What animal has three hearts?

According to About.com, the octopus has three hearts, two of which pump blood through the gills of the octopus and another that pumps blood throughout the rest of the body. Octopuses belong to the phylum Mollusca and the class Cephalopoda, which includes squids, cuttlefish and nautiluses.

Octopuses feature eight arms and are bilaterally symmetrical. Lacking any kind of skeleton, the octopus is capable of contorting its shape and size to fit through structures much smaller than it is. As highly intelligent invertebrates, some species of octopus are capable of using tools. Octopuses may resort to camouflage and mimicry in order to evade predators.