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Hmm -- two or three years ago I was there and there was a beautiful GPO which I'm pretty sure was not King Tut. I believe Tintenfisch would know best, she used to work there and I believe stays in touch. Also, did you try their website?
The NEAq generally has a GPO (Enteroctopus dolfleini) and they reach pretty good size. When I was there last November, Sebastian (King Tut's successor) was on his last legs (arms?) and I met his replacement, waiting in the wings, who hadn't been named yet but was already quite large. So... whether you'll see a really old one or quite a young one I'm not sure, but there should definitely be one on display. Find out its name for us if you get the chance.
They also go through phases of keeping cuttlefish, and you can almost certainly see chambered nautilus, although this exhibit is very easy to miss - it's 'hidden' (i.e. recessed and quite dark) on the first floor just as you go out to see the seals & sealions.