I would put (a small amount of) money on O. briareus. Its health is a concern but that may be more artifact from the photography than reality but it will be a nerve racking next two weeks. It has had its share of predation (not unusual) and has survived and seems to be ecovering normally from the loss of arms. What you will hope to see is a strong white most of the time but they can color in various shades of peachy brown and show small, almost fur like bumps on the mantle.
Typically, this species is difficult to get to leave the acclimation container (bag) and often "freezed" when first put into the tank. Once the tank is dark, they find a dark den and use it. Some will appear quite friendly the first week and I always recommend not expecting the same personality after 2 weeks. They can become friendly and interactive (huge variation in this species) but not when first introduced.
No sex clues are obvious. What you want to watch for is the third right arm (clockwise as you orient your eyes with those of the octopus) being carried curled when all the others are not. The curled arm tips here are from loss of the ends of the arm. I recently reread a paper on arm regeneration and would recommend it for reading. Of note is the orientation of the suckers when the arm first starts to grow and when it is well on its way to regenerating.
The refusal to enter the tank is pretty universal but only with this species Be sure the bag is not suffocating him/her as their breathing can draw it in. I use a critter keeper with a lot of holes rather than a bag because of the way it clings and the way O. briareus just waits until no one is watching in the dark to find its way around.
You may even want to slowly and carefully split open the bag with a pair of scissors to be sure it does not collapse on the octo.
I wish we had a list of suggestions but the first two weeks is pretty much a wait and see. USUALLY, if they make it the fist two weeks, they will live to senescence (which can be another week or months down the road). This is a pretty robust species but each animal is individual and I have lost a couple in the first week that I thought looked healthy.
The color pattern is not unusual but something about the overall look bothers me. I may well be the photograph more than the animal but there is a crispness/firmness that is missing to say it looks healthy.
Getting it to eat will be a next priority but not today. Today should be quiet and dark. If you have a live fiddler, put it in the tank (if male, break one part of the large claw so that it cannot puncture. It may drop the claw. Don't put the loose claw in the tank if it does as it is more a pollutant than food if not on the crab). If you don't have any small live crabs then don't worry with trying to feed today as it will more likely add more stress than any nourishment. I try offering food before release but more often than not they won't take it. Once I release them, I give them ~24 hours before trying to feed any form of dead food (usualy a piece of shrimp on a stick).
Any small crab is fine but I hate to use emeralds and some of the others as food both because of expense and because they are nice gentle clean up crews (I can just see Thales rolling is eyes ). I get my fiddlers from Paul Sachs because he always has them, is a reliable supplier and is relatively inexpensive. When I get near the coast, I buy them from bait stores and if my son and his wife happen to be visiting her mother and dad in Savannah and will be coming up our way soon after, I beg them to collect or buy (again at a bait store) for me If you want to make the trek up here, I have a few I can give you but with the price of gas, free makes them still expensive and I lost Octavia last night so I have no octopuses for you to see as a bonus.
Sorry to hear that. I bought four emeralds just to get me through the next couple of days. I'll go ahead and order Fiddlers. Octo is off the bag and pretty active. I will post a video as soon as I figure out how to.
Video will have to be hosted on something like YouTube (my personal choice), Vimeo, Flicker, etc. Once you have uploaded it, go to the video and copy the URL (DO NOT use the share or embed code provided). In a thread, click the film icon and paste the URL address in the pop-up (you may need to enable pop-ups and may have to click the film icon a second time if it was blocked originally). This will embed most videos but not all host streaming is compatible.