Micromegistus thorpei sp. nov. is described from the large carabid beetle Trichosternus fax from the wet tropics of Queensland. This species represents the first Parantennulidae described from Australia, even though the genus was known for more than 50 years, with Australian collections later assumed to be conspecific with the New Zealand species Micromegistus gourlayi Womersley, 1958. Using citizen science records from iNaturalist and collections at the Queensland Museum, I show that Micromegistus occurs in Australia from Melbourne to northern Queensland, and in New Zealand is widely distributed on both islands. In both countries, host beetles include various genera of large carabid beetles, as well as one record from a tenebrionid beetle. Collections from pinned specimens of Queensland carabid beetles suggest the genus is far more diverse than previously thought, and also that they can occupy the subelytral space of their host.