Octopuses have long captured the imagination of ocean lovers, and it's easy to see why. They have a unique appearance and move through the water alienly. In addition, they produce clouds of smoky ink to defend themselves.

Unsurprisingly, they've inspired stories for years, giving rise to myths such as the Kraken and Ursula in The Little Mermaid. 

The oldest known octopus fossil belongs to an animal that lived some 296 million years ago, during the Carboniferous period. That specimen belongs to a species named Pohlsepia and is on display at the Field Museum in Chicago.

The word októpus in Greek translates to "eight-foot," and scientists have long thought that all octopus limbs performed similar functions. However, research has shown that some octopuses use two limbs for walking.

These rear limbs allow octopuses to walk across the ocean floor, similar to how humans walk on land. This leaves the remaining limbs free to form a variety of shapes. These shapes can include impersonating floating algae or coconut shells, which may protect the Octopus from predators.

Their unique nervous system allows them to perform multiple tasks simultaneously. Around one-third of their nerve cells are in their central brain, while an astounding two-thirds are in their limbs. In addition, each limb has its own nerve cell collection that enables it to move without input from the central brain. 

These flexible, highly specialized limbs enable octopuses to perform unique tasks. Like chimpanzees, dolphins, and crows, octopuses are among the unique intelligent animals observed using tools. 

To survive in the deep ocean, octopuses evolved a copper rather than iron-based blood called Hemocyanin, which turns their blood blue. This copper base is more efficient at transporting oxygen than hemoglobin when the water temperature is very low and little oxygen is around. 

Hemocyanin doesn't transport oxygen as well as hemoglobin, so octopuses need three hearts to deliver enough oxygen around the body. Two pump blood to their gills, and a third heart keeps circulation flowing to the organs. Unfortunately, this third heart stops every time the Octopus swims, which may explain why they prefer to crawl.