Benthic marine habitats in Canada have been well-sampled since the annual groundfish survey commenced in 1970. However, trawl surveys cover only non-rocky sediments and many species collected are not identified to lower taxa, leaving large gaps in our understanding of benthic diversity. Sponges are a prime example. Sponges preferentially attach to hard substrates and therefore trawls do not sample the most sponge-rich habitats. Furthermore, the identification of sponge species requires

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... comparative taxonomy that cannot be performed on board a survey vessel. While almost 9000 sponge species are known globally, in Canadian trawl surveys only few characteristic species are identified, otherwise sponge catches are frequently narrowed only to the phylum level. Sponges provide important habitat for fish and other animals and as such play a valuable role in overall marine ecosystem functioning. Targeted sampling of sponges was carried out using a remotely operated vehicle (ROV), box cores and short Agassiz trawl tows. Skeleton morphology and DNA barcoding were used to develop a new view of sponge community structure and habitat types in the eastern Canadian Arctic and Subarctic. This work covers a wide geographic area from the North Labrador Sea to Northern Baffin Bay. Sponges were also collected and described for the first time from Frobisher Bay. In total, 61 distinct sponge species were identified, six of which were described as geographic range extensions, with one considered a potential species new to science. These results substantially increase the number of marine sponges known from eastern Canada. Many of these sponges are small, cryptic, or encrusting species that would be ignored in non-targeted sampling. This work is presented as a field guide of sponge species found in the study region in order to provide a baseline for future benthic work in the Arctic and this increased knowledge of the biodiversity of the region will help future conservation efforts in Canada. In view of the increased iii anthropogenic influences anticipated for Arctic regions, further understanding of benthic biodiversity and ecosystem functioning is critical. iv