Interesting. While we're off topic, they're also delicious. Slightly sweeter than squid and I find less prone to going tough. They take a little bit of preparation but you get quite a good size meal out of a single one. As a bonus they grow quickly so are a fairly low impact species to take.
They are also used as a calcium supplement for animals:
"Today, cuttlebones are commonly used as calcium-rich dietary supplements for caged birds, chinchillas, hermit crabs, reptiles, shrimp, and snails. It is not for human consumption"