Cuttlefish!

Cuttlefish are molluscs with an internal shell - cuttlebone, eight arms and two tentacles furnished with denticulated suckers with which they capture their prey. 

They are among the most intelligent invertebrates with a very big brain-to-body size ratio.

They eat small fishes, molluscs, octopuses and other cuttlefishes as well.

Their skin made them gain the name 'chameleon of the sea' to camouflage and their eyes have no blind spot as the optical nerve is just behind the retina. 

Curious thing to know is that they have three hearts.

In order to defend themselves, they spit ink, which may be of no harms to very deadly and lethal.