Rugowithius longissimus is a species of pseudoscorpion in the Withiidae family. It was described in 2015 by Australian arachnologist Mark Harvey. The specific epithet longissimus (Latin: 'longest') refers to the large size of the species compared to Rugowithius bulbosus.
Body lengths of males are 2.50âÂÂ2.85 mm; that of the female paratype is 2.24 mm. The colour is dark red-brown.
The species occurs in Far North Queensland in rainforest habitats. The type locality is 20 km north of Cape Tribulation.
The pseudoscorpions are terrestrial predators.