My husband used to have a ton of these in his tank, I just checked and there are a few, he has a clown and huma huma trigger, a sailfin, birdnose wrasse, snowflake, and small hawk so it's possible that one of the ones added last eats these things because now there only here and there. If it's the same thing it's not aptasia, it's tiny but a tube shape with something feather like coming out of the end, like microscopic feather dusters.