Katianira platyura, new species, is described from the mid-bathyal zone of the Kumano Basin, southern Japan, the first record for the family from the North Pacific. Katianira platyura differs from its congeners by having the head with a pair of broad, deeply divided, bilobed lappets; pereonite 1 laterally rounded; anterior and posterior corners of pereonites blunt; mandibular molar process rudimentary; pereopod 3 flattened and broad; distal part of pleopod 1 with 32 setae; protopod of pleopod 2 trapezoidal; tip of endopod of pleopod 2 reaching to approximately 0.9 of protopod; and broad, leaf-shaped uropods.