Octopuses are a group of animals that have eight arms. They are cold-blooded, so they cannot generate heat internally and relies on the temperatures of its surroundings. Also, they have nine brains, with one brain, the largest one and is located in the head, having the job of commanding the eight other brains, it's quite intelligent, the eight other brains, which are smaller and are located near the arms, recieve its commands from the commander brain. Their main purpose is to control the octopuses arms. However, sometimes, the eight smaller brains can't cooperate with the big one, resulting in the arms moving independantly.
Octopuses, like other sea creatures, breathe underwater through gills, organs that extract dissolved Oxygen (O2) molecules in Oxygen-rich Water. Oddly (actually just about every feature the octopus has is odd), they have three hearts, two of them are used to pass blood exclusively through or to the gills.
Octopuses have short life-spans too, usually at maximum 1-4 years, some species even have a maximum lifespan of 3 months! Not only that, when a male octopus mate with a female one, he dies, since his sex arm (the longest arm that contains sperms) is torn off from him (the male one) by the female after the male injected his sperms to into the female. Without his sex arm, the male cannot live. The female, however, doesn't even notice the male dying, instead, it carefully takes care of it's un-hatched eggs. Sadly, the female also dies when the eggs hatch due to her optic glands sending out self-destruct hormones.