Good stuff, I wish I had the skill and heart to do this when they die. I DO photograph and measure (@sedna started this some years ago and several of us have continued the practice). The measurements are always notably smaller than when they are alive but gives a consistent state for measuring. The chromatophore firing after death is seen most of the time and always a little freaky when trying to set them up for final photos. In one animal, I videoed the the reaction.
I never (and really regret it - tried to take it as my lab in college but nursing students filled the classes and had top priority) took more than one year of high school biology so would have a hard time identifying anything inside since the real animal does not look a lot like the sketches BUT there is one additional clue that you have uncovered, this is a large egg species and raising them in an aquarium may be viable IF one could get the female to lay eggs. I did not see any spermatophores but am not sure what it would look like if they were spermatangia (out of the casing - my new word from the Giant Squid dissection). As far as we know most squid and octopuses (but this may not be true of all species) don't fertilize eggs until they are laid so it is not likely these were fertile (and she may not have even mated).
I am not sure you would see blood the blue coloration is very faint and I don't know if it changes like ours (or to what color) when exposed to oxygen in the air.
Lost the male a few days ago and stopped by the store again this morning.m they had a new shipment in and there were a couple of octopuses at had crawled out of the shipping bag and were wandering around the tank. These were exhibiting more movement than any I have seen there so far so I picked up three that were moving around a lot and am acclimating them to the system now.
Just released them, identified two males and a probable,female (arm is missing the tip, but regrowth appears to be regular arm versus a hectocotylus. Two hid immediately on release and the third went I to a corner behind a shell. Previous attempts in this round of octopuses have pretty much gone in and fallen to the bottom.
I turned the lights off and left some red lighting on, will see how they appear later on. Some good signs beyond the hiding and one crawling out of the bag are that their eyes are not hidden away and coloration looks good, too.
Found a video of a guy catching nakji on a mudflat in South Korea. Nakji is the term for small octopus that are eaten alive in Korea, not sure if it refers to a species name, but now I am thinking this is not a cold water species but should be kept in the 60-70 degrees Fahrenheit range. Have not had a mud tank before and probably will not attempt to change the substrate out at this juncture, but am slowly adjusting the temperature up for these guys to see what the result is. I would rather not change it drastically, but a degree every day or two might be in order. The temp I recorded from their store was around the mid 50s and the bag was 56 when I got home so I am setting it to 57 and will raise it up again tomorrow another degree. Hopefully this will not prove to be too much but if they are being kept colder than they are able to handle, I think e dangers might be the same. Unfortunately, trial and error is probably the only way to do this for the time being with a lack of any species identification or information...
I was worried last time and this as well that the temps you are seeing with them are more for shipping than habitat but without species info I think your approach is about all you can do. Thinking out loud, we know they have survived with temps in the 50's so they are probably not warm water (75-80) animals but they have been listless and not survived long at shipping temps so your guess at an appropriate range seems to be a good target. If your chiller is like mine, there is a 4 degree variance (2 on either side) allowed so I would set the temp +2 or +3 degrees to start the upward temps.
I set it to a +/- of 1 degree as I don't want it to swing that much. If it misses the mark and chills too far down, it makes for a temperature swing of up to 3 degrees. Will have to wait and see, though. What's your thought on maximum change in a day? You mentioned +2 or 3 but is that potentially too much in a day?
I am guessing that a normal day/night temp swing should be a good choice. I made an assumption that the ocean temps change at least 2 degrees but realized I did not "KNOW" that from anything other than perceived cooling that can be more air temp than water temp. I found a NOAA site that should be somewhat helpful to get a feel for the daily range. 2 degrees turns out to be a pretty good guess but there is more info there that might be helpful. This is for the US and you can click on the various areas to get more info. Clicking on the given temps will give you a daily range chart (where available). I briefly looked at the East coast but the West may be more similar.
Found a site that gives average sea temps indicating that at the coastal city of Busan where they eat a lot of these the low is around 55 in March to a high of almost 80 in August.
One male that is missing an arm and has another that has some significant damage about halfway up looks like it will not survive. It is not moving a lot and doesn't respond much to stimuli.
The other male looks to be doing pretty well. It was out and about and exhibited so e deeper coloration than the others which extended to below its arms as well. Not necessarily what I believe to be angry colors, but certainly not the flat greyish white that most have exhibited.
The female seems to be doing okay as well but not sure of this. She is, however, digging down into the substrate and pushing a lot of sand around. If this is the species from South Korea found in burrows in the mudflats, then this could be natural behavior.
There are two crayfish living in the system with them right now, neither has been touched yet. I have offered a red claw crab, pieces of shrimp, and the aforementioned crayfish. I may also try a piece of smelt or small silversides as well. Clams and snails don't seem to have fallen prey to any of his batch so far, either.