Unlike other squids, their coat is usually more dull and less cuneiform. But the most fundamental difference is the shape of their inner skeleton, which is formed like a flat bowl of limestone. This bowl contains numerous gas-filled chambers, which help with buoyancy.
Like most cuttlefish the sepia has a horn-like beak. There are ten tentacles around its mouth, which are usually relatively short. The longer tentacles, which they use for hunting, are hidden between the tentacle arms when at rest.
Sepia are lurking hunters but aren't as fast moving as squids. Their main propulsion is generated by their fin edging, which runs around their whole body like a band. Its wave-like motion propels it forward. In the face of danger, like squids, they squeeze water out of their coat tube to get away in a hurry.