Synsphyronus leo is a species of pseudoscorpion in the Garypidae family. It is endemic to Australia. It was described in 1987 by Australian arachnologist Mark Harvey. The specific epithet leo (Latin: 'lion') refers both to the type locality and the relatively large size of the species.[1]
Body lengths are 5.2–5.8 mm. Colouration is light yellowish-brown.
The species occurs in south-west Western Australia. The type locality is Lion Island, near Esperance in the Recherche Archipelago, where the pseudoscorpions were found beneath granite slabs.[1]
The pseudoscorpions are terrestrial predators.[1]