Octopus

Octopuses inhabit diverse regions of the ocean, including coral reefs, pelagic waters, and the ocean floor. They have numerous strategies for defending themselves against predators, including the expulsion of ink, the use of camouflage and deimatic displays, their ability to jet quickly through the water, and their ability to hide. They trail their eight arms behind them as they swim. All octopuses are venomous, but only one group, the blue-ringed octopus, is known to be deadly to humans.
The octopus has been shown to use tools. At least four specimens of the veined octopus (Amphioctopus marginatus) have been witnessed retrieving discarded coconut shells, flasks or ballots, manipulating them, to use as shelter.
Octopuses can use muscles in the skin to change the texture of their mantle to achieve a greater camouflage. In some species, the mantle can take on the spiky appearance of seaweed, or the scraggly, bumpy texture of a rock, among other disguises.
In classical Greece, Aristotle (384 BC – 322 BC) commented on the colour-changing abilities of the octopus, both for camouflage and for signalling, in his Historia animalium:
The octopus ... seeks its prey by so changing its colour as to render it like the colour of the stones adjacent to it; it does so also when alarmed.
— Aristotle