I will add to this thread to take somewhat a different view.
In speaking from personal experience, I have not had an anemone die yet, that wasn't sucked up in a powerhead. I believe they are very cool creatures. I have 4 different breeds within my tank, and all are thriving. I am not saying that what I have and the success so far, will work for anyone else, but hey, it's working for me. I do have a good amount of lighting, and the tank is mature. Clownfish are beautiful fish, and though most say they do not need an anemone to host, I believe it to be false. I can't think of anything more un-natural than a tank with a clown, and nothing for it to form a symbiotic relationship with. They will however, take to certain soft corals such as xenia, ricordia mushrooms, leathers, etc.. and use them as a host. Most, (and I respect their decisions), disagree with using anemones in tanks merely because they are scarcely tank raised and you would be getting them wild caught and thus deminishing reef life...This is to be respected. I bought mine before thinking coherently
I have a Tomato Clown and I think he is cool, after buying a Carpet Anemone, he has decided to use my Florida Ricordia Mushrooms as a host and is quite happy. So, I think the hypothesis is, yes Clowns do need something to form a symbiotic relationship in, whether it be an Anemone or a Coral of some sort.
And to further that, I think it is man's decision to say that Clowns do not need a host. It was deemed by mother nature that they do this, and no matter how much you breed them in tanks, they still have that instinct. It does not get bred out of them. Think of it as animals in captivity such as a Lion. Yes, they were wild caught, bred in captivity, and even though raised by humans, they will still gain a taste for our butts and eat us if given half a chance. Instinct does not get bred out. It is alive and well. Why do you think they keep them in zoos, and not sell them as pets after all these years of captive breeding. So in closing, IMO
, to say that one of mother natures creatures does not need what it was designed to be with, it proposterous and un-natural.