Recently the ant genus Paratrechina (broad sense) was found to be paraphyletic, with all but one species being transferred to the revived genera Nylanderia and Paraparatrechina (LaPolla et al. 2010a; LaPolla et al. 2010c; LaPolla et al. 2011a). The sole remaining species within Paratrechina was Paratrechina longicornis (see LaPolla et al. 2010b). The discovery of Paratrechina (broad sense) paraphyly was not particularly surprising, because Paratrechina longicornis possesses a morphology that had long been noted as being different from other members of the genus with especially elongated scapes, head and tibiae, coupled with a distinctly shaped mesosoma and unusual mesosomal setal pattern (Trager 1984; LaPolla et al. 2010a).

One particularly interesting and important aspect of Paratrechina longicornis biology is that it is perhaps the most widespread ant species in the world (Wetterer 2008), owing to the ease with which it is spread by human activities and the ability to survive even in extremely anthropogenically changed environments. This species has literally been spread around the planet, being found in almost every urban center in the tropics; it can also widely be found in greenhouses and other manmade structures in cool temperate climates (Wetterer 2008). Where exactly the species is native has been a source of debate and uncertainty, although the evidence seems to suggest it is native to Southeast Asia (Wetterer 2008; LaPolla et al. 2010a).

The unusual morphology of Paratrechina longicornis, coupled with its widespread tramp status, makes the discovery of a new species within the genus particularly important. Here we report on such a discovery from Africa (records from Angola, Mozambique and Tanzania). The discovery of this new species of Paratrechina now requires a reevaluation of the previous morphological definition of the genus (LaPolla et al. 2010a) and may contribute to our understanding of the native range of Paratrechina longicornis.

The worker of Paratrechina zanjensis can easily be separated from Paratrechina longicornis based on the presence of erect macrosetae on the scapes. There are several other notable differences between the two species (see Figs 1–6). The propodeal dorsal face of Paratrechina zanjensis is more convex than is observed in Paratrechina longicornis. Similarly, the pronotum and to a lesser degree the mesonotum are more convex in Paratrechina zanjensis, being almost flat in Paratrechina longicornis. The metanotal area is also longer and more distinct in Paratrechina zanjensis, being more strongly separated from the mesonotum and propodeum. Paratrechina zanjensis has erect macrosetae that are dark rather than pale as in Paratrechina longicornis, the body is glossier, and largely lacks the opalescent sheen / iridescence that is characteristic of Paratrechina longicornis. Unfortunately, the male and queen for Paratrechina zanjensis remain unknown. Paratrechina zanjensis is superficially similar to Nylanderia silvula (see images in LaPolla et al. 2011b), but can readily be distinguished from this species by its mandibular dentition (5 teeth in Paratrechina, 6 in Nylanderia), larger eyes, longer limbs and less strongly domed propodeum.

Paratrechina has been shown to be a distinct lineage within the Prenolepis genus-group (LaPolla et al. 2010a), but with the discovery of Paratrechina zanjensis, some modifications need to be made to the genus diagnosis. The biggest change comes from the fact that Paratrechina zanjensis possesses erect macrosetae on their scapes, so the lack of erect macrosetae is no longer diagnostic for the genus. This is not particularly surprising; for instance, even though most Nylanderia species possess erect macrosetae on the scapes, a few species do not (Kallal and LaPolla 2012). This trait is also variable within Zatania as well, although the erect macrosetae when present in this genus are short (LaPolla et al. 2012), and despite the fact that nearly every species of Paraparatrechina lacks erect macrosetae on the scape, at least one species (Paraparatrechina bufona) possesses them (LaPolla et al. 2010c). With a scape index above 180, and with most specimens registering above 200, Paratrechina possess among the longest scapes relative to head width within the genus-group (Fig. 10). The same can be said for their eye length relative to their head width (Fig. 11). Only species within the genera Prenolepis and Zatania seem to have such long scapes and eyes relative to their head width (Figs 10, 11).

The similarity of the scapes of Paratrechina, Prenolepis and Zatania extends to other aspects of overall worker morphology within these genera, and these three genera are the most likely members of the Prenolepis genus-group to be confused with each other. This is because workers from these genera generally possess elongated heads, scapes, mesosomata, and legs. Whether or not the elongated state of these morphological features represents the plesiomorphic state (as might be suggested by the basally diverging position of Prenolepis within the clade, see LaPolla et al. 2010a and LaPolla et al. 2012) within the genus-group or has been independently derived several times is unclear. There are diagnostic features, however, that separate workers in these genera. Paratrechina can be separated from Prenolepis by the fact that Paratrechina lack a constriction immediately behind the pronotum. From Zatania, where a constriction behind the pronotum is variable, the number of mandibular teeth is an important diagnostic character. When a constriction is not present in a Zatania species those species also possess 6 teeth versus the 5 teeth found in Paratrechina.

As was found in Zatania (LaPolla et al. 2012), the male morphology of Paratrechina does provide some important features that show it to be a distinct lineage based on morphological characters. In both Prenolepis and Zatania the parameres for instance are thin and elongated. While the male is only known for Paratrechina longicornis, in that species the parameres are unique and quite different from either Prenolepis or Zatania. In Paratrechina longicornis the male parameres are shorter and more robust (Figs 14, 16), with a more overall dorsal orientation, and the parameres are curved. This is a unique conformation observed among Prenolepis genus-group species to date, but exploration of male genitalic diversity among Pseudolasius, a close relative of Paratrechina, would be warranted. Among Euprenolepis, the putative sister group of Paratrechina (LaPolla et al. 2010a), the parameres of some species such as Euprenolepis procera and Euprenolepis wittei also curve entad (LaPolla 2009), but they are not as extended dorsally as in Paratrechina longicornis (Fig. 14).

Paratrechina zanjensis is certainly native to Africa, to date only being found in natural or minimally disturbed habitats. The presence of a new species of Paratrechina in Africa is interesting because Paratrechina longicornis is thought to be native to Asia (although some authors have considered it native to Africa, see Wetterer 2008 for review). Wetterer (2008) argued that Paratrechina longicornis is native to Southeast Asia, because it is only in this region, despite the extremely wide distribution of the species globally, that Paratrechina longicornis is found in native, undisturbed habitats. LaPolla et al. (2010a) also argued for a Southeast Asian origin of the genus (then thought to be monotypic) based on the fact that Paratrechina was found within a clade of largely Southeast Asian species (Euprenolepis and Pseudolasius; a few species of Pseudolasius are known outside of SE Asia extending into Australia). Regardless, the presence of another Paratrechina species in Africa is potentially important to interpreting the biogeography of Paratrechina longicornis. Certainly it is not unusual to have ant genera that span Africa and Asia, and this appears to be another example of an Afro-Asian genus. Since we know that Paratrechina is not monotypic the question becomes, are there additional new species awaiting discovery within the genus? There have been two monographic revisions of Prenolepis genus-group genera within Africa: Nylanderia (LaPolla et al. 2011b) and Paraparatrechina (LaPolla et al. 2010c). These studies did not find evidence of additional Paratrechina species, despite the fact these two studies examined thousands of Prenolepis genus-group specimens from the across the continent. Southeast Asia may very well be the place to look for new Paratrechina species because, other than Euprenolepis (LaPolla 2009), the other genera within the Prenolepis genus-group remain unrevised within the region.