Sexual reproduction of rock anemones, and cnidarians in general, isn't very common in captivity. Most cnidarians release both eggs and sperm, which combine to form a small planula (free swimming baby coral). This doesn't often happen in captivity, and when it does,, standard aquarium filtration usually removes the planual. With rock anemones, the female’s eggs are fertilized internally. She then broods the little ones until they are a bit smaller than a pea and then releases them. This is pretty rare in captivity. Last week I found a bunch of little ones all around mom in her cup. Mom is green and orange; the kids are either green or orange. I plan on keeping them and tracking their growth rate. Perhaps someone that reads this is looking for a science project and is willing to measure them from a time series of digital images?
Favia coral releasing a planula. Photo from when Dr. James was a professor at the Bermuda Institute of Ocean Sciences.