Octopus
 
As it is difficult to determine between different species of octopus I have not given it a Latin or common name.
Octopus have their own permanent burrow (that is why the diveguides always seem to find them).  Just like the cuttlefish they have an amazing ability to camouflage themselves when they are out and about. Once discovered they might have a closer look at you by touching your hand with one or two of their eight arms.
If you are not sure about the species you are encountering be careful not to aggravate a blue ringed octopus!