Cuttlefish, despite their name, are not fish but mollusks. They belong to the class, Cephalopoda, which also includes squid, octopuses, and nautiluses.
They have large w-shaped pupils, eight arms, and two tentacles with denticulated suckers, which they use to secure prey. Internally they have a unique shell, called the cuttlebone. They range in size from 15-25 cm (5.9″-9.8″) to 50cm (20″). The largest species, Sepia apama, weighs over 10.5 kg (23 lbs).
They eat a variety of small mollusks, crabs, shrimp, fish, worms, octopus and other members of their species. Their predators include sharks, fish, seals, dolphins and seabirds.
Interestingly, they have one of the largest brain-to-body size ratios of all invertebrates, and recent studies show that they are among the most intelligent invertebrates.
They are sometimes referred to as the “chameleons of the sea” because of their remarkable ability to rapidly alter their skin color. They can change the color, pattern and shape of the skin to communicate to other cuttlefish, to camouflage themselves, and as a deimatic display to warn off potential predators. Learn more about cuttlefish here.