Sepiella japonica, the Japanese spineless cuttlefish, is a species of cuttlefish native to the western Pacific, around China, Japan, and South Korea. It has been an integral part of many seafood fishery industries but was nearly harvested to extinction due to anthropogenic damage to important habitat and overfishing. The conservation of this species has presented numerous complications as their migratory nature complicates typical protection strategies like the establishment of marine protected areas (MPAs). Their development is contingent upon the stops along their migration which has prompted further research to dive deeper into their behavior and environmental requirements and components continue to change as a consequence of climate change.

Description Sepiella japonica is a member of the Cephalopoda class, in the phylum Mollusca. Cuttlefish, in the order Sepiida, feature a large and comparatively flat mantle cavity which shelters their internal shell called the cuttlebone. Like other cuttlefish species, the cuttlebone is used to regulate the fish's buoyancy by storing gases between their septa dividers. This shell type is characteristic of cuttlefish species but often varies in shape between species. Despite being a member of the invertebrates, the term “spineless” is actually in reference to the morphology of their internal cuttlebone. Similar to other decapodiformes, they also have 10 limbs, 8 of which are arms, and the remaining two are tentacles lined with suckers for improved utility.