If they don't reproduce by splitting..how DO they
They reproduce sexually:
Here is a quote from the Wakkiki Aquarium on Anemone Sexual Reproduction
"Sexual reproduction involves the production of eggs and sperm by the anemones themselves, there is no separate medusa (jellyfish) stage that produces eggs and sperm as in the life cycle of hydroids and sea jellies. Depending upon the species, sea anemones may have separate sexes, either male or female (dioecious), or a single individual may contain both male and female reproductive organs (hermaphroditic). And, depending upon species, sperm and eggs may either be released into the seawater in broadcast spawning, or sperm released by the male may fertilize eggs held within the female anemone's body. The anemone larval stage, called the planula, is a solid ball of cells. Hair-like cilia on its surface propel it over the bottom or up into the water. When the planula finds a suitable surface, it adheres to the bottom and changes form to become a young polyp with mouth, tentacles, and gut."