Listrura tetraradiata, new species, is described from a small headwater stream of the Lagoa de Araruama system, a coastal lagoon system in Rio de Janeiro state, southeastern Brazil. It is easily distinguished from other species of the genus by having four pectoral fin rays (vs three in Listrura camposi and one in Listrura nematopteryx) and branched rays in pectoral, dorsal and anal fins, these character states unique among glanapterygines. It also differs from its congeners by higher number of premaxillary and dentary teeth and fewer number of procurrent caudal fin rays.