The Lepetidae are currently assumed to be represented by only one valid species in the Magellan region: Iothia emarginuloides (Philippi, 1868), of which Tectura (Pilidium) coppingeri Smith, 1881, and Iothia coppingeri magellanica Linse, 2002, were regarded as synonyms. The extant records of this species are scarce, although they suggest a wide distributional range in the Pacific Ocean, from off Concepción (36°S) to the Beagle Channel (55°S), and a restricted distribution in the Atlantic Ocean, where the species is only known from the Malvinas / Falkland Islands and Isla de los Estados (about 54.5°S). This study provides new information on the occurrence of the genus Iothia in the Magellan region, including morphological, anatomical and molecular evidence. The synonymy of Tectura (Pilidium) coppingeri, Iothia coppingeri magellanica and Iothia emarginuloides is ratified. The species is properly redescribed and figured, and its intraspecific variability discussed, particularly regarding its relation with depths. Furthermore, the distribution of this species in the southwestern Atlantic is extended north to San Matías Gulf (about 41°S). Iothia megalodon Warén, Nakano & Sellanes, 2011, previously known from deep waters off Concepción (36°S), is here reported for the first time for the Magellan region. Its finding in shallow waters from the Beagle Channel greatly extends its distribution both latitudinally and bathymetrically.