...it must be a cephalopod mollusc of the order Octopoda. Or in plain English: an octopus!
Going one better than a Time Lord an octopus has three hearts but they cannot regenerate and, as many species have a very short life expectancy of only 6 months, I think the Doctor probably wins in this game of top trumps. I'm rambling...
Anyway, my octopus still does not have a finished body (I got distracted by all the brightly coloured images in my laptop) but it does have all it's arms and I consider that an achievement.
Next question is what to call him/her, I did briefly flirt with Octavius as I was looking for an alliterative name but I'm not so sure now. Any ideas folks? And don't all rush to suggest your own name!