Lagynochthonius australicus is a species of pseudoscorpion in the Chthoniidae family. It is endemic to Australia. It was described in 1966 by Austrian arachnologist Max Beier.
The species occurs in south-west Western Australia, where it inhabits plant litter in tall forest habitats. The type locality is Denmark, some 420 km south-south-east of Perth.
The arachnids are terrestrial predators.