Sepia plana is a species of cuttlefish native to the coast of Australia, specifically the North West Shelf (12°04′S 122°59′E / 12.067°S 122.983°E to 17°55.5′S 118°16.0′E / 17.9250°S 118.2667°E). However, cuttlebones of this species have also been found off eastern Australia, suggesting that it may have a wider distribution. S. plana lives at depths of between 396 and 505 m. S. plana exhibits sexual dimorphism, as females grow considerably larger than males. They reach a mantle length of 151 mm and 99 mm, respectively.