I think this is one of those groups where a lot of species have been kept short term for research or imported for the aquarium trade but never gone on public display and/or maintained long term. For example I know that the mimic octopus ( Thaumoctopus mimicus) has been kept in captivity and has even been seen in UK aquatic stores (but not by me!) but I don't know whether any have ever gone on display in a public aquarium
Yeah, I know Mimic Octopus are in the private trade, but this list is for public aquariums/zoos (I should have clarified that).Mimic Octopus is missing from the list. Not sure if any zoos have them but they are around in the private trade.