I was out diving last Saturday, taking a couple of 12 year olds on their first ever dive in the sea. They had been under in a swimming pool but that is nothing as exciting as diving in the open sea. Now, sighting an octopus is pretty rare, I've only ever spotted a couple, but these kids got to see the biggest octopus I have come across on their first ever dive. I planned to stay down 30 minutes or so and it was towards the end of the dive that another instructor signaled to come and look at something. Just the luck of the draw sometimes.
The one we saw is a 'common reef' (Octopus Cyanea) octopus, though they are not easy to spot. They are masters of disguise and change colour to blen in with wherever they are.
Image below I just have taken from the web but the kids teacher was diving with the kids (about 10 in all with four of us instructors) and he was taking photos so I will try to get some off him when I see him again this weekend.