An unexpected Australian piece of the palm bug puzzle (Heteroptera: Thaumastocoridae: Xylastodorinae): natural history, comparative morphology and systematics

Palm bugs are an elusive group of true bugs, replete with conundrums, such as living fossils, transoceanic disjunctions, rarity, palm associations, and autapomorphic morphology. Knowledge of the group is historically slim, up until the recent documentation of a flux of new species in both the south-west Pacific and the Neotropical region. In this work we present a systematic treatment of the first palm bug from continental Australia, restricted to the wet tropics of Queensland. This taxon, Austrodiscocoris monteithi gen. nov., sp. nov., is described, as is its specialist association with the widespread Alexandra palm species, Archontophoenix alexandrae. This new palm bug species shares characters with both south-west Pacific xylastodorines as well as species of the Western Hemisphere genus Discocoris. To determine its systematic position we report on fine scale morphological observations, using optical and scanning electron microscopy, as well as X-ray microtomography (micro-CT), with the latter employed for the first time to disclose the internal anatomy of the reproductive systems of both sexes. This information is incorporated in an extended morphological-based phylogenetic analysis of the subfamily Xylastodorinae, for two data partitions: (1) complete taxon partition: all Recent plus fossil taxa (n = 39) and (2) trimmed taxon partition: recent taxa with sufficient data coverage (n = 29). The results verify a highly supported Thaumastocoridae and the two included subfamilies. Austrodiscocoris monteithi is imbedded in a clade that includes the Neotropical genera Discocoris and Xylastotylus. Separately, the Norfolk Island species Latebracoris norfolcensis is in a well-supported clade that includes the Neotropical genus Neolatebracoris and the Oriental genus Thaicoris. The work provides a rediagnosis of the subfamily and an identification key to all xylastodorine genera, fossil and extant. It concludes with a discussion on further puzzles on palm bug-palm associations, biogeographic implications, and the value of micro-CT in the search for new character systems in the suborder Heteroptera. ZooBank: urn:lsid:zoobank.org:pub:4378DE99-72BA-4D88-BA5E-4F17A7B77AB8.