More diverse than expected: distributional patterns of Oecidiobranchus Hessler, 1970 (Isopoda, Asellota) on the Greenland-Iceland-Faeroe Ridge based on molecular markers

Oecidiobranchus (Isopoda, Asellota) is distinctive among asellote isopod genera in that most of its known species occur in the Nordic Seas and the Arctic Ocean. Some of these species are known only from a few specimens (i.e., poorly known). We used a combined morphological and genetic approach to evaluate the diversity of Oecidiobranchus species in this region. On the basis of genetics, at least three species were recognized, representing Oecidiobranchus cf. nanseni, Oecidiobranchus cf. plebejum, and a third, probably undescribed species. Oecidiobranchus cf. plebejum was found at several locations to the north of the large Greenland-Iceland-Faeroe Ridge, while O. cf. nanseni occurred on both sides of the ridge; temporal or spatial changes during and after the last ice age may have contributed to the genetic differences of populations on each side of the ridge. The wide distribution of the genus in the Nordic Seas and the Arctic Ocean suggests that the genus has been present there for an extensive period.