Complete answer:
Cuttlefish are the molluscs of the Sepiida order, which belongs to cephalopod class. They are not considered as true fish because they don't have bones, heart and brain.
Why are cuttlefish not fish?
Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda, which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone. Despite their name, cuttlefish are not fish but molluscs.
Which one is a true fish whale cuttlefish?
Note: Whereas a whale is a mammal. Cuttlefish are mollusks. Silverfish is an arthropod. Flying fish is genuine fish.
