The natural hosts would include magnifica and gigantea. However, neither of those species are especially easy to find healthy, thus the success rate is relatively low with each. The good thing about mags and gigs and ocellaris is that you're almost certain to have a very quick symbiotic relationship. I know with mags they pretty much swim directly into them as soon as they are placed together in a tank. BTAs are a much easier anemone to keep and often ocellaris will at some point take to the BTAs, it's just not a certainty as with a magnifica.