Imparipes specus sp. nov., a new scutacarid mite species (Acari, Heterostigmatina: Scutacaridae) associated with the blind cave trapdoor spider Troglodiplura beirutpakbarai Harvey and Rix, 2020 (Araneae, Mygalomorphae: Anamidae)

Species of the mite family Scutacaridae (Acari, Heterostigmatina) are often associated with animals like mammals or arthropods, either as inquilines and/or as phoronts. Among arthropods, reports of scutacarids linked to other arachnids, however, are rare. In this paper, we describe a new species, Imparipes specus sp. nov., which is a phoront of the Australian troglobiotic nemesoid spider Troglodiplura beirutpakbarai (Araneae: Mygalomorpha: Anamidae). This association is noteworthy not only because of the unusual host but also because it represents one of the few records of a scutacarid from a cave environment and the first troglobiotic heterostigmatic mite from Australia. Imparipes specus was found attached to the coxal region of large subadult and adult spiders, and it remains unclear whether it should also be considered an inquiline or solely a phoront. Morphometric comparisons of I. specus specimens from two different caves revealed only very subtle differences. Muscle strands of the idiosomal region and the legs were clearly visible in microscopic slides of I. specus, which could point to unusually strong muscle fibers, or may reflect an interaction between preservation state and embedding medium.