There are sea slugs that are reef safe but I don't remember the name. They do release poison into the water. I have a sea slug and I found out after the fact that it is toxic. It did get stuck in the filter but I saved it probably within minutes so it didn't squirt anything in the water. It has been probed by my camel shrimp a couple of times and nothing has happened - thank heavens. I have had the slug for nearly two months and I hope no disasters will happen in the future. They are a unique animal to watch along with the rest of the creatures in the aquarium.