Ascarosepion mestus, also known as the reaper cuttlefish or red cuttlefish, is a species of cuttlefish native to the southwestern Pacific Ocean, specifically Escape Reef off Queensland (15°47′S 145°47′E) to Murrays Beach off Jervis Bay (35°08′S 150°46′E). Reports of this species from China and Vietnam are now known to be misidentifications. A. mestus lives at a depth of between 0 and 22 m. Ascarosepion mestus exhibits sexual dimorphism. Females grow to a mantle length (ML) of 124 millimetres (4.9 in), while males do not exceed 77 mm (3.0 in) ML. The type specimen was collected off the Australian coast and is deposited at The Natural History Museum in London. Ascarosepion was revived as a genus in 2023; as the genus was named using a specimen of this species, Sepia mestus is thus the type species of Ascarosepion.

Anatomy Cuttlefish generally share many similar anatomical structures and it can be hard to distinguish between different species in certain situations. Generally, cuttlefish can be diagnosed posthumously based on mantle shape and the structure of their tentacular clubs, which remain concealed in life. All cephalopods have a similar basic anatomical plan. Structures include a set of limbs that diverge from the head in a ring around the mouth.