I am guessing a nocturnal dwarf species based upon the eyes but am stumped on species (especially if it has only one row of suckers, we don't see that often). I am also guessing adult because of the mantle indent. I have recently noticed on my O. briareus that this dent does not show until they are more than half grown but need to watch for it closely and try to record exactly when I first see it. I have gone back through photos but don't have an accurate feel for when it shows up (it may be different for different species and may not be relavent. I have no clue what causes it biologically).
Does it show any special markings, like a yellow line down the back of its mantle?
There is one we never see that is very common and sold as "baby octopus" in the markets. If it is Octopus aegina (I think the genus has changed several times now but the species remains aegina) or the "Marbled Octopus", you should see a thin yellow (or pale) stripe donw the back of the mantle and sometimes just above the eyes. The photos in Cephalopods A World Guide look very similar and the location is right but many of the on-line photos look significantly different. The stripe, however, would be a good indicator if you see it. From some of the photos I saw (if they are IDed correctly ), it it has an excellent repitoire of patterns.
OB, I could not (and still can't ) tell. One arm might be showing two rows but the second row could be from another arm. There are not many with single rows though (at least not from where we would see them) so I spent a lot of time looking and only came up with one possibility in a cooking article that pointed to a macropus that is "inferior" to the aegina . I could not find such a macropus in any of the more scientific offerings though
The eyes are what make me think the aegina is a possibility. The additional info about a splotchy pattern would also fit the "marbled" common name but the stripe is the only diagnostic I could find.
Yes the two rows of suckers are alternating. it's size now is about three inches from arm tip to tip. I haven't seen a stripe yet but it's difficult to get good views without making it mad, then it just goes a deep brown/red.
O. aegina would sometimes show distinct thin brown lines on the arms. In the wild it's been known to mimic a flounder, like its more well known cousin Thaumoctopus mimicus. It is also a muck dweller, FYI, when contemplating substrate, should the ID turn out to be correct.
With it being so small, I am backing off that guess and going more toward one of the first animals I looked up. I am not thinking O. bocki looks more realisitic if I am right about it being an adult. The brown red color would makd more sense but the arms seem too long in proportion to the mantle (I am estimating a 4:1 arm:mantle relationship from the photo).
I am wondering why we don't see aegina though as it is common and nicely sized for the hobby.