Morphological measurements and video annotation of the new octocoral Swiftia phaeton sp. nov. during the cruise MSM 16-3 Phaeton in 2010 off the Mauritanian Slope

Swiftia phaeton, a new species, is described for Mauritania where it is endemic at the upper bathyal. This azooxanthellate octocoral is distinctive from congeneric species in the NE Atlantic and Mediterranean Sea by the dark red coloration of the colonies and polyps, the presence of a layer of rod sclerites on top of the calyces and different sizes of polyps and sclerites. Coral gardens dominated by a species of the genus Swiftia Duchassaing & Michelotti, 1864 were filmed for the first time it the southern NE Atlantic Ocean. The extensive Swiftia phaeton sp. nov. dominated habitats were recorded during the Phaeton expedition onboard Maria S. Merian in 2010 at the Mauritanian Slope between 20°24N and 17°54N in 470 - 640 m depth, co-occurring with the framework-forming scleractinians Lophelia pertusa (Linnaeus, 1758) and Madrepora oculata (Linnaeus, 1758). ROV video annotation based on size and density distribution of Swiftia enabled the characterization of the new biotope.