In nature, it is quite rare to encounter octopi with extra tentacles (or "arms," for the purists), but a pair of aquariums in Japan's Mie prefecture have some extraordinary specimens on hand.
The permanent display at the Shima Marineland Aquarium in the town of Shima includes a 96-tentacled Common Octopus (Octopus vulgaris) that weighed 3.3 kilograms (about 7 lbs) and measured 90 centimeters (3 ft) long when it was captured in nearby Matoya Bay in December 1998. Before dying 5 months later, the creature laid eggs, making it the first known extra-tentacled octopus to do so in captivity. All the baby octopi hatched with the normal number of tentacles, but unfortunately they only survived a month.
The preserved octopus actually has the normal number of 8 appendages attached to its body, but each one branches out to form the multitude of extra tentacles. Apparently there is no theory that fully explains the surplus tentacles, but they are believed to be the result of abnormal regeneration that occurred after the octopus suffered some sort of injury. … – see the full article pinktentacle for another pic and more.