This is pretty nifty: it’s a nine-tentacled octopus. Count ’em!
If I may be so bold as to remind you all of the basics of cephalopod development and evolution, the primitive condition in cephalopods is to form ten arms; in the octopods, one pair is secondarily lost by some unidentified suppression in development. It’s not too surprising that there would be some low frequency of re-expression of members of the fifth and normally missing pair — and the article mentions that the Akashi Seafood Council reports that they see this once in every 20 years or so.
They should keep an eye open for these kinds of developmental abnormalities — they can be an indicator of stressors in the environment if the frequency starts to rise.