Missing arms would not affect its ability to swim or crawl. It is not unusual for octopuses to loose parts of arms (or detach a large segment) in the wild as it pokes into rockwork looking for food but be sure you don't have some other potential danger like an impeller that can be reached. I always disable the large claws on the male fiddler crabs to avoid puncture wounds (and potential infection) but I am not sure they can cut off an arm.
If your avatar is the same species (Wunderpus photogenicus), you may be in for a short run with the animal as very few do well in captivity. The arm truncation may be from stress. Watch carefully for more arms being lost and be sure it has plenty of dark hiding places.
Arm regrowth time depends a lot on the age and health of the octo. In very young animals, full regrowth can be as short as a couple of weeks. Adults may take more than a month and the new growth may never fully grow to match the other arms in girth.
To observe new growth watch for a thin string sprouting from the damaged tip.[/QUOTE
Thank you for the wise words, unfortunately the Wunderpus didn't make it. This was my first attempt at keeping an octopus, I should have started with something easier, or at least more adaptable to living in captivity. I did a TON of research, fastidiously monitored the water, tried to do everything right, but I'm afraid I may have gotten in over my head anyway. Do you have any suggestions for another species, something that would do better in captivity? I know the Bimac is very popular and easier to keep, I'm thinking of something... how should I say it delicately, maybe more aesthetically pleasing. I'm totally hooked, octopuses are the most fascinating, fun animals to have as pets, I just want to make sure I'm a responsible "octo-dad." Thanks again, I appreciate your help.