Here we describe the diversity of the Malagasy Nesomyrmex brevicornis-group as the final installment of series describing the complete Malagasy Nesomyrmex fauna. In the current paper introduce the Nesomyrmex brevicornis-group, a newly outlined species group. We split this group from one of the four former groups, Nesomyrmex madecassus-group (sensu Csősz and Fisher 2015). The relatively small number of individuals available within the Nesomyrmex brevicornis-group relative to the large number of OTUs hampers the use of sophisticated statistical techniques to evaluate the morphological data. Instead, we assess the diversity of the Nesomyrmex brevicornis-group via a conventional morphology-based approach relying upon non-numeric characters (shape, sculpture, color etc.) recorded by simple eye inspection. Morphometric data are used as secondary data to confirm the most probable boundaries between species, but without employing statistical analyses. We rejected prior species hypotheses imposed by the primary approach if a non-overlapping range of a single index calculated from continuous numeric traits was found between two hypothesized species. Our methods render every species in this revisionary work separable via both salient features and morphometric traits. Our approach reveals the existence of nine morphologically distinct species, Nesomyrmex brevicornis sp. n., Nesomyrmex brunneus sp. n., Nesomyrmex cingulatus sp. n., Nesomyrmex edentates sp. n., Nesomyrmex flavigaster sp. n., Nesomyrmex longiceps sp. n., Nesomyrmex minutus sp. n., Nesomyrmex punctaticeps sp. n., and Nesomyrmex sellaris sp. n.. Geographic maps showing the distribution of each species are provided, along with an updated key to workers of Malagasy Nesomyrmex species groups that includes the newly outlined Nesomyrmex brevicornis-group.
Keywords: Madagascar; biogeography; morphometry; species delimitation; taxonomy.