Sepia mestus, also known as the Reaper cuttlefish or simply Red cuttlefish, is a species of cuttlefish native to the southwestern Pacific Ocean, specifically Escape Reef off Queensland (15°47′S 145°47′E / 15.783°S 145.783°E) to Murrays Beach off Jervis Bay (35°08′S 150°46′E / 35.133°S 150.767°E). Reports of this species from China and Vietnam are now known to be misidentifications. S. mestus lives at a depth of between 0 and 22 m. S. mestus exhibits sexual dimorphism. Females grow to a mantle length (ML) of 124 mm, while males do not exceed 77 mm ML.