Squid, octopus and cuttlefish belong to a large group of marine invertebrates called cephalopods. The word means foot-headed, and it is an appropriate name for these creatures because their tentacle feet sprout from above their eyes and brain. They are found all over, and sometimes in the stomachs of whales that has just finished lunch.

There are more than 500 varieties of squid and cuttlefish, of which two dozen are commonly eaten around the world. About half the total global squid haul is caught and consumed in Japan. To supplement the native catch an additional 200,000 tons are imported, mostly from Australia and New Zealand, making up one-third of the Japanese market.

The Japanese word ika does not distinguish between squid and cuttlefish. The flesh of the two is similar; the anatomy differing in the shape and composition of the inner shell. In squid, this hard plastic-like shell is called a pen. Cuttlefish have a more substantial inner shell, referred to as a bone. This cuttlebone has several commercial uses, while the squid's pen is generally thrown out.