Seven species of the ctenostome bryozoan genus Alcyonidium from Magellanic, Patagonian and Antarctic shelf coastal waters are described using molecular genetic and morphological characteristics. One species is limited to cold temperate South America. A second species is reported from five stations in the Magellan Strait and a single station in the Palmer Archipelago, Antarctic Peninsula. The remaining five species appear to be endemic to Antarctica; Alcyonidium epispiculum, A. scolecoideum and A. simulatum are species new to science, A. australe, A. eightsi and A. flabelliforme are substantially revised and A. pelagosphaerum is upgraded to species level. Genetic diversity is least in the circumpolar Antarctic species Alcyonidium flabelliforme and greatest in the epibiotic A. eightsi, recorded only from the Palmer Archipelago. The latter is shown to brood lecithotrophic larvae with predicted minimum dispersal capability, five of the remaining species are inferred to shed planktonic larvae with potentially wide dispersal abilities. Reproductive mode of one species is unknown. A phylogenetic analysis of five haplotypes recognized shows the ancestral haplotype to belong to the broadcast spawner A. epispiculum. The two most recently diverged haplotypes were found in the brooding species A. eightsi.