Unrecognized Ant Megadiversity in the Australian Monsoonal Tropics: The <i>Melophorus castaneus</i> Heterick, Castalanelli &amp; Shattuck Species Group (Hymenoptera: Formicidae)

ABSTRACT This paper continues the documentation of remarkable levels of undescribed ant diversity in the Australian monsoonal (seasonal) tropics. It considers the Melophorus castaneus Heterick, Castalanelli &amp; Shattuck species group, as considered here consisting of four described species: M. castaneus , M. clypeatus Heterick, Castalanelli &amp; Shattuck, M. kuklos Heterick, Castalanelli &amp; Shattuck, and M. teretinotus Heterick, Castalanelli &amp; Shattuck. Based on an integration of morphological, genetic (CO1), and distributional information, we recognize 24 species among 79 sequenced specimens from the group in monsoonal Australia, only one of which ( M. teretinotus ) is described. Our species delimitations are strongly supported by species inference from the Poisson tree processes model. We provide images of all our recognized species, along with images of four additional monsoonal species from the group that were not sequenced. Of the 28 monsoonal species in total that we document, 20 occur in the Top End of the Northern Territory, and none of these are known from elsewhere. Most locations within the Top End remain unsampled, and so many more species can therefore be expected to occur in it, and much more so elsewhere in monsoonal Australia. The total number of monsoonal species within the M. castaneus group is therefore very likely well over 50, only one of which is described. Our findings provide further evidence that the ant fauna of monsoonal Australia numbers several thousand species, a number far higher than estimated for any other of the world's regional ant faunas.