Humm, the color markings would be odd for a merc but I have never put one on black gravel
. The mantle looks twice the width I would expect, the green is not normal but I have seen blue on a merc once, there are more cirri than mercs usually show but they are very low, and the webbing looks too deep as well. However the photo angle may forshorten the mantle and account for the appearance of the webbing.
I do think it is a dwarf species and likely nocturnal but am less inclined to think merc from these last photos. Keep taking photos and watching colors and skin texture. I had an absolutely lovely animal that was a diurnal dwarf and was never clear on its species. See what photos your can find for O. burryi (other than Monty's as that ID is not strong).
OK, my best guess is O. burryi. There are not a lot of pictures but it would be local to your area and fit the second set of pictures well.
Here is one photo I did find.
Here are two papers I found while trying to ID Monty. When you go to the linked abstracts, click on the PDF icon. They are free to view.
If
Monty WAS O. burryi (and I am inclinded to think so, especially after rereading the abstract that mentions a poorly defined eyespot - except his was only poorly defined most of the time, at others it was quite clear
), this is an excellent octopus for the home aquarium and I would like to have others. It works well in a 35 - 40 gallon tank (possibly smaller but he used all of his tank but never attempted escape (IMe escape attempts are often because a tank is too small). Patterning and colors were exceptional for a dwarf and he was diurnal. The paper mentions burying but Monty lived in the LR and I never saw him attempt to bury.