Squid is not a fish.

Cuttlefish is taxonomically classified as shellfish and is a mollusk. It has shells on its body, but because its lifestyle is different from other shellfish, its physiological structure has slowly changed.

Most shellfish have very little mobility, but cuttlefish have special swimming abilities.

In order to adapt to this swimming lifestyle, during the long evolution process, the cuttlefish shells gradually degraded, and were finally completely wrapped in the mantle, turning into the "backbone" to support the body. "Yes.