Lions are considered "reef safe" with caution. They don't pose any threat to your sessile inverts but any decorative shrimps, crabs, etc. are likely to become snacks.

After the movie "Finding Nemo" came out, there was a spike in interest in keeping the types of fish that appear in the movie. I'm just a beginner myself trying to come up with a complete answer to the common "My kids want a Nemo Tank" questions.