The knifetooth dogfish, Scymnodon ringens, is a harmless sleeper shark of the family Somniosidae, found in the eastern Atlantic, from Scotland to Spain, Portugal, and Senegal, and the southwest Pacific from New Zealand, between latitudes 58°N and 15°N, at depths of between 200 and 1,600 m.
The smallmouth knifetooth dogfish, Scymnodon obscurus, is a harmless sleeper shark of the family Somniosidae, found in the central Atlantic between latitudes 65°N and 36°S, from the surface to 1,450 m.