The deep-water sponge fauna of the Canadian Arctic remains to be fully described, particularly in areas that are not sampled by fisheries stock-assessment trawl surveys such as the major bays and fjords of the northern Labrador Sea and Baffin Bay. Frobisher Bay is a large inlet located on the southeast of Baffin Island. We used a remotely operated vehicle, as well as box cores and Agassiz trawls to study the sponge fauna of this bay. Over three years, from 2015 to 2017, sponge specimens were collected representing 24 distinct sponge taxa. Dense gardens of Iophon koltuni Morozov, Sabirov, & Zimina, 2019 were discovered at a site near Hill Island in inner Frobisher Bay. The species has a unique finger-like growth form and provides complex habitat in the inner bay. Other sponge species are new to the Northern Labrador marine ecoregion. In particular, we report geographic range extensions of Tetilla sibirica (Fristedt, 1887) and Craniella polyura (Schmidt, 1870), and provide spicule measurements and descriptions of Iophon piceum (Vosmaer, 1882) and Mycale lingua (Bowerbank, 1866). These species identifications, geographic range extensions, and an expanded description of a species synonym represent the first inventory of the sponge fauna of Frobisher Bay.

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Haliclona (Flagellia) Van Soest, 2017 is a recently erected subgenus characterized by the presence of flagellosigma microscleres which are often distinctive between species (Van Soest 2017). Members of the taxon also have normal sigmas within a confused skeleton formed by oxea megascleres. The subgenus has a global distribution and contains 10 species (Van Soest et al. 2019). A large and abundant new species collected throughout the southern Gulf of St. Lawrence is characterized by thick and abnormally shaped flagellosigmas, two sizes of oxea, and abundant normal sigmas. Lambe (1896) previously reported Haliclona (Flagellia) porosa (Fristedt, 1887) from the Gulf of St. Lawrence, and the species is known to occur in nearby Arctic waters (Fristedt 1887; Lundbeck 1902; Hentschel 1916; Koltun 1959, 1966; Van Soest 2017; Dinn & Leys 2018). However, H. (F.) porosa is characterized by the presence of very few normal sigmas and no thick flagellosigmas. Type specimens were preserved in 95% ethanol and were deposited in the Atlantic Reference Centre (ARC) in St. Andrews, New Brunswick, Canada. The taxonomic identification was performed through spicule analysis using light and scanning electron microscopy, following methods described by Dinn et al. (2020).

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Deep-sea corals and sponges are a diverse group of habitat-structuring organisms found at continental slope depths in most of the world's ocean basins. Their distributions are influenced by oceanographic parameters such as temperature and salinity at coarse scales, and by surficial and bedrock geology and intermediate and fine scales. Recent remotely operated vehicle (ROV) video surveys focusing on twelve cold-water coral and sponge habitat sites in the northern Labrador Sea and Baffin Bay, Canada, were accompanied by acquisition of multibeam sonar and sub-bottom profiles, enabling analysis of the geological features upon which the coral and sponge habitats have grown. CTD casts in the same locations gathered data on temperature, salinity, seawater density, nutrient concentrations, and calcium carbonate saturation state. Most of the Northern Labrador Sea coral and sponge habitats are developed on glacially deposited materials. On the NE Saglek Bank, the site with the highest abundance of large gorgonian corals in the region, a diverse coral fauna occurs on current-swept bouldery gravels of glacial or glaciofluvial origin, with channels resembling glacial outwash fan channels between 300 and 400 m water depth. Further north in the Labrador Sea, near the Hatton Basin, SE Baffin shelf and slope, and Cape Dyer sites, diverse sponge-rich habitats appear to be most common on ice-contact bouldery gravels that have been extensively scoured by icebergs. On the outer side of the Hatton Basin sill, Primnoa resedaeformis-rich coral faunas are well developed on bouldery gravels that are interpreted as the grounding-line facies. CTD profiles at some of these northern Labrador Sea locations suggest sharp thermoclines associated with water mass boundaries, which likely also influence the distribution of the corals. Dense Keratoisis sp. bamboo corals in SE Baffin Bay are developed on muddy bottoms overlying a trough-mouth fan in SE Baffin Bay. Although the bamboo corals baffle sediments, creating small-scale topography, the ridges observed in multibeam and sub-bottom profile are glaciomarine in origin, likely till-tongues or glacigenic debris flows. Multibeam sonar and sub-bottom profiles were used to examine the geology of two sites with reported possible cold-seep related mounds, on the NE Saglek Bank and the SE Hatton Basin. Both sites are found within the iceberg-scoured ice-contact sediment facies. No evidence of authigenic carbonates or cold-seep related mounds was observed in multibeam sonar, sub-bottom profile, or box-core. Multibeam and sub-bottom profiles of the reported possible mound field in SE Hatton Basin revealed an iceberg-scoured ice-contact bouldery gravel facies, consistent with that observed at the NE Hatton basin sponge-dominated site. Methane bubbles and microbial mats were confirmed at a known hydrocarbon seep from Scott Inlet, in NW Baffin Bay. Bedrock exposures along cliffs in Scott Inlet support abundant Cladorhiza carnivorous sponges. Diverse sponge gardens were found on rill-and-gully morphology glaciomarine gravelly sands in SW Baffin Bay. The species composition of these sponge gardens appears to be quite different from that found in the northern Labrador Sea and in Frobisher Bay. Both the coral and sponge gardens contribute to benthic biodiversity throughout the region.