Anemones are Cnidarians, a phylum that also includes jellyfish which emerged 200 million years before the Cambrian explosion that produced most of the phyla we now think of as animals, including ours (Chordata). They reproduce both asexually, by cloning and splitting themselves, and sexually, by spawning ova and sperm into the water, like what we see in this photograph. Spawning occurs after dark and is coordinated with the lunar cycle. All individuals spawns simultaneously to increase the chances that two gametes will meet, settle, and produce a polyp. I was lucky enough to jump in the water and see this happen before my eyes. You can see this anemone's resident clownfish hiding in the corner.