First bipolar benthic brooder

A bipolar distribution is one in which a taxon occurs at high northern and southern latitudes but is absent in the latitudes between. In spite of the large distance between the Arctic and Antarctic, there are records of biota with bipolar distributions, both currently and in the geological past. To date, combined morphological and genetic studies of organisms such as bacteria and foram-inifera have confirmed the occurrence of some species in both polar regions. Bipolar genera and families are also known in larger invertebrates, e.g. in crustaceans and molluscs, and a recent Census of Marine Life report suggested that more than 200 metazoan species may have bipolar distributions. Here we investigated specimens of the the cheilostome bryozoan Callpora weslawski from both Arctic and Antarctic localities. To our knowledge this is the first benthic brooder to be found in both polar regions and is the first record of a species of Callopora in Antarctic waters. We used scanning electron microscopy and statistical analyses to confirm the morphological identity of individuals. The encrusting nature of the species, its distribution in the deep Weddell Sea and its rarity mean that genetic confirmation of bipolarity may take years or decades. Possible paths of distribution are discussed, including the Pangea break-up, Plio-Pleistocene glaciations, isothermal submergence via off-shelf or abyssal currents and anthropogenic transport.

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