The picture is not too helpful (you were supposed to tell it to pose and smile ) but the striping would be right for a CCR (common Caribbean Reef Octopus aka O. briareus) and the general look is right. Hopefully you have more pictures now that you can post. Typically this species is weird about acclimation and will not leave its acclimation chamber (bag, jar, critter keeper) until it is left alone in the dark for awhile (sometimes several hours). If you use a bag, you might slit it to be sure it does not end up suffocating itself (might be a little late now I am afraid but I am sure you are watching it). I prefer to put them in a critter keeper with drilled holes because of this oddity (when I don't get them in a drilled jar - one way my main supplier will ship often them).
Oh, and about the coin. Put it UNDER the container next time, not IN it
Robyn, O. briareus can have pretty thick, strong arms. The reason we don't see it much is that they stick them into every crevice they can manage and often come up shortened. Blake's octo (the referenced link) is a really good example. The one very long arm is the only one that is normal, the others have supplied something else with a meal. Not all arms are the same length naturally though and the back ones are shorter but still stout if tank raised or caught very young but even the very young ones will have arm damage from their foraging behavior (undetectable as they grow). I recall making comments on some of my photos/videos where they are checking out the LR even though they are not hungry.
so i apologize for not posting, mostly because it was a bit of a stressful fight, and not pretty. but after 11 days, i found the Octo dead this morning... I felt that the 55 gallon tank may not have been big enough for the animal. I still want to keep an octo, next ill be more selective about the species, trying to go for the pygmy octo, or at least a younger one that can grow into the tank.
I am glad you were willing to make the journal entry. I try to record longevity in our list chart and so often keepers are so bummed out that they do not make the final post (and I too lag in the post even though I always take a measurement photo the day of the death and often preserve the animals for students that come inquiring). Octo keeping and collection for the aquaria is still a very new area in a new industry and without some kind of recording we have difficulty learning. Collectors hand off a live animal and that is the end of their information. Similarly, a seller without a 14 day guarantee, never knows how well the animal survives. Some sellers will explicitly exclude octopuses from their arrive alive or longevity refund.
A 55 is small for most (they do vary widely in size) O. briareus but I don't think this was the problem unless your water quality was an issue. I don't think it was the coin exposure either but put it underneath next time or use something plastic. This was not a very young animal but the strength of the coloring suggests it was not well into senescence. As O. briareus enters the final stage it is very often a grayish white and cannot hold patterning for any length of time. Its arm muscles will be much reduced and quite weak but this is much easier to identify in animal that has been tank raised than in one that was recently introduced. Age may have played a part in its inability to acclimate and this can work against an old or a very young animal.
I started to post that the color was odd for a white background (I had also initially confused this one with Genghis) but went back to some of my own acclimation photos and realized that this is not odd for adults and even some of my little guys have displayed the mottling. I've lost a small number of animals during the first two weeks without being able to define the reason. A full two weeks seems to be the initial telling point (I have actually lost one on day 14). IME, full acclimation takes about a month and I don't consider an animal established until it takes a den and then defends it by waving its arms around in warning when I clean the tank.