Rhamphobrachium (Rhamphobrachium) agassizii is reported from the Cantabrian Sea, Spain, from depths of 925–1207 m. This is its first record off the Iberian Peninsula and in European waters, representing its northernmost distribution in the North Atlantic Ocean to date. Previous reports of R. (R.) agassizii from the eastern and western North Atlantic demonstrate its apparent amphi-Atlantic distribution, which appears consistent with the distribution of the main Atlantic currents. It is a typical deep-water species with its deepest record at 2165 m from the Azores archipelago. The specimens were collected singly at two stations, attesting to the rarity of the species in contrast to its congener R. (Spinigerium) brevibrachiatum which was the most dominant polychaete species in a previous study.

A new suprabenthic mysid, Mysidopsis cachuchoensis sp. nov., is described from specimens sampled with a suprabenthic sled at the ‘Le Danois' Bank (the ‘El Cachucho' Marine Protected Area; southern Bay of Biscay). The main distinguishing features of this new species are the structure of its eyestalk and antennal scale as well as the armature of its telson and uropodal endopods. Inferred from the present unique record (828 m depth, inner basin between the bank and the Cantabrian shelf), it seems to be a rare endemic species of the bank, living on muddy bottoms of the upper bathyal.

A new bathyal leucothoid amphipod, Leucothoe cathalaa sp. nov., is described and illustrated based on specimens collected at the Le Danois Bank (‘El Cachucho’ Marine Protected Area), southern Bay of Biscay. This species can be distinguished from the other species of the genus Leucothoe by the hardly visible eyes (translucent ocelli, in preserved specimens); antenna 1 with minute accessory flagellum; coxae 1–3 with 2 serrations on posterodistal margin; epimeron 3 posterodistal corner produced, bifid, with one seta between blunt lobes and telson apex pointed without accessory teeth. In live specimens, the eyes are easily visible, each represented as a rounded whitish-pigmented spot. The new species has been found living on fine sandy soft-bottoms between 486 and 574 m depth at the top of the bank. An identification key to the deep Atlantic European species of Leucothoe is provided, as well as ecological and biological comments.