| Summary: | Deep-waters are one of the most unknown habitats on Earth, but the displacement of fishing fleets into ever deeper waters, the emerging exploitation of mineral resources and climate change threaten to destroy these ecosystems whose functioning we just begin to understand (Levin & Sibuet, 2012). Superfamily Plumularioidea is the most important group of deep-water Hydrozoa, both in species richness and abundance. In spite of being typical epifauna living on hard substrates, many species also colonize soft bottoms by adaptions on their hydrorhiza. The morphology of their colonies, feather shaped, often branched, and with sizes that can exceed one meter length, contributes effectively to the development of a three-dimensional habitat and provide secondary substrata for other hydrozoans (auto-epizoism sensu Millard, 1973) and for other invertebrates (see Ansín Agis et al., 2001), thus enhancing the biodiversity. This communication deals with the results of the study of this superfamily in the continental margin of Mauritania, between 80 and 2,000 m depth. Samples were collected in 329 trawling stations during the four multidisciplinary Spanish–Mauritanian surveys (Maurit) carried out from 2007 to 2010 onboard R/V Vizconde de Eza. Most samples were collected using a commercial trawl gear (Lofoten type) following a stratified random sampling methodology program. Moreover 25 stations were also sampled along five transects perpendicular to the coastline at five bathymetric strata with an Agassiz trawl, and 26 samples with a rock dredge were carried out over the cold-water coral reef, the canyon edges and the seamount. A total of 4,073 colonies of Plumularioidea were collected, and 20 species were identified; nine of them reported for the first time in Mauritanian waters. The greatest diversity corresponded to Plumulariidae family (8 species), followed by Aglaophenidae (6 species.), Halopterididae (4 species.) and Kirchenpaueriidae (2 species.). Most of them showed an eurybathic distribution and were collected along ...
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