A revision of the ant genus Mystrium in the Malagasy region with description of six new species and remarks on Amblyopone and Stigmatomma (Hymenoptera, Formicidae, Amblyoponinae)

The genus Mystrium is revised for the Malagasy region. Six species, Mystrium barrybressleri sp. n., M. labyrinth sp. n., M. eques sp. n., M. mirror sp. n., M. shadow sp. n., and M. janovitzi sp. n. are described as new. Two existing names, Mystrium fallax Forel and M. stadelmanni Forel, are synonymized with M. voeltzkowi Forel and M. mysticum Roger, respectively. All recognized species, including species outside of the Malagasy region, are assigned to one of the three newly proposed species groups. The associations between existing names and males are reexamined, and males of eight of the ten Malagasy species are described or redescribed. The taxonomic history of Mystrium highlights the importance of using unique identifiers when designating type specimens and the use of deposited vouchers in phylogenetic and ecological studies. Keys to species for workers, queens, and males are provided. Furthermore, a neotype for M. mysticum is designated, as well as lectotypes for M. camillae Emery, M. rogeri Forel, M. fallax Forel, M. oberthueri Forel, M. stadelmanni Forel, and M. voeltzkowi Forel. Stigmatomma gingivale (Brown) is reassigned to Amblyopone as comb. rev. and Amblyopone awa Xu & Chu, A. kangba Xu & Chu, A. meiliana Xu & Chu, and A. zomae Xu & Chu are transferred to the genus Stigmatomma as comb. n.