Platyarthrus monastirensis sp. n. is a newly described species. Its geographical distribution is limited to Tunisia's central and south-eastern coast, in semi-arid to arid bioclimatic regions. This species is easily distinguishable by its prominent ridges throughout its dorsal surface (cephalon, pereon, and pleon) and the cephalon, with protruding semi-circular median lobe and developed lateral lobes. Platyarthrus monastirensis sp. n. has myrmecophilous habits, and it was collected in ant-nests of seven species.