Octopus

The octopus is a mollusk with 8 arms. It has no internal or external skeleton, allowing it to squeeze through tight places, for example crevices in the coral reef. They hunt at night and seek shelter at daytime, making them difficult to find. 

Octopuses are among the most intelligent and behaviorally flexible of all invertebrates. They can also change color at will. I once saw an octopus change color from white to blue in less than a second.