Biogeographical mechanisms explaining the distribution of southern temperate taxa have been debated since the XIX century but a consensus has been growing on the combined significance of vicariance and long-distance. In this study we present multi-locus phylogenetic and population-based analyses of high-latitude direct developing Siphonaria species. We include subantarctic Siphonaria populations from several subantarctic provinces (South America, Falkland/Malvinas Islands, South Georgia, the Kerguelen and Macquarie islands). Through molecular reconstructions we present a clear picture about 1) the evolutionary relationships within subantarctic Siphonaria 2) the number of valid taxonomic units and 3) the geographic distribution of each taxon. With this information it was possible to unveil the biogeography of the genus across the Southern Ocean. Phylogenetic reconstructions highlight the existence of two clearly discriminated and broadly distributed subantarctic lineages of Siphonaria identified as S. lateralis and S. fuegiensis. These cryptic and sympatric Siphonaria species were formerly recognized as Kerguelenella lateralis but their phylogenetic positions indicate that they are included in the genus Siphonaria. Divergence-time estimates suggest that the separation between S. lateralis and S. fuegiensis occurred ? 4.0 million years ago (Ma) (between 3.0 – 8.0 Ma). After this cladogenetic process they followed different evolutionary pathways even when they are currently sympatric across Subantarctica. Extremely low levels of genetic diversity characterize subantarctic Siphonaria species reflecting the role of Quaternary glacial cycles in their respective demographic histories. The presence of dominant and broadly distributed haplotypes in both species suggests high levels of connectivity among geographically distant localities. Both, S. lateralis and S. fuegiensis, constitute sister cryptic species broadly distributed in Subantarctica, from southern South America to Macquarie islands. Transoceanic similarities, similar phylogeographic signals and very low levels of genetic diversity recorded in these direct-developing species reveal the prevalence of long-distance dispersal, probably mediated by rafting in circumpolar currents. We propose a biogeographic model for the Quaternary to explain the broad distributions of these higher latitude pulmonates, their presence on isolated subantarctic islands and their low genetic diversity and simple structure over thousands of kilometers.