Rock anemones (Epicystis crucifer) reproduces sexually in aquaria on rare occasion, but I've never heard of a natural fission. They are not natural hosts to any of the clownfish, but I have seen pictures of maroon clowns in E. crucifer. They are from the Atlantic/caribbean where there are not clownfish. I would say there might be a small chance the anemone would eat such a clown, especially if it is small. I believe porcelain crabs will be hosted by rock anemones.
