The sculpture tends to become more complicated as the series progresses, with the dorsal striation in porcata-group species curved into simple V- or U-shapes, notably on the pronotal dorsum. The sculpture of species at the end of the series is even more complex, featuring variously curved patterns, giving them a characteristic “geometrical” appearance.