The colonization of a new habitat affords an important advantage to the successful pioneer species because competitors, predators and parasites are likely to be out of step. Here, we report the first retrieval and molecular characterization of a cryo-benthic community of isopod crustaceans that live at depths of 80-150m on the underside of a floating shelf-ice tongue at the Drescher Inlet (Riiser-Larsen Ice Shelf), Eastern Weddell Sea. The specimens were retrieved with a sampler mounted on a remotely operated vehicle (ROV) when video transsects were carried out. The molecular analysis of mitochondrial and nuclear genes of four specimens spanning the size range of individuals collected confirmed that (1) all belonged to a single species and that (2) this species has previously been identified in benthic communities in the Eastern Weddell Sea as Antarcturus cf. spinacoronatus. The molecular phylogeny shows that the cryo-benthic A. cf. spinacoronatus are deeply nested in a family of isopods characterized by increasing complexity of morphological and behavioural adaptations to the acquisition of detrital and planktonic food particles. This demonstrates that the floating shelf-ice was likely colonized from the seafloor and not vice versa and that the filter-feeding life style of A. cf. spinacoronatus formed a predisposition playing a key role in the colonization of the new habitat. Density estimates of A. spinacoronatus under the floating shelf ice (25 adults and 190 juveniles per square meter) are significantly higher than on the seafloor, suggesting that the transition to the new habitat devoid of any macrofaunal competition or predation provides a major advantage to the species and thus may be a geographically more widespread phenomenon.