A new species,
Longibrachium falcigerum, is described from seamounts in the North Atlantic Ocean, from depths of 495–695 m.
Longibrachium falcigerum sp. nov. is unique among its congeners for possessing falcigers and spinigers in the lower chaetal bundle. Another member of the
Rhamphobrachium complex,
Rhamphobrachium (Spinigerium) brevibrachiatum, occurring with the new species, is briefly characterized.